Abstract:
A simple self-contained, hand-held instrument for reading an azimuth or bearing in relation to the earth&#39;s magnetic field either out in the field or on the water with substantial accuracy. Means are provided that places the far object into the same focal plane (or focal point) as the close up bearings on the compass disc face, thus allowing the eye to instantly see both images without adjustment between near-sight and far-sight. Means are also provided for the adjustment of the instrument for the local variation or declination of the earth&#39;s magnetic field versus that of true north.

Description:
This application claims priority under 35 U.S.C. 119(e)(1) based on Applicants Provisional U.S. Patent Application Ser. No. 60/665,686 filed Mar. 28, 2005 and titled “HANDHELD OPTICAL MAGNETIC EARTH FIELD BASED BEARING DETERMINING INSTRUMENT”. 

   BACKGROUND OF THE INVENTION 
   1. Field 
   The invention lies in the field of orienteering, positioning and surveying instruments in general. More specifically, it refers to compass structure that allows a specific compass bearing to be identified with great accuracy, even for one with poor eyesight. More specifically the invention features a small handheld self-contained compass structure having a distant object viewing system and a compass face indicia viewing system, wherein the lines of sight of the two systems (lens sets) are in general alignment and wherein the focal points (on the viewers eye) for both systems are substantially coextensive, and whereby extremely rapid eye sighting from one line of sight to the other will not require any significant physiological change in the users eye lens. 
   2. Prior Art 
   There is considerable prior art in the area of sighting compasses, navigational instruments or peloris, and optical viewing instruments. There are commonly found small handheld instruments with open sights and mirrors to allow the compass bearing readings to be viewed. There are existing instruments that allow a magnified viewing of the compass bearing readings. However, these prior instruments lack accuracy because it is not possible to see the bearing information, both far and close, practically simultaneously without moving the head or unit and thus the body, and without refocusing of the viewers eye lens. 
   Also, there are more complicated units such as in U.S. Pat. No. 2,970,510 that magnify the compass bearing readings and insert them into the field of view of the far target. These instruments are complicated to construct and/or they block the viewing of the far target. Since it is essential that any magnetic disk type compass be held at a level position, having a part of the distance viewing blocked and not being able to tilt the compass to compensate can make it unusable in a field situation. Also, no teaching of creating a collaborative pair of sighting systems having the same focal point as in the present invention is present in any of the prior art. 
   There is not an instrument that both (a) leaves the field of view of the far target unobstructed, and (b) delivers to the observer corrected views of both the far and near target to the same focal plane or point, with magnification of the bearing readings for increased accuracy. Nor is there such an instrument that allow declination correction with accuracy and ease and an instrument with so few parts. Nor is there an instrument that can give accurate readings with such an ease of use and that can be as compactly constructed and at such a light weight for use by backpackers or others where weight is a big consideration. 
   Further, in conjunction with the present compass structure in a preferred embodiment with an object alignment mark on the separate, isolated far distance viewing system, and with magnification of the compass face viewing, it is possible to achieve an accuracy in measurement not available in any current handheld compass devices. One-half degree increments of markings of ⅛ inch in length and less and with similar spacings therebetween are easily discernable on an appropriate magnetic disk. 
   SUMMARY OF THE INVENTION 
   The weaknesses and disadvantages of the prior art instruments are overcome and the objectives of this invention are attained by an instrument in which there is a frame supporting a sighting means for far distance object viewing and a second sighting means for near distance viewing of a compass face with magnification, both sighting means focusing on one location where the eye of the observer is placed, and in conjunction with an each sighting means being separate and isolated from the appropriate disk type compass having a compass heading face for the near distance viewing, the operator can see both targets simultaneously. The eye simply looks slightly down or looks straight ahead, very rapidly. No movement of the device or head is necessary to attain proper alignment which can then be held steady for reading. 
   An angular adjustment to the compass body alignment mark (reading indica mark on clear compass cover) associated with the disk compass allows an easy correction for declination. Where local declination is extreme however, (plus 20 degrees or minus 20 degrees, for example) then the magnetic disk itself is angularly adjusted in appropriate increments, and the adjustment graph on the unit is changed to match. 
   OBJECTS AND ADVANTAGES 
   It is a primary object of this invention to provide a simple, inexpensive, self-contained compass unit that will provide information relative to the precise location of any object, particularly distant, relative to the position of the observer with an accuracy not obtainable by any other such hand-held unit. 
   It is a further object of this invention to have a device usable by a novice at the same high accuracy as an expert, including means for easily making a correction for declination. 
