Abstract:
A skywatcher&#39;s tripod has a seat mounted on a rider support that swivels 360 degrees on a base having upwardly foldable tripod legs. A post forms a forward end of the rider support. An extension arm configured to secure a tripod head for attachment of a surveillance device is axially slidable in a holder that is pivotally secured to the upper end of the post for rotation towards the seated user. The user sights on targets from horizon to zenith depending on the rotated position of the holder and the extension of the arm. The seat folds against the post outboard of the folded tripod legs and is held in folded position by a folded leg that abuts a handle that extends from a bottom side of the seat. The rider support includes a swivel lock and a combination holder/extension arm lock.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
   This disclosure is a Continuation-in-Part filed with an original application Ser. No. 11/483,363 filed Jul. 10, 2006, now abandoned. Benefit of earliest filing date is claimed for common subject matter. 

   STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
   Not applicable. 
   THE NAMES OF THE PARTIES TO A JOINT RESEARCH AGREEMENT 
   Not applicable. 
   INCORPORATION-BY-REFERENCE OF MATERIAL SUBMITTED ON A COMPACT DISC 
   Not applicable. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   This invention pertains to skywatching apparatus used to provide a steady support for a surveillance device such as a binocular, telescope, camera or camcorder. 
   2. Background Art 
   The conventional tripod commonly used for support of a telescope, binocular, camera, etc., is fine for training on a relatively stationary target such as a star but is severely limited for dynamic use acquiring and tracking a moving target such as a bird, airplane or unidentifiable object which may circle the observer&#39;s position and even pass overhead. Accordingly, it may be said that there are two different types of skywatching: static and dynamic. Dynamic skywatching requires the capacity to swivel 360 degrees while being able to quickly vary the elevation of the scope, camera or other surveillance device so as to aim it anywhere from ground level to directly overhead. The conventional tripod does not serve this market. Conventionally one stands behind the tripod with limited ability to pan the horizon, which can be boring and a discouragement to the casual skywatcher, and usually requires bending over to sight through a substantially straight line-of-sight surveillance device such as a binocular, which puts a strain on one&#39;s back. The conventional tripod does not incorporate a seat. Currently the best the industry has to offer for user comfort is a folding chair which, obviously, the skywatcher has to carry to the viewing site along with the tripod. For viewing subjects at higher elevations, conventional tripods incorporate a vertically movable column that can be cranked up and which has its upper end carrying the tripod head on which the surveillance device is mounted. This may make the tripod top-heavy, and if the user is standing, the column may not be raisable high enough for accessing the surveillance device&#39;s eyepiece without crouching, and close placement of a chair for sitting under the surveillance device is limited by interference with the tripod&#39;s legs and further restricts panning. For viewing targets at the zenith the industry offers a boom, a counterweighted end of which is secured to the tripod and the opposite free end of which carries the scope or binocular, the user standing or sitting under the free end of the boom. Besides being inconvenient with respect to the number of separate pieces of equipment which must be carried to the viewing site, this recourse still does not permit the user to swing about the horizon looking for a subject of interest; in order to do that he will have to step around the tripod (with risk of tripping on its legs) while repositioning the boom and the chair. Compensating for these limitations telescopes and spotting scopes are available having their eyepiece fixed at or adjustable to a 45 or 90 degree angle relative to the line-of-sight of the device so that the user need not tilt his head so for backward in order to look overhead, but such offset viewing is counter-intuitive, especially for the occasional user, and therefore a handicap when one is trying to quickly acquire a moving target. Binoculars still require sighting straight through the binocular. 
   The prior art has long sought to provide skywatchers with a support means including a swivel seat for searching 360 degrees about the user&#39;s location from horizon to zenith. The approach has been to provide the surveillance device mounted on an arm structure that rises from a position behind the seated user&#39;s back, swiveling with the seat, and overhanging and/or encircling the user, a free end of the arm structure holding the surveillance device in front of the user. This approach has proven impractical due to problems having to do with confinement of the seated skywatcher, obstruction of peripheral vision and proper alignment of the surveillance device&#39;s eyepiece with the user&#39;s eyes at different elevations of the surveillance device, as well as excessive weight due to complexity adversely affecting hand-carried portability or requiring assembly of parts at the skywatching site. The following prior art testifies to this history. 
   U.S. Pat. No. 4,637,536 entitled “Personal Binocular Support”, issued to Wilbur Wong, Jan. 20, 1987, discloses a binocular support that is worn by the user attached to the user&#39;s torso and so does not anticipate the structure of the present invention, but is of interest for its description of the prior art by referencing articles which appeared in issues of Sky and Telescope magazine ranging from January 1974 to February 1985. Pertinent paragraphs are quoted below: 
   “The problem of holding binoculars still enough for effective usage has long been recognized by astronomers. The most common method of overcoming this problem is to mount the binoculars to a common photographic tripod. While this approach solves the problem of unsteadiness, the tripod itself usually interferes with the position that the body of the user must assume when viewing objects at an angle of altitude from the horizon. Furthermore, few tripods are sufficiently tall enough to position the binoculars high enough for a tall user, when the user is looking up from a standing position. 
   “Accordingly the literature reveals various efforts to construct tripod attachments that mitigate the drawbacks of standard tripods. One such design, due to Steve Kufeld of Huntington Beach, Calif., is noted in the August 1979 issue of Sky and Telescope magazine, at pages 10 and 112. 
   “Kufeld&#39;s device, a counterbalanced mounting atop a heavy-duty tripod, is illustrated in use by a photograph of a person sitting on a stool and looking through a pair of binoculars fixed to the mounting. Through [sic] this apparatus is apparently of considerable utility, the photograph itself shows a principal disadvantage of such devices, as the user leans forward awkwardly from the stool to bring his eyes to the appropriate distance from the fixed tripod. Presumably the stool could be moved to a better position for at least some viewing angles; however, the picture also suggests another drawback—namely, that movement of the stool (or of the user&#39;s position if standing) is required to change the vertical viewing angle. 
   “Another tripod design aimed at overcoming this latter drawback is described by Rudolf Mandler of Deubach, West Germany, in the July 1982 issue of Sky and Telescope at pages 89 and 90. Mandler&#39;s tripod mount has an ‘inverted yoke’ that carries the binoculars in such a way that ‘the binoculars swing in a vertical plane around a pivot at [the] [sic] neck.’ By virtue of this action, it is ‘possible to view objects all the way to the zenith without twisting [the] [sic] body.’ This swinging action is a very important feature of Mandler&#39;s tripod and will be discussed further below. 
   “A less common but frequently publicized approach has been to build special chairs or chair attachments that support the binoculars through mechanical arms and brackets. Such arrangements provide more comfortable viewing positions for the user&#39;s body, particularly at higher viewing angles. 
   “Chris Baetens, of Boechout, Belgium, offers one of the simplest of such devices, shown in the February 1985 issue of Sky and Telescope at page 171. His device is made from an old revolving desk chair fitted with an adjustable framework to support the user&#39;s back, as the user assumes a near-reclining position to view the stars. Casters under the entire assemblage permit the user to swivel the chair, and adjustable arms support the binoculars above the back portion. 
   “Once the binocular support arms and the back framework are properly adjusted for the particular user&#39;s comfort and for the desired altitude angle, such a device supports the binoculars steadily, relieving the user&#39;s hands of this task. It of course offers considerable viewing satisfaction for the amount of design and construction effort invested. To change viewing angles, however, the user apparently must get up, adjust the back framework and probably the support arms as well, and then get back into the apparatus under the support arms. 
   “John Talbot, of Camarillo, Calif., writing in the same publication at page 172, has described a system that avoids this necessity. His chair rocks for altitude variation and rotates in azimuth, permitting a good view of the sky from about twenty-five degrees of altitude to the zenith—with one stop for chair adjustment along the way. 
   “Pearson Menoher, of Greenwich, Conn., in the January 1974 issue of Sky and Telescope at pages 51 through 55, discloses a more elaborate apparatus that eliminates the need for getting up and sitting back down to make adjustments. His apparatus is a motorized observing chair which tilts about a vertical axis for altitude-angle variation, and which rides a wheel-and-truck suspension for azimuth variation. The azimuth system is driven by a third-horsepower electric motor. This system may represent the ultimate in investment for binocular-viewing comfort, though perhaps not the ultimate in design elegance. 
   “Emphasizing the latter, or at least aiming to make the most of a much more modest investment in time and materials, are observing-chair designs introduced by John Riggs, of Kenmore, N.Y., and by Burt Leifer of Fort Wayne, Ind. These appear in Sky and Telescope for, respectively, February 1981 (pages 162 through 164) and May 1979 (pages 487 and 488). 
   “Each of these two approaches provides a chair with a simple azimuthal pivot about a vertical axis, and more importantly (as will be seen) a vertical swinging action of the binoculars themselves about a horizontal axis that is generally adjacent to the user&#39;s neck. 
   “Most of the tripods and chair brackets discussed above are difficult to adjust when changing viewing angles. These devices frequently require several separate adjustments to obtain the right position in both height and angle. The Mandler tripod and the Riggs and Leifer chairs minimize these problems by the swinging action of the binoculars about axes adjacent to the viewer&#39;s neck. 
   “ . . . [paragraphs omitted]. 
   “The multiple-adjustment problems mentioned above, as recognized by Mandler, Riggs, Leifer and others, arises from these translational and rotational movements. These natural movements of a person&#39;s head cause the eye position to traverse an arc when the head moves between a horizontal and an elevated viewing position. For present purposes this arc may be regarded as very roughly circular, with an apparent or effective center of motion that is near the person&#39;s neck. 
   “Thus both Mandler&#39;s tripod-attachment “yoke” and the binocular-supporting “fork” of Riggs&#39; and Leifer&#39;s chairs pivot about axes adjacent the user&#39;s neck. The location of the pivot axis relative to the user&#39;s body is discussed explicitly by both Riggs and Leifer. In each case the binocular eyepiece, being fixed to the yoke or fork, revolves about the same respective axis. As shown in Mandler&#39;s illustrations, however, the line of sight itself—that is, the centerline of the ocular—preferably does not pass through that mechanical-rotation axis. 
   “ . . . [paragraphs omitted]. 
   “Although of course the device is used generally in darkness, nonetheless there will remain for many users a continuing sensation of being enclosed or even confined. The crossbar and the swinging-structure side elements together form a moving cage, always occupying both sides of the user&#39;s peripheral vision. In other words, these tend toward the claustrophobic. This tendency is badly aggravated by the requirement that while viewing the user keep his body in practically the same position relative to the tripod or chair. 
   “Fifth and finally, all of the tripod and chair-bracket systems—even those of Mandler, Riggs and Leifer—are limiting in that their size and in some cases their weight inhibit the user&#39;s freedom of movement.” 
   End of quotations from the Wong patent. These back issues of Sky and Telescope magazine are no longer available for purchase and so the articles referred to in the Wong patent have not been directly examined and any photograph or illustration provided therein has not been seen by the instant inventor. However, recently introduced is a skywatching chair along the lines of those described above described as follows in a New York Times article dated Aug. 25, 2005: 
   “The StarSeeker chair from Bigha (bigha.com), an admittedly geeky contraption, aims to make stargazing comfortable. The $1,950 package consists of a rugged aluminum base, collapsible lounge chair, adjustable binocular mount and small battery-powered motor. It fits easily into a car trunk and assembles in a couple of minutes. 
   “The chair reclines smoothly under body pressure, and the viewing controls are easily operated in the dark. The counterweighted binocular bar allows a range of vertical motion, from just above the horizon to directly overhead. The motor, controlled by a small joystick, gently rotates the chair at variable speeds.” 
   The material quoted above shows that the prior approach has been to provide the surveillance device mounted on an arm structure that rises from behind the seated user, usually attached to a backrest, and to have such arm structure extending over or around the user, resulting in the undesirable sense of confinement discussed above. The present improvement solves all the problems previously experienced by effectively reversing the prior arrangement: the invention mounts the surveillance device on an arm structure that rises from a position IN FRONT OF the seated user, thereby leaving the areas to either side of and behind the user open, thereby providing the user with an unobstructed view of the area surrounding his position whereby a target approaching from a direction other than where the observer is currently looking can be spotted, and making it easy to get on and off the tripod because there no longer is any obstructing structure overhanging the seat. Further advantages are structural simplicity minimizing weight and enabling foldability to compact proportions for carrying by hand and not requiring assembly but simply unfolding for immediate use. 
   Referenced below is other prior art not pertaining to skywatching apparatus but showing elements relating to the present mode of attainment. 
   Bancalari, “Collapsable Pole And Stand Combination”, U.S. Pat. No. 4,744,536, issued May 17, 1988, discloses a pole having leg members pivotally secured between pairs of lug members forming part of a base, the lug members being provided with notches and the leg members with pins received in the notches whereby a leg detent means is effected for securing the leg members in alternative folded and unfolded positions, the leg members being foldable upwardly parallel to the pole and including spring means biasing the leg members into engagement with the notches. A similar means is used in the present invention. The preamble of Claim  1  appended hereto recites this structure as prior art forming a setting for the portion improved upon. 
   Sligh, “Drummer Seating System”, Patent Application Publication No. US 2004/0100132 A1 published May 27, 2004, anticipates the broad idea of a swivel seat wherein a payload (in this instance a drum) is mounted on an arm structure that is located in front of and swivels with the seat so that the seat is thereby effectively a saddle seat. The broadest claim presented herein is restricted to structure that differs from that disclosed by Sligh as necessary to give physical expression to a concept that is different from that envisioned by Sligh. The result conceived by Sligh is the support of one or more drums (which may be fairly large in diameter as shown in Sligh&#39;s drawings) and the drums must be carried at a low enough elevation that the drum can be played. Sligh provides a seat fixed to a “mounting block 22” that swivels on the upper end of a column that is held upright on three or four foldable legs. Sligh provides an “angled supporting arm 3” that is fixed at one end to the mounting block and extends forwardly therefrom a considerable distance as necessary to accommodate a drum of large diameter. The supporting arm has an offset configuration such that a straight free end portion of the arm is at a much lower elevation than is the end that is attached to the mounting block. “A vertical drum support post 1 is adjustably attached along the distal end of the angled supporting arm 3 via a screw clamp junction 25.” (Sligh [0026].) The support post 1 stands alongside the supporting arm 3 (as opposed to standing on top of it), and, is slidable axially of the distal end of the supporting arm 3 by loosening and then tightening the screw clamp junction 25. This axial adjustability of the standing position of the support post 1 evidently is necessary in order to position a drum closer to or further away from the seated musician depending on the diameter of the drum. Finally, the drum is mounted on a second clamp that is provided at the upper end of the support post and this second clamp is pivotally adjustable so that the tilt angle of the drum can be adjusted. Accordingly, the result conceived by Sligh is characterized in part by the idea of enabling a seated drummer to swivel left or right with the drum remaining in front of him at a suitably low elevation. As shown in Sligh&#39;s drawings, the attainment of this result requires the upper end of the “drum support post 1” to terminate at the elevation of the seat pad 12, FIG. 2. The offset or angled configuration of the supporting arm 3 is necessary to attain that result. The second clamp at the top of the drum support post that secures the drum is made pivotal for the sole purpose of giving physical expression to an idea that the tilt angle of the drum should be adjustable. This contrasts with the invention tripod wherein a pivotal connection at the upper end of the post member in cooperation with an extension arm functions to enable all those elevations of the surveillance device which are above the horizon. The present invention differs from Sligh as discussed below. 