   It is a further object of this invention to have a device that is easily produced at a low cost. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other objects of the invention and an understanding of the details and principles of the invention will become evident from the following description, taken in conjunction with the appended drawings, in which the various structures are not drawn to scale or consistent proportions, and wherein: 
       FIG. 1  represents schematically the basis on which the instrument operates, showing a side view of one embodiment of an internal layout of the lensing, mirroring, and magnetic disk required to meet the various objects for this invention; 
       FIG. 2  shows a typical set of declination adjustment markings; 
       FIG. 3   a  represents a typical viewing in the field, with the upper view showing the field and target object (T), and the bottom view showing the magnified viewing of a compass disk set with zero degrees declination, and incorrectly reading exactly sixty degrees; 
       FIG. 3   b  represents a typical viewing in the field, with the upper view showing the field and target object and the bottom view showing the magnified viewing of a compass disk set with 6.5 degrees declination, and reading the correct 53.5 degrees. This correction for declination (the difference between true North and magnetic North) allows for accurate readings without calculating the results separately; 
       FIG. 4  represents a modification to the present unit where both the declination adjustment scale on the housing and the point of magnetic attraction on the disk magnetic north pole, normally the 0° mark) are both angularly moved twenty degrees, allowing additional compensation for declination in areas where the need for such exceeds twenty degrees. This would keep the zero degree mark on the compass cover  13  towards the center of the viewing area; 
       FIG. 5   a  represents a longitudinal cross-sectional view of a typical embodiment of this invention. 
       FIGS. 5   b  thru  5   f  show external views of the same ( 5   a ) housing from front, back, top, bottom and side with dimensions in inches; 
       FIG. 5   g  is a cross-sectional enlargement of the under bottom declination adjustment mechanism of  FIG. 5   d  taken generally along line  5   g - 5   g  in  FIG. 5   d;    
       FIG. 6  represents a detailed cross-sectional layout of the lensing and other optics for the preferred embodiment of this invention, including lens specifications and spacing. This is one of many possible combinations of lensing and the appropriate spacing for the optics chosen in which the goals of this invention may be met; and 
       FIG. 6A  shows the alignment markings on (B). 
   

   DESCRIPTION OF PREFERRED EMBODIMENT 
   Using a conventional disk magnetic compass or an equivalent of the same, two separate imaging systems allow focusing on (1) the target object or spot in the distance, and (2) the compass bearing of the hand held instrument. For the first objective four lenses and a vertical marker allow a corrected distant view. For the second objective a magnifying lens and small mirror allows a detailed viewing of a compass readout, with a movable reading mark correctable for declination. When declination exceeds twenty degrees at a location then a manufacturing modification is made to allow accurate adjustment for a specified area. 
     FIG. 1  is a basic schematic diagram of a typical embodiment of the invention. With the eye at the established location, two sets of optics allow the viewing of either set of information from the same location. In this embodiment, for the far view lens elements (A-D) allows the far view to be observed with the eye focused or adjusted for nearsighted viewing. A template or imager (B) is inserted to add a centerline indication to the viewfinder. A second line of sight is focused to the same location, with a magnifying lens (E) showing the image of a magnetic disk  24  thru a mirror  34 , also focused for close observation. The magnetic disk  24  is free floating on a shaft  11 , and surrounded by a liquid such as a light oil to dampen the movement of the disk. On the disk is printed, for example, a scale of 360 degrees in one degree increments. Over this disk is a clear cover  13  with an inscribed mark  58  on the cover edge which, in conjunction with the printed scale on the magnetic disk, allows the eye to read an exact heading (bearing). For this purpose the numerals and lettering on the compass disk are printed in mirror image, i.e., backwards. 
     FIG. 2  shows schematically a magnetic disk showing a portion of the 360° heading indicia, and the declination adjustment markings for plus or minus 30 degrees as viewed thru clear plastic window  55  marked by dotted line in  FIG. 5   b . However, with the pre-adjustment of the magnetic disk itself in specific increments this scale would be changed to match the magnetic adjustment. For instance, if the magnetic disk were adjusted for a plus twenty degrees, this scale might read from minus ten to plus fifty degrees, as shown in  FIG. 4 . These adjustment markings  17  on either the inside edge  59  or bottom side  19  of housing  26  allow the angular movement and setting of the inscribed mark P noted above to a varying location above the magnetic disk matching the necessary adjustment for local variation or declination of magnetic north with true north. 
   Referring further to the drawings and with particular reference to the claims herein, the present invention comprises a compass instrument  10  having structure for substantially simultaneously viewing a distant, e.g., 100 yards-100 mile away object  12  and a compass heading therefor with great accuracy without the need for eye refocusing, said structure comprising the components of a distant object sighting top lens set (viewing system)  16  having a distant viewing axis  18 , a compass indicia sighting bottom lens set  20  (viewing system) having an indicia viewing axis  22 , and a compass with magnetic disc  24  having peripheral heading indicia  14  thereon, said components being mounted in top-down order on a frame or housing  26  with said axes and the center  28  of said disc being in substantial symmetrical and vertical alignment in a vertical plane  30 , said viewing axes diverging from each other in said plane  30  at an angle “α” of from about 10° to about 30°, and said top and bottom lens sets giving substantially the same focal point whereby the viewers eye lens does not have to reconfigure to allow the viewer to clearly see the distant object and the compass heading indicia even though the viewers up and down eye movement cycle may occur at millisecond speeds. 