   The result conceived by the present invention is that of supporting a surveillance device as steadily as possible at elevations ranging from the eye level of the seated user for sighting on targets located on the horizon, and at increased elevations all the way to the zenith. This result conceived is further characterized by the idea of the structure which gives physical expression to that result conceived being compactly foldable comparable to a conventional heavy duty photographer&#39;s or surveyor&#39;s tripod. That structure as most broadly claimed herein, requires (a) an L-shaped rider support comprising an elongate main member of given length and an elongate post member having a length that is longer than that of said main member secured to the forward end of the main member, the main member being pivotally secured to a base for rotation 360 degrees about a swivel axis, the base having upwardly foldable tripod legs; (b) the rider support having a plane of symmetry that extends lengthwise of the main member and includes the post member and the swivel axis; (c) having a seat fixed to an elongate seat support member that is positioned on a top side of and extends lengthwise of the main member centered on the said plane of symmetry, the seat support member having a forward end pivotally secured to the main member for rotation about a seat pivot axis that is perpendicular to the said plane of symmetry and is located such that the seat is foldable against a rearward side of the post member for compact foldability; (d) wherein a holder carrying an extension arm (that is relatively short for compact foldability) is pivotally secured to an upper end of the post member, the post member being longer than the main member in order to (1) position a surveillance device mounted on the extension arm at the eye level of a seated user for sighting on targets located on the horizon and (2) enable the extension arm to pivot (via the holder) from an elevation that is high enough that the extension arm when extended can position the surveillance device overhanging the seated user&#39;s head for sighting on targets at the zenith; (e) the extension arm and its holder being centered on the plane of symmetry in order that the surveillance device will be positioned on a logically centered line-of-sight; (f) wherein the tripod legs are long enough that when the seat and legs are in their respective unfolded positions, the seat is located wholly inboard of an imaginary straight line drawn between the free ends of any two of the leg members in order that the tripod will be safely usable on a gradient without the user falling over backwards; and (g) wherein (for most compact foldability) the main member has a length so short as measured from the swivel axis to the post member that foldability of the tripod legs requires (1) folding the seat against the post member as stated above and also (2) centering the rider support between two of the legs in order that a bottom surface of the seat will clear the planes of foldability of the said two legs so that when the said two legs are standing upright in their folded position the folded seat is located immediately outboard of the said two leg members. 
   Kuo, “Foldable Stand Assembly For Microphones”, U.S. Pat. No. 6,007,032, issued Dec. 28, 1999, discloses a lower pole section standing on upwardly foldable and securable legs but having an upper pole section that is axially slidable within a holder that is pivotally secured to the lower section of the pole, the upper end of the extendible pole being configured to hold a microphone which can be leaned toward the user by pivoting the holder relative to the lower section of the pole, but this can only be done after the upper pole section is lifted entirely free of the lower section of the pole because in fully retracted position the upper pole section is received inside the lower section of the pole. The Kuo patent also illustrates art prior to the patent pertaining to a stand comprising a first pole that rises from tripod legs, having a telescopically contained second pole mounted in the first pole, an upper end of the second pole having a holder clamped onto it which in turn carries a third pole that is axially slidable within the holder, the third pole being held parallel to but laterally spaced apart from the main pole structure, the third pole being rotatable and extendible in the holder, a thumbscrew turned on the pivotal axis of the holder pushing an axially movable first plate of the holder against a second plate that is clamped onto the upper end of the second pole; whereby, the upper end of the third pole which is configured for attachment of a microphone can be positioned and locked at various elevations and extensions, both of which are simultaneously locked by rotation of the thumbscrew, the construction providing a folded position of the third pole wherein it is fully retracted and stands parallel to the first and second pole sections, but laterally spaced apart so that it is not in the plane of symmetry of the first and second pole sections. Since the thumbscrew turns on the pivotal axis of the holder, this construction is satisfactory only for carrying a lightweight device such as a microphone and not the much heavier surveillance devices which the instant holder must hold steady. 
   Krien et al., “Portable Seat and Platform Support”, U.S. Pat. No. 6,895,709 B1, issued May 24, 2005, discloses several embodiments of a table-like “platform” that is detachably clamped to the upper end of a post by means of a cap screw that is threaded through a coupling that is provided on an underside surface of the platform. Tripod legs are detachably clamped to a lower end of the post. The post is cylindrical and has a cylindrical collar on it that is slidable up or down on the post and is also rotatable around the post, the post defining a swivel axis. An arm member has an inboard end fixed to the collar so that the arm member projects laterally from the collar. A backless seat is fixed to the outboard end of the arm member. The post is provided with holes which are engaged by a pin that in one embodiment passes through a locking ring that is positioned under the collar whereby the elevation of the collar on the post is set but the seat can still be rotated around the post; and in another embodiment the pin passes through the collar itself whereby the seat cannot be rotated around the post. Since Krien&#39;s seat is supported at the end of an arm that projects radially from the post, it constitutes a saddle seat, but it does not swivel in the sense of carrying the post around a swivel axis; it does the reverse: it orbits around the stationary post which defines the swivel axis; the post cannot be swung 360 degrees around Krien&#39;s seat. The Krien saddle seat is not foldable. 
   Vodinh, “Folding Seat Assembly”, U.S. Pat. No. 6,224,153 B1, issued May 1, 2001, discloses a backless and foldable saddle seat that is attached to a seat bracket that slides axially of one end of a first arm member that has its opposite end pivotally attached to a first clamp. A second arm member under the first has one end pivotally secured to the seat bracket and has its opposite end pivotally secured to a second clamp. The clamps enable attachment of the seat to one of the two posts that hold up the ends of a tennis net; the result conceived being to provide a seat on which a player can rest when not playing, the seat being raisable to a folded storage position when the game is in progress. In the unfolded position of the seat the first and second arm members form a triangular support for sturdy support of the seat, the seat being foldable upwardly parallel to the post due to the pivotal connections at the ends of the arm members in cooperation with the axial slidability of the seat bracket. Obviously, the net post that is shown in Vodinh&#39;s drawings is not a part of the unitary structure that Vodinh discloses; the net post is shown in the drawings merely to illustrate the manner of using the seat assembly. In the present disclosure, the post member is a part of the combination that is claimed, the seat being foldable against the post member. Other differences are that the invention&#39;s backless seat is fixed stationary (not axially slidable) on a single support member (not two arms which are hinged together), and the support member is pivotally secured to the main member (not the post member); collectively a much simpler construction that puts the seated person&#39;s weight on the main member and not on the post member which has to provide steady support for a surveillance device. 
   Finally, the prior art includes “tripod heads”—an adaptor that is conventionally fitted to the top of a tripod and provides the means by which a surveillance device such as telescope, spotting scope, binocular, camera, camcorder, etc., is made attachable to the tripod. There are numerous specifically different forms of such adaptors. A herein preferred type is the so-called “ball head”, typically having a cylindrical main body portion containing a rigid ball a portion of which is configured to enable a screwed-on attachment of the surveillance device, the cylindrical body portion containing as a clamp that obtains a grip on the ball by manual manipulation of a side-mounted lever whereby the surveillance device can be aimed universally within the range of movability of the ball inside the cylindrical body.  FIG. 3  in the accompanying drawings, labeled as prior art, illustrates such a ball head type of tripod head. It is not a claimed element of the invention. 
   BRIEF SUMMARY OF THE INVENTION 
   The new and useful result conceived is a skywatcher&#39;s tripod comparable to a conventional heavy duty photographer&#39;s or surveyor&#39;s tripod in weight, compact foldability and hand-carried portability, but inclusive of a swivel seat that enables a seated user to quickly aim a surveillance device 360 degrees compass bearing from ground level to directly overhead in order to quickly acquire and track a moving target; wherein 
   (a) the surveillance device is mounted on the upper end of a single straight elongate extension arm that is axially slidable within a holder that is pivotally secured to the upper end of a post member that forms the forward end of an L-shaped rider support on which the seat is mounted, so that the structure supporting the surveillance device is located wholly IN FRONT OF the seat, thereby affording quick access on and off the tripod as well as unobstructed peripheral vision around the tripod and thereby solving every problem discussed in the Wong patent; wherein: 
   (b) the rider support, seat and extension arm elements have a common plane of symmetry so that the seated user is provided a logically centered line-of-sight through the surveillance device; and wherein: 
   (c) compact foldability and hand-carryable portability are provided by a combination of features comprising (1) providing the seat foldable against the post member, (2) providing the post member located so close to the seated user&#39;s chest and thereby the swivel axis that foldability of two of the leg members requires centering of the rider support between the said two leg members with the seat in its folded position so that a bottom surface of the seat minimally clears the planes of foldability of the said two leg members, and (3) providing the seat support member inclusive of a handle that when the seat is unfolded depends from the seat support member for storage, but when the seat is folded, a third leg member when in upright folded position substantially abuts the handle and thereby holds the seat in its folded position while simultaneously holding the handle in its unfolded usable position. 
   The mode of attainment includes prior art structure comprising a base defining a swivel axis, having tripod legs pivotally secured to the base for rotation about axes orthogonal to the swivel axis, the tripod legs having an unfolded position supporting the base at an elevation above a ground surface and having a folded position rising upwardly from the base parallel to the swivel axis, further including spring-biased detent means securing the legs in their alternative folded and unfolded positions. The preamble of Claim  1  appended hereto distinguishes these elements as prior art forming the necessary setting for the portion improved upon. 
   The improvement provides an L-shaped rider support that comprises an elongate main member that is pivotally secured to the said base for rotation 360 degrees about the swivel axis, and an elongate post member that is secured to a forward end of the main member such that the post member stands preferably perpendicular to the main member, the rider support having a plane of symmetry that extends lengthwise of the main member and includes the post member as well as the swivel axis. An elongate seat support member located on a top side of and extending lengthwise of the main member is likewise centered on the plane of symmetry, the seat support member having a forward end pivotally secured to the main member near the post member for rotation about a seat pivot axis that is perpendicular to the plane of symmetry. A backless seat is secured to a top side of the seat support member centered on the plane of symmetry. The seat support member and the seat mounted on it have a common unfolded position parallel to the main member and are pivotal together about the seat pivot axis to a folded position wherein a top side of the seat stands against a rearward side of the post member. A skywatching tripod must be compact enough that it can conveniently be hand-carried, as it frequently happens that one can park his or her vehicle at one location but must then carry the tripod into a field where there is enough open sky for productive skywatching. The invention tripod achieves such compactness by providing the post member positioned as close as possible to the seated user&#39;s chest; i.e., as close to the swivel axis as clearance for using the surveillance device will permit. In the unfolded position of the seat, the seat support member has to be long enough that enough of it is resting on the main member for secure support of the seated user without excessive strain either on the seat support member or on its pivotal connection to the main member, as well as being long enough for support of the seat itself; but at the same time, the seat has to be located far enough forwardly (i.e., close enough to the swivel axis) that the seat in unfolded position is located wholly inboard of an imaginary straight line drawn between the free ends of any two leg members so that the center of gravity of the person sitting on the seat is located close enough to the swivel axis that the possibility of tipping over backwards when the tripod is standing on a gradient is minimized. This result is attained by a combination of features comprising the leg members being made especially long so as to reach further outwardly than is typical of conventional tripods, in combination with the seat pivot axis being located as close as possible to the post member, such that, when the seat is folded, a top surface of the seat is positioned against a rearward side of the post member. 
   For maximum compactness, the main member has a length as measured from the swivel axis to the post member that is so short that two of the leg members cannot be folded unless (A) the seat is in its folded position with its top surface against the rearward side of the post member, (B) the rider support is centered between the said two leg members so that a rearward end of the main member is thereby aligned with the third one of the leg members, and (C) a bottom surface of the seat only minimally clears the planes of foldability of the said two leg members. Accordingly, a distinguishing characteristic of the present tripod is that two of its leg members are foldable only when the seat is in its folded position and the rider support is centered as described. Unobstructed foldability of the said third leg member is provided by the rearward end of the main member terminating short enough of where the said third leg member is pivotally connected to the base that the said third leg member can be folded upright parallel to the swivel axis. 
   The mode of attainment includes an extension arm slidably mounted in a holder, the extension arm and holder having a common longitudinal axis. The holder is pivotally secured to the upper end of the post member for rotation about a holder pivot axis that perpendicularly intersects the said plane of symmetry and is located forwardly of a forward side of the post member such that the holder can be pivoted to a position that holds the extension arm parallel and as close as possible to the forward side of the post member, the holder being positioned axially of the holder pivot axis such that the said longitudinal axis lies wholly within the rider support&#39;s plane of symmetry. 
   The extension arm has a fully retracted position in the holder such than an upper end of the extension arm is substantially flush with an upper end of the holder, and the extension arm has a minimal length such that when the extension arm is in its fully retracted and pivotally folded position parallel to the forward side of the post member, a lower end of the extension arm terminates short of the leg members in their unfolded position so that the rider support can always be swiveled 360 degrees without the extension arm abutting any of the leg members even when the extension arm is fully retracted and pivotally folded. The proportions are such that a surveillance device mounted on the extension arm can be sighted on the horizon when the extension arm is in its fully retracted and pivotally folded position. 
   The upper end of the extension arm is configured for attachment of a tripod head (not a claimed element). Rotation of the holder approximately 45 degrees towards a seated user, combined with full extension of the extension arm having the length specified in paragraphs above and below will locate a tripod head carried by the extension arm at an elevated position overhanging the seated person&#39;s head, such that, a surveillance device mounted on the tripod head will be adjustable to a line-of-sight straight through the surveillance device at a target that is located at the zenith. 
   The height of the post member (i.e., its length) plays a part in determining the length of the extension arm. The extension arm must be short enough not to abut the leg members in their unfolded position as stated in a paragraph above, but must still be long enough that its upper end can locate a surveillance device over the seated person&#39;s head under the conditions specified in a paragraph above. Both requirements are met by providing the post member having a length such that, when the extension arm is in its fully retracted and pivotally folded position standing parallel to the forward side of the post member, a surveillance device mounted on a tripod head that is affixed to the upper end of the extension arm is located substantially at the eye level of the seated user; in other words, at an elevation such that said person can sight horizontally straight through the surveillance device at a target that is located on the horizon. It has been found that a post member having such a length enables use of an extension arm that is long enough to enable sighting at the zenith and yet is short enough to be compactly foldable. 
   The seat support member has a rearward end portion that extends outboard of the base when the seat support member is in its unfolded position parallel to the main member. A handle is fixed to an underside of this rearward end portion of the seat support member, the handle being attached such that when the seat support member is in its unfolded position the handle is in a storage position depending from the seat support member, the rearward end portion of the seat support member extending far enough outboard of the base that the handle hangs spaced above the leg members when the leg members are in their unfolded position so that there is no interference therebetween. The handle has a length such that (a) when the seat is in its folded position standing against the post member, and (b) the rider support is centered between two leg members so that the rearward end of the main member is thereby aligned with the third one of the leg members, and (c) the third leg member is in its folded position standing upright parallel to the swivel axis, a free end of the handle is substantially in abutment with the said third leg member, with the result that the third leg member prevents unfolding of the seat from its upright storage position while at the same time holding the handle in its usable position for carrying the tripod. 