   Referring now to the example of  FIG. 3   b  a schematic diagram is shown in which a direction of travel is required as 53.5 degrees from the location of the user based on a horizontal angle in relation to true north. The user holds the unit close to his eye (stop surface  56  against cheek) and turns his/her body until the lower view (thru lens E) shows a compass heading of exactly 53.3 degrees from the true north direction. Then an exact line on the terrain is observed thru the upper imager (B) that corresponds with the center or viewing line (R) on (B) ( FIG. 6   a ). A target is then chosen that corresponds with this viewing line (R) and an exact point is chosen on that target. In this example the point would be the right side of the base (T 1 ) of the furthest tree (T). 
   As another example, using the same  FIG. 3   b  wherein an observer needs the exact angle from the observer&#39;s current location to the right side (T 1 ) of the base of the furthest tree (T), the observer sets the center line R of the upper viewer so that it intersects the target T 1 , then observes the compass heading on the lower viewer to within a half degree. 
   Both of the previous examples assume that the instrument has been preset/adjusted to the proper local magnetic declination for accurate results. 
     FIG. 4  shows a variation of the declination adjustment  21  showing from 10 to 50 degrees. This requires a remarking of the magnetic disk  24  for a variation of 20 degrees by rotating the markings on the magnetic disk accordingly. No variation of the simple method of operation of the unit is required, however viewing of accurate adjusted angles is possible where there are extreme variations in the earth&#39;s magnetic field versus true north. Various models can accommodate all spectrums of magnetic declination. 
   In  FIG. 6  exemplary lens sets and dimensions are shown as well as some preferred dimensions of the housing (frame)  26  and compass. The top lens set is provided by elements (A-D) having the configuration and dimensional specifications shown in the charts of  FIG. 6 , wherein “d” is the lens thickness on axis  18  and d 1  is the thickness on axis  22 . These lenses are set, e.g., by adhesive into supporting portions generally designated  32  of non-magnetic (plastic, brass, ceramic, etc.) frame  26  having a transparent or translucent section for lighted viewing. This is done by forming the housing  26  in clam shell type halves  45 ,  47  ( FIG. 5E ) preferably having notches  51  into which the edges of the lenses can fit as the halves are assembled. The halves are then adhesively or otherwise attached along the center cut line  53 . The distances between these lenses on axis  18  are noted in these charts in inches. 
   The focal point distance (FP) shown in  FIG. 6  of 1.45 inches to lens (A) from the viewers eye along axis  18  is a proven preferred one for the instrument as shown, however, depending on the designers objectives, other lens systems and housing structures can be employed as long as a comfortable focal point for the top and bottom two lens systems is effected. For example, (FP) can range from 0.5-2.0 in. Regarding the bottom lens (E), the specifications for lens (E) are given in the charts of  FIG. 6 . The angle of mirror face  34  from the horizontal is approximately 52° and the mirror is adhesively secured or the like at  35  to front end wall  40 . Lens (E) also is secured to portions  32  of the housing by adhesive or equivalent. 
   Referring to  FIGS. 5   d  and  5   g , a useful type of declination adjustment mechanism is shown wherein a portion of the housing wall  23  is removed to allow the body wall  25  of the compass to protrude into contact with an elastomeric roller  27  which is fixed to a circular shaft or armature  29  rotatably mounted in the housing base  31  and wall  23 . Armature  29  is rotatable in spacer  33  and the circular head  37  thereof is provided with a slot  39 . This slot can receive a screw driver or small coin edge or knife blade or the like for rotating the armature and roller to rotate the compass disc the required amount for the declination adjustment. 
   Referring to  FIG. 6 , the compass body  41  is snugly but rotatably mounted in recess  43  in the housing whereby the frictional compressive contact of body wall  25  with roller  27  will ordinarily fix the angular position of the compass within the housing until the roller is forcibly rotated by a screw driver or the like. 
   The housing or frame  26  is configured in the embodiment shown to provide a substantially enclosing structure having a top  36 , bottom  38 , front end wall  40 , rear end wall  42  and side walls  44 ,  46 . Wall  40  is apertured at  48  to provide a distant viewing forward port  49 , and wall  42  is apertured at  50  to provide an upper distant viewing port area represented by dotted line  52 , and a lower compass indicia viewing port area  54  represented by dotted line  54 . It is noted that the areas  52  and  54  and the viewing paths (axes)  18  and  22  which these areas serve are separate and distinct from each other, i.e., no occlusion of one by the other. 
   The invention has been described in detail with particular reference to preferred embodiments thereof, but it will be understood that variations and modifications will be effected with the spirit and scope of the invention.