   Finally, other objects of the present improvement are (a) to provide the elevation of the extended extension arm lockable by a means that takes into account the significant weight of the surveillance device that may be carried, and (b) to provide a swivel lock means that can be applied virtually instantaneously so that the surveillance device can immediately be stopped on a target that suddenly makes its appearance, and which can be applied while the user continues to sight through the surveillance device. 

   
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       FIG. 1  is a side elevational general view of the invention skywatcher&#39;s tripod in a first in-use position with the tripod leg members and the seat in their respective unfolded positions, the extension arm fully retracted and the extension arm holder in its pivotally folded position holding the extension arm parallel to the forward side of the post member, and with a handle for carrying the tripod in a storage position depending from the seat support member. The user has provided a ball head type of tripod head and it is shown in side view attached to the upper end of the extension arm, and the user has also provided a surveillance device, in this instance a spotting scope, represented schematically, attached to the ball head.  FIG. 1  shows the ball head holding the scope in a horizontal position aimed at the horizon. Phantom lines indicate that the holder can be rotated rearwardly 45 degrees. A centerline identifies the swivel axis about which the rider support is rotatable. 
       FIG. 2  is drawn to the same scale as  FIG. 1  and is a similar side elevational general view but showing the tripod in its fully folded configuration with the scope having been removed from the ball head and the ball element rotated downward for its protection and to minimize overall height.  FIG. 2  shows the seat folded against the post member and the leg members folded upwardly from the base parallel to the swivel axis.  FIG. 2  shows the handle abutting one of the leg members whereby the seat is held in its folded position and the handle is held in its usable position. 
       FIG. 3  is an enlarged front two-quarter perspective general view of the prior art ball head type of tripod head that is shown attached to the extension arm in  FIGS. 1 ,  2 ,  5 ,  6 ,  7  and  8 . 
       FIG. 4  drawn to the same scale as  FIG. 3  and is an enlarged broken away side two-quarter perspective view showing how the upper end of the extension arm is preferably configured for attachment of the ball head to the extension arm, with setscrews used for securing the ball head shown in exploded relationship relative to the screw-threaded holes in which the setscrews are received. 
       FIG. 5  is drawn to the same scale as  FIG. 1  and is a similar side elevational general view showing the tripod in a second in-use position wherein the holder has been pivoted rearwardly a few degrees and the extension arm has been partially extended to elevate the scope for aiming it skyward. 
       FIG. 6  is drawn to the same scale as  FIG. 5  and is a similar side elevational general view showing the tripod in a third in-use position wherein the holder has been pivoted rearwardly a full 45 degrees and the extension arm has been fully extended in order to aim the scope at a target that is located directly overhead. 
       FIG. 7  is a top elevational general view of the tripod drawn to the same scale as  FIG. 1  and taken on the line  7 - 7  of  FIG. 1 , showing the extension arm and its holder in the same position as it is shown in  FIG. 1  but without the scope attached to the ball head and with the ball element of the ball head rotated into the horizontal position in which it is shown in  FIG. 2 .  FIG. 7  provides a top view of the seat in its unfolded position.  FIG. 7  also provides a top view of the base with the tripod leg members in their unfolded position, a rearwardly positioned leg member being shown in full length and the other two forwardly positioned leg members having their outer portions broken away in order to fit the view on the sheet.  FIG. 7  shows the rider support centered between the two forwardly positioned leg members so that it is aligned with the third one (rearwardly positioned) of the leg members. 
       FIG. 8  is a is top elevational general view of the tripod similar to and drawn to the same scale as  FIG. 7  and taken on the line  8 - 8  of  FIG. 2 ,  FIG. 7  providing a top view of the seat folded against the post member. In  FIG. 8  the three leg members are seen endwise because folded. As in  FIG. 7 ,  FIG. 8  shows the rider support centered between the two forwardly positioned leg members.  FIG. 8  shows that when rider support is centered as stated and the seat in its folded position standing against the post member, a bottom surface of the seat only minimally clears the planes of movability of the leg members. Dashed lines indicate the previously unfolded position of the leg members in which they are shown in  FIG. 7 . In  FIG. 8  heavy lines superimposed on the forwardly positioned leg members identify their planes of movability. 
       FIG. 9  is a greatly enlarged detail view in three-quarter perspective of the rider support mounted on a broken away top portion of the base, the rider support including the holder with the extension arm mounted in the holder, the upper end of the extension arm being sectioned away, showing a section only of the seat support member pivotally secured to the rider support.  FIG. 9  provides a close view of the extension arm holder, showing it to be pivotally locked by a thumbscrew which is shown in exploded relationship relative to the lug member in which the thumbscrew is received.  FIG. 9  shows the rider support as seen from its right-hand side and from its rearward end ( FIGS. 1 ,  2 ,  5  and  6  showing it from its left side). This right-hand view reveals a swivel lock means comprising an elongate steel rod that is manipulated by the seated user to jam the rod against a planar top surface of the base. 
       FIG. 10  is a top elevational general view of the tripod similar to and drawn to the same scale as  FIG. 7  but showing all three of the leg members in full length and showing the rider support swiveled 60 degrees (relative to the position in which it is shown in  FIG. 7 ) so that in  FIG. 10  the seat is positioned centered between two of the leg members.  FIG. 10  shows the seat located wholly inboard of an imaginary straight line (represented by a phantom line) that has been drawn between the free ends of the said two leg members. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Referring to the accompanying drawings, a skywatcher&#39;s tripod according to the present improvement includes prior art comprising a base, indicated generally as  10 ,  FIGS. 1 and 10 , defining a swivel axis  11 , three leg members  12 ,  13 ,  14 ,  FIG. 10 , pivotally secured to the base  10  for rotation about leg pivot axes  12 ′,  13 ′,  14 ′, respectively,  FIGS. 8 and 10 , which are orthogonal to the swivel axis  11 , the base  10  including three pairs of parallel spaced apart base lugs as at  15 ,  16 , in  FIGS. 1 and 2 , between which the leg members, such as leg member  13  in  FIG. 1 , are secured. Each leg member includes a pin as at  17 ,  FIG. 1 , that is received in notches as at  18  (associated with leg member  13 ) and  19  (associated with leg member  14 ), which are formed in each pair of base lugs, whereby the leg members are securable in an unfolded position as shown in  FIG. 1  wherein the leg members are positioned inclined downwardly from the base  10  in order to support the base  10  at an elevation spaced above a ground surface  20  on which the tripod stands, and alternatively, are securable in a folded position as shown in  FIG. 2  wherein the leg members are seen standing upright encircling the base  10  parallel to the swivel axis  11 . Each leg member has a spring as at  21 ,  FIGS. 1 and 2 , that is connected at one end as at  22  to the leg member and is connected at its opposite end as at  23  to the base  10  whereby the leg member is biased to engage one or the other of the detent notches. 
   The claimed improvement pertains in part to the provision of a rider support, indicated generally as  24 ,  FIGS. 1 and 9 , comprising an elongate main member  25 ,  FIGS. 1 and 9 , that is pivotally secured to the base  10 ,  FIG. 1 , for rotation 360 degrees about the swivel axis  11 ; further comprising a post member, indicated generally as  26 ,  FIGS. 1 and 9 , that is secured to a forward end  27  of the rider support  24  such that the post member  26  stands perpendicular to the main member  25 , the rider support  24  having a plane of symmetry, labeled as such in  FIG. 9  and drawn in phantom outline having a broken away top border, the plane of symmetry extending lengthwise of the main member  25  and including the post member  26  and the swivel axis  11 ; further comprising an elongate seat support member, indicated generally as  28 ,  FIGS. 1 and 9 , that is located on a top side  25 T,  FIG. 9 , of the main member  25 , the seat support member  28  extending lengthwise of the main member  25  and being likewise centered on the plane of symmetry ( FIG. 9 ), the seat support member  28  having a forward end  30 ,  FIG. 9 , that is pivotally secured to the main member  25  near the post member  26  for rotation about a seat pivot axis  31 ,  FIGS. 1 ,  9  and  10 , that is perpendicular to the said plane of symmetry; further comprising a backless seat, indicated generally as  32  in  FIGS. 1 ,  2 ,  5 ,  6 ,  7 ,  8  and  10 , secured to a top side  33 ,  FIGS. 1 ,  5 ,  6  and  9 , of the seat support member  28  and likewise centered on the said plane of symmetry, the seat support member  28  and the seat  32  mounted on it having a common unfolded horizontal position as shown in  FIG. 1  wherein they are parallel to the main member  25 , and being pivotal upwardly together about the seat pivot axis  31 ,  FIGS. 1 and 9 , to a folded position as shown in  FIGS. 2 and 8 , standing upright parallel to the swivel axis  11  ( FIGS. 1 and 2 ) with a top surface  34 ,  FIGS. 1 ,  2  and  8 , of the seat  32  against a rearward side  35 ,  FIGS. 1 and 9 , of the post member  26 , the seat  32  being positioned lengthwise of the seat support member  28  such that in the unfolded position of the seat  32 , the seat  32  is located wholly inboard of an imaginary straight line X,  FIG. 10 , drawn between the free ends (such as  36 ,  37 ,  FIG. 10 ) of any two of the leg members (such as  13 ,  14 ,  FIG. 10 , respectively) when in their unfolded position standing on a ground surface  20 ,  FIG. 1 , whereby the center of gravity Y of a person sitting on the seat  32  is close enough to the swivel axis  11 ,  FIG. 10 , that there is little likelihood of the seated person falling over backwards when the tripod is situated on a gradient. 
   Folded compactness comparable to a conventional heavy duty photographer&#39;s or surveyor&#39;s tripod is attained by providing the main member  25 ,  FIG. 2 , having a length as measured from the swivel axis  11  to the post member  26  such that (A) when the seat  32 ,  FIG. 2 , is in its folded position with its top side  34  against the rearward side  35 ,  FIG. 1 , of the post member  26  as shown in  FIGS. 2 and 8 , and (B) the rider support  24  is centered between any two of the leg members (such as  12 ,  13  in  FIGS. 7 and 8 ) so that a rearward end  38 ,  FIGS. 1 ,  2 ,  8  and  9 , of the rider support  24  is thereby aligned with the third one of the leg members (such as  14  in  FIGS. 2 and 8 ), a bottom surface  39 ,  FIG. 8 , of the seat  32  only minimally clears the planes of foldability  40 ,  41 ,  FIGS. 7 and 8 , of the said two leg members  12 ,  13 , respectively, so that, assuming the seat  32  has a comfortable width such as 30.48 cm (12 inches), the said two leg members ( 12 ,  13 ) are foldable only when the seat  32  is in its folded position with the rider support  24  centered as described. 
   The rider support  24  further includes an extension arm, indicated generally as  42 ,  FIGS. 1 ,  2 ,  5 ,  6  and  9 , slidably mounted in a holder, indicated generally as  43 , that is pivotally secured to the upper end, indicated generally as  44 ,  FIG. 9 , of the post member  26  for rotation about a holder pivot axis  45 ,  FIG. 9 , that perpendicularly intersects the rider support&#39;s plane of symmetry, the extension arm  42  and its holder  43  having a common longitudinal axis  46 ,  FIG. 9 , that is located in said plane of symmetry. The plane of symmetry,  FIG. 9 , is drawn in phantom line outline, and the broken line top border indicates that the plane of symmetry actually continues upwardly so as to encompass the holder  43 ,  FIG. 9 , as well as the extension arm  42  at every position of its extension and rotation. 
   A pair of lug members  47 ,  48 ,  FIG. 9 , form the upper end of the post member  26 , the lug members  47 ,  48 , having corresponding free end portions  49 ,  50 , respectively, that extend further forwardly of the forward side  51 ,  FIG. 5 , of the post member  26 ,  FIG. 9 , spaced apart parallel to and equidistant from opposite sides of the plane of symmetry, and the holder  43  is pivotally secured between the free end portions  49 ,  50 , of the lug members  47 ,  48 , respectively, such that the holder  43  can be rotated to a folded position as shown in  FIGS. 1 ,  2  and  9 , that holds the extension arm  42  parallel to the forward side  51 ,  FIG. 5 , of the post member  26  and as close as possible to it as shown in  FIGS. 1 ,  2  and  9 . 
   As shown in  FIGS. 1 and 2 , the extension arm  42  has a fully retracted position in the holder  43  such that an upper end  52 ,  FIG. 5 , of the extension arm  42  is substantially flush with an upper end  53  of the holder  43 , as shown in  FIG. 1 , and the extension arm  42  has a length such that, when the extension arm  42  is fully retracted and is positioned parallel to the forward side  51 ,  FIG. 5 , of the post member  26  and the leg members are in their unfolded position as shown in  FIG. 1 , the lower end  54 ,  FIG. 1 , of the extension arm  42  terminates short of the leg members so that the rider support  24  can be swiveled 360 degrees without the extension arm  42  abutting any of the leg members even when the extension arm  42  is in the fully retracted and pivotally folded position in which it is shown in  FIG. 1 . 
   For most rigid (stationary) support of a surveillance device, the extension arm  42  must be as short as possible in order to minimize unintended flexure that is inherent in the material from which the extension arm  42  is constructed, which, in this embodiment, is a cross-sectionally square aluminum tube (tubing being used for lightness of weight and aluminum being preferred for the same reason). The length of the extension arm  42  is minimized by proportioning the post member  26  such that, when the extension arm  42  is in its fully retracted and pivotally folded position as shown in  FIG. 1 , a straight line-of-sight surveillance device, such as a binocular or the scope  55  seen in  FIG. 1 , is held at the eye level of a person seated on the seat  32  so that such person can sight straight through the device at a target that is located on the horizon. 
   The upper end  52 ,  FIG. 5 , of the extension arm  42  is configured for attachment thereon of a tripod head. A ball head type of tripod head is preferred because it enables universal aiming of the surveillance device within the range of movability of the ball element that is incorporated in the ball head. A typical conventional configuration of such a ball head tripod head is shown in  FIG. 3 , indicated generally as  56  in  FIG. 3  and also in  FIGS. 1 ,  2 , and  5  through  8 . It comprises a typically cylindrical housing  57 ,  FIG. 3 , containing a ball  58  onto which the housing  57  effectively obtains a clamped grip by manipulation of a lever  59 . The ball  58  is formed inclusive of a short post  60  that has an upper end defining a face plate  61  that is provided with a screw end  62  that is fixed to the faceplate  61  and which, by rotation of the faceplate  61  (after first loosening the ball  58  by manipulation of the lever  59 ), can be turned into a correspondingly screw-threaded opening (not shown) that is conventionally provided in the underside of surveillance devices which are designed for attachment to a tripod. A slight turn of the lever  59  in one direction loosens the grip of the housing  57  on the ball  58  whereby the angular position of the surveillance device on the ball head  56  is adjustable; turning the lever  59  in the opposite direction locks the ball  58 . Conventionally the housing  57  is provided with a notch  63  (some ball heads provide two notches located on opposite sides of the housing  57 ) into which the short post  60  can be lowered in order to thereby maximize the angular adjustability of the surveillance device relative to the housing  57 .  FIG. 2  shows the short post  60  of the ball head  56  in a position lowered into the notch  63 ,  FIG. 3 , so that the faceplate  61  which is shown upright in  FIG. 1 , is, in  FIG. 2  shown lowered into a storage position that better protects the screw end  62 ,  FIGS. 2 and 3 , and at the same time minimizes the folded height of the tripod. 
   Referring to  FIG. 4  which shows a broken away upper end portion of the extension arm  42 , the upper end  52  of the extension arm  42  is configured for attachment of a tripod head, in this instance, the ball head  56  that is shown in  FIG. 3 . Conventionally, the housing  57  of the ball head  56  is provided having its underside (not shown) provided with a screw-threaded opening and the conventional tripod is provided having its upper end incorporating a screw-end identical to element  62  of  FIG. 3 , whereby the housing  57  of the ball head  56  obtains a screwed on attachment to the upper end of the conventional tripod. A problem has been found in that, in the course of aiming an attached heavy surveillance device (such as a spotting scope or binocular) in different directions, there is a tendency for the ball head&#39;s housing  57  to become unscrewed. In the present embodiment, this possibility is precluded by not using the conventional screwed-on method of attachment but instead having a lower end margin of the ball head&#39;s housing  57  received in a cup  64 ,  FIG. 4 , that is fixed (e.g., by welding) to the upper end  52  of the extension arm  42 , and providing the cup  64  with a plurality of screw-threaded holes, such as at  65 , into which setscrews, such as at  66 , are turned and jammed against the housing  57  of the ball head  56 . See also  FIG. 5  showing the cup  64  fixed to the upper end  52  of the extension arm  42 , with the ball head  56  partially received inside and rigidly fastened to the cup  64  by a setscrew  66 . 
   The seat support member  28 ,  FIG. 1 , has a rearward end portion  67  that extends outboard of the base  10  when the seat  32  is in the unfolded position in which it is shown in  FIG. 1 . A handle, indicated generally as  68 , is provided fixed to the rearward end portion  67  so as to depend from same when the seat  32  is in its unfolded position; the handle  68  being at such time in a storage position. The outboard projection of the rearward end portion  67  and the length of the handle  68  are such that (a) there is enough clearance between the free end  69  of the handle  68  and the leg members that the rider support can be swiveled 360 degrees about the swivel axis  11  without the handle  68  striking any of the leg members, and (b) such that, when the seat  32  is in its folded position as shown in  FIG. 2  with the rearward end  38  of the rider support  24  aligned with a folded one of the leg members (such as leg member  14  in  FIG. 2 ), the free end  69 ,  FIG. 2 , of the handle  68  is proximate the folded leg member as shown in  FIG. 2 , with the result that the substantially abutting leg member (such as  14  in  FIG. 2 ) prevents unfolding of the seat  32  while simultaneously keeping the handle  68  in the horizontally disposed ready-for-use position in which it is shown in  FIG. 2 . 
   Returning to  FIG. 9 , in this embodiment the holder  43  comprises two elongate planar parallel spaced apart side members  70 ,  71 , which are rigidly fastened together by screws or rivets a visible end of one of which is indicated at  72 , each of which screws or rivets passes through a spacer, one of which is indicated at  73 , the spacers being located along lengthwise margins of the side members  70 ,  71 , and being spaced apart from each other as necessary for close support of the four sides of the extension arm  42  with operating clearance therebetween to permit the extension arm  42  to be moved axially of the longitudinal axis  46  within the holder  43  (the uppermost corner of holder  43  is broken away to fit the view on the sheet). The side members  70 ,  71 , are identical, so what is next described in connection with side member  71  applies as well to side member  70 . 
   Side member  71 ,  FIG. 9 , is provided with a pair of parallel spaced apart slits S 2 , S 3 , which creates a segment  74  of side member  71  that is depressible against the adjacent side of the extension arm  42 . The end portion  50  of lug member  48  is provided with a screw-threaded hole  75  that is RADIALLY REMOVED FROM the pivotal axis  45  of the holder  43 ; i.e., the screw-threaded hole  75  has a hole-center axis  76  that is parallel to and is SPACED APART FROM the holder&#39;s pivotal axis  45 . The hole-center axis  76  intersects the depressible segment  74  of side member  71 ,  FIG. 9 , and likewise intersects a corresponding depressible segment  77  of side member  70 ,  FIG. 6 ; lug member  47 ,  FIG. 6 , being provided with a screw-threaded hole  78  that corresponds with screw-threaded hole  75  and is likewise formed concentric about hole-center axis  76 ,  FIG. 9 . 
   A thumbscrew, indicated generally as  79  and shown in exploded relationship in  FIG. 9 , has a screw-threaded end  80  that is turned into the hole  75  so as depress the segment  74  against the extension arm  42  and thereby simultaneously lock pivotal movability of the holder  43  and axial movability of the extension arm  42 .  FIG. 9  shows the holder  43  in its pivotally folded position wherein it is positioned parallel to the post member  26 . In this folded position of the holder  43 , the screw-threaded end  80  of the thumbscrew  79  strikes the depressible segment  74  of the holder  43  at a point thereon that is very close to slit S 2 . The holder  43  is rotatable 45 degrees in the direction indicated by arcuate arrow  81 . When the holder  43  is at its maximum 45 degree rotated position, the screw-threaded end  80  of the thumbscrew  79  strikes the depressible segment  74  of the holder  43  at a point thereon that is very close to slit S 3 . At all rotated positions of the holder  43  between fully folded position as shown in  FIG. 9  to fully rotated 45 degrees position as shown in  FIG. 6 , the screw-threaded end  80  of the thumbscrew  79  always performs its clamping action within the width of the depressible segment  74  and never touches either of the adjoining rigidly secured margins of the side member  71 . 
   For practical usefulness of the invention skywatcher&#39;s tripod, the extension arm  42 , even when extended as shown in  FIG. 6 , has to be able to positively lock the elevation of a surveillance device having a significant weight, at least 2.27 Kg (5 Lbs.). Since this weight is carried at the end of an extended arm, it obtains a considerable leverage at the holder&#39;s pivotal point  45 ,  FIGS. 6 and 9 . Location of the thumbscrew&#39;s axis  76 ,  FIG. 9 , radially spaced apart from the holder&#39;s pivot axis  45 , enables the thumbscrew  79  to obtain a better grip on the holder  43  than would be the case if the thumbscrew turned on the holder&#39;s pivot axis  45 . The illustrated configuration of the holder  43  such that its depressible segment  74  is spaced apart from the holder&#39;s pivot axis  45  is what makes it possible to locate the thumbscrew&#39;s axis  76  radially removed from the holder&#39;s pivot axis  45 . 
   The location of the holder  43  mounted between two parallel spaced apart lug members  47 ,  48 , makes it possible to use two thumbscrews aligned on the same axis  76  but in opposed relationship to each other so as to clamp the holder  43  between them, with the result that the strongest possible clamping action is obtained on the holder  43 , strong enough to positively prevent a carried elevated surveillance device from gradually slipping downwardly to an undesired lower elevation. As mentioned at the end of a paragraph above,  FIG. 6  shows a second screw-threaded hole  78  into which a second thumbscrew (not shown) may be turned. Spreading apart of one or both lug end portions  49 ,  50 ,  FIG. 9 , is prevented by provision of a screw or rivet  82  that fastens the end portions  49 ,  50 , together; the fastener passing through a spacer  83 ,  FIGS. 7 and 8 , that is positioned between the end portions  49 ,  50 , the spacer  83  having a length that ensures the proper spaced apart relationship between the end portions  49 ,  50 . 
   An extension spring  84 ,  FIG. 6 , has a lower end secured to a first shaft  85  that projects laterally from a side of the post member  26 , and has an upper end secured to a second shaft  86 ,  FIGS. 6 and 9 , that projects laterally from a lower end of the holder  43 ; the spring  84 ,  FIG. 6 , being connected in initial tension so as to counterbalance the weight of the extension arm  42  and at least some of the weight of any of the various surveillance devices that are likely to be carried by the extension arm  42 . 
   A boss  87 ,  FIG. 9 , located near the lower end  54  of the extension arm  42  is formed by a screw passed through a spacer. The boss  87  prevents unintended complete withdrawal of the extension arm  42  by impacting the first-encountered one of the spacers which are located between the side members  70 ,  71 , of the holder  43 . The rigidly secured margin  88 ,  FIG. 9 , of the holder  43  is made shorter in length than the likewise rigidly secured margin  89  in order to allow the extension arm  42  to be extended further before the boss  87  impacts the spacer/fastener indicated by the numeral  90  in  FIG. 6  that is securing the lower end of margin  88 ,  FIG. 9 , to the lower end of margin  91 ,  FIG. 6 . 
   As stated at the outset, the present disclosure is a Continuation-in-Part of an original application Ser. No. 11/483,363, filed Jul. 21, 2006. In that original disclosure, the tripod&#39;s post member is provided having its lower end pivotally secured so that the post member is adjustable to a forwardly leaning position as well as being positionable parallel to the swivel axis. This adjustability was provided in order to provide a seated user of the tripod with additional clearance between himself and the post member. Since that original filing date, field experience using prototypes has shown that such additional clearance is not critical; a more important consideration is maximum rigidity. Every movable joint in the construction creates a potential for shakiness, and so in the currently preferred embodiment the post member  26 ,  FIG. 9 , is rigidly fixed (preferably in perpendicular relationship for most compactness) to the main member  25  by means of first and second side plates  92 ,  93 , respectively, which, in this embodiment, are riveted to the post member  26  and to the main member  25 ; the side plates  92 ,  93 , also enhancing the rigidity of the main member  25  which, like the post member  26 , is made of square aluminum tubing. A cross-sectionally round steel shaft, indicated generally as  94 ,  FIG. 9 , concentric about the swivel axis  11  passes vertically through the main member  25  so that a lower end portion  95  of the shaft  94  depends from the main member  25 . In  FIG. 9 , the numeral  96  indicates only a circular top plate portion of the base which is indicted generally as  10  in  FIG. 6 ; the base  10 ,  FIG. 6 , having a corresponding bottom plate  97 . The three pairs of parallel spaced apart lugs, such as the lugs  15 ,  16 , in  FIG. 6 , between which the leg members such as leg member  13  are pivotally secured, are located between and are welded or bolted to the top and bottom plates  96 ,  97 ,  FIG. 6 .  FIG. 9  shows only the top plate  96  in order to fit the view on the sheet. It is to be understood that the lower portion  95 ,  FIG. 9 , of the steel shaft  94  is journaled in a first flanged bronze bearing  98 T,  FIG. 6 , that is press-fitted into an opening that is provided in the top plate  96  with the bore of the bearing concentric about the swivel axis  11 , and that the bottom plate  97 ,  FIG. 6 , is likewise provided with a second flanged bronze bearing  98 B but inverted so that the flange of bearing  98 B is positioned lowermost. The lower end portion  95 ,  FIG. 9 , of the steel shaft  94  is pivotally secured to the base  10 ,  FIG. 6 , by means of a cotter pin (not shown) that is passed through a hole  99 ,  FIG. 9 , that is drilled through the lowermost end of the steel shaft  94 , with a washer  100 ,  FIG. 6 , placed between the coffer pin and the flange of the lower bearing  98 B. The rider support structure  24  shown in  FIG. 9  is thereby understood to be positively secured to the base  10  which, in  FIG. 9 , is represented only by the circular top plate  96  portion of the base  10 . The partially sectioned away rearward end  38 ,  FIG. 9 , of the rider support  24  reveals that the steel shaft  94  is fixed to the aluminum main member  25  by passage through an eyebolt  101 ,  FIG. 9 , the screw-threaded end of which passes through a back plate  102  to which the eyebolt  101  is secured by means of a cap nut  103 . The rubber pad  29  serves to cushion the unfolded seat support member  28 . 
   The structure shown in  FIG. 9  includes a swivel lock that enables the user to almost instantly lock or release rotation of the rider support  24  about the swivel axis  11 ; it is a significant improvement over the swivel lock shown in the original disclosure which requires many turns of an elongate screw to jam it against the base on which the rider support swivels. As described above in a paragraph above, folding of the tripod disclosed herein requires a prerequisite particular alignment of the rider support  24  relative to the leg members,  12 ,  13 ,  14 , such that the forward end of the rider support  24  is centered between two of the leg members as shown in  FIGS. 7 and 8  so that the rearward end  38 ,  FIG. 8 , of the rider support  24  is aligned with the third one of the leg members. This alignment can suddenly change if the rider support  24  is free to swivel during the time the leg members are being lifted from their unfolded position to their folded position. To prevent loss of the desired alignment it is helpful to include a swivel lock, preferably one that is easy to engage and disengage in order that it will not become an annoying chore. Ease of use is also an advantage during skywatching when one wishes to instantly lock the rider support at a particular compass bearing, and it is advantageous to be able to do so while continuing to sight through the surveillance device in order not to lose the target. 
   The fixed attachment of the post member  26 ,  FIG. 9 , to the main member  25 , enables provision of an instantly engageable and disengageable swivel lock comprising an elongate steel rod, indicated generally as  104 ,  FIG. 9 , that is stiff but is capable of some degree of flexure. The steel rod  104  is pivotally secured to a lateral side of the main member section  25  of the rider support  24  for rotation about a rod pivot axis  105  that perpendicularly intersects the plane of symmetry near the swivel axis  11 , between same and the post member  26 . The steel rod&#39;s pivot axis  105  demarcates (A) a short rearward segment  106  of the rod  104  that extends from the rod&#39;s pivot axis  105  to a rearward terminal  107  of the rod  104  that is configured for depression against the top plate  96  of the base  10  and in the disengaged configuration of the rod  104  is positioned minimally spaced apart from the top plate  96  as is indicated in  FIG. 9  by the clearance indicated at  108 , and (B) a much longer forward segment  109  of the rod  104  that has a forward terminal  110  that is graspable by a seated user to enable pulling or pushing the forward segment  109  so as to pivot the rod  104  about the rod pivot axis  105 . A rod holding bracket  111  fixed to and extending laterally from the adjacent side of the post member  26  is provided with a first detent notch  112  that holds the forward segment  109  of the rod  104  in a forward position as shown in  FIG. 9  whereby the clearance  108  is maintained, and the rod holding bracket is provided with a second detent notch  113  that holds the forward segment  109  of the rod  104  in a rearwardly pulled position that lowers the rearward terminal  107  into frictional contact with the top plate  96  and simultaneously forces a flexure of the forward segment  109  so that the rearward terminal is jammed against the top plate  96  with a force that is great enough to stop rotation of the rider support  24  about the swivel axis  11 . The dashed lines  114  indicate this rearwardly moved alternative position of the forward segment  109  of the rod  104  which cannot be attained except by flexure of the forward segment  109 , whereby the resistance to flexure that is inherent in the steel rod holds the rearward terminal  107  forcibly jammed against the top plate  96  of the base  10 . Finally, the rod  104  is welded to a shaft  115 ,  FIG. 9 , that passes through the main member  25  and is pivotally secured thereto so that the shaft  115  defines the rod pivot axis  105 . The welded attachment of the rod  104  to the shaft  115  prevents lateral movement of the forward terminal  110  away from the post member  26  except by lateral flexure of the forward segment  109  so that the forward segment is always biased toward the post member  26  and therefore when the forward segment  109  is moved out of engagement with one notch, it is always biased to seek engagement with the other notch.