Device for adjusting axial position of lens

A device for adjusting an optical axial position of a lens is disclosed. The device includes a lens frame for mounting at least one lens, a lens frame supporting member rotatably engaged with the lens frame via screw threads for supporting the lens frame in such a way that the lens frame is rotatable relative to the lens frame supporting member, coupled to a stationary member for adjustment of the optical axial position of the lens relative to the stationary member. Set screws are provided for selectively locking the lens frame to the lens frame supporting member at one of a plurality of stepwise, predetermined, relative angular positions between the lens frame and the lens frame supporting member after the optical axial position of the lens has been adjusted relative to the lens frame supporting member. Since the lens frame can be locked to the lens frame supporting member at one of the plurality of stepwise, predetermined, relative angular positions by use of the set screws after the optical axial position of the lens has been adjusted, it is possible to improve the locking reliability and simplify the structure of the adjusting device.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a device for adjusting the optical axial position 
of a lens, and more specifically to a device for adjusting the position of 
a lens in the optical axial direction thereof when the lens is assembled 
and adjusted into a complete optical unit. 
2. Description of the Prior Art 
When the lens or lenses are assembled into an optical unit, the position of 
a lens mounted in a lens barrel must be adjusted in the optical axial 
direction thereof, for effecting infinite focus distance adjustment, 
zooming adjustment, back focus distance adjustment, and the like. The lens 
barrel normally has a cylindrical stationary member to be coupled to a 
body of the optical unit, a lens frame supporting member coupled to the 
stationary member through helicoidal threads, and a lens frame to which a 
lens is to be mounted and which is coupled to the lens frame supporting 
member through screw threads. 
The most conventional way of adjusting the optical axial position of the 
lens, is to extend or retract the lens frame axially relative to the lens 
frame supporting member, whenever the lens frame is rotated with respect 
to the lens frame supporting member. 
In the above-mentioned method, it is possible to adjust the axial position 
of the lens continuously or steplessly relative to the lens frame 
supporting member by adjusting the amount of the thread engagement between 
the lens frame and the lens frame supporting member. After being adjusted, 
the lens position must be locked by means of an appropriate locking 
mechanism. 
Conventionally, various lens frame locking mechanisms have so far been 
adopted as follows: 
In a first example, a lens is mounted on a lens frame, the lens frame is 
engaged via screw threads with a lens frame supporting member (e.g., 
focusing ring), and the lens frame supporting member is coupled to a 
stationary member through helicoidal threads. After the lens frame has 
been adjusted relative to the lens frame supporting member by adjusting 
the amount of the thread engagement between the lens frame and the lens 
frame supporting member, a spacer washer having a selected thickness is 
sandwiched between a flange of the lens frame supporting member and a 
flange of the lens frame. Thereafter the lens frame is tightly screwed 
against the lens frame supporting member to lock the lens frame to the 
lens frame supporting member. 
In this first example, however, there exist problems which result from the 
fact that the thickness of the spacer washer must be carefully selected 
and the lens frame must be removed from the lens frame supporting member 
before sandwiching the selected spacer washer between those two parts. 
In a second example, after the lens frame has been adjusted relative to the 
lens frame supporting member in such a manner as stated above, the lens 
frame is locked by use of an additional locking unit. The additional 
looking unit is a locking nut which is to be screwed to an inner thread 
formed in the lens frame supporting member, whereby the rotational 
movement of the lens frame with respect to the lens frame support member 
is restricted by fastening the locking nut against the lens frame. 
In this second method, however, there exist other problems. Namely, a 
special jig is required to screw the locking nut. As a result, the lens 
frame is likely to be dislocated or the lens is likely to be scratched 
when the locking nut is fastened too tightly toward the lens frame. 
In a third example, after the lens frame has been adjusted relative to the 
lens frame supporting member, the lens frame is fixed to the lens frame 
supporting member by screwing a set screw or set screws from the outer 
circumferential surface of the lens frame supporting member to the lens 
frame in the radial direction of the lens. 
Again, problems exist as a result of using the third method. Namely, the 
lens frame or the lens frame supporting member is likely to be deformed 
when the set screws are fastened too tightly. 
SUMMARY OF THE INVENTION 
With these problems in mind, it is therefore the primary object of the 
present invention to provide a device for adjusting the optical axial 
position of a lens mounted on a lens frame with respect to a lens 
supporting member, which is simple in structure, yet highly accurate in 
adjusting precision, and excellent with regard to locking reliability. 
To achieve the above-mentioned object, a device for adjusting the optical 
axial position of a lens according to the present invention, includes a 
lens frame for mounting the lens; a lens frame supporting member having 
two ends, at least one lens frame supporting member being at one end 
thereof to be coupled to a stationary member and at the other end thereof 
rotatably engaged with the lens frame via screw threads for supporting the 
lens frame in such a way that the lens frame is rotatable relative to the 
lens frame supporting member for adjusting the optical axial position of 
the lens relative to the stationary member; and means for selectively 
locking the lens frame to the lens frame supporting member at one of a 
plurality of stepwise, predetermined, relative angular positions between 
the lens frame and the lens frame supporting member after the optical 
axial position of the lens has been adjusted relative to the lens frame 
supporting member by adjustably rotating the lens frame with respect to 
the lens frame support member. 
The conceptual basis of the present invention results from the fact that it 
is possible to realize a lens axial position adjusting device which has a 
simple structure and excellent locking reliability even when the optical 
axial position of the lens is adjusted in stepwise fashion. In addition, 
the present invention is free from problems with respect to adjustment 
precision even though the optical axial position of the lens is adjusted 
in stepwise fashion. 
In the lens axial position adjusting device according to the present 
invention, the optical axial position of the lens mounted on the lens 
frame can be adjusted by rotating the lens frame relative to the lens 
frame supporting member. After the optical axial position of the lens has 
been adjusted, the lens frame is locked with the lens frame supporting 
member by the selective locking means at one of the plurality of stepwise, 
predetermined angular positions between the lens frame and the lens frame 
supporting member. The selective locking means is preferably composed of 
set screws, tapped holes formed in the lens frame, and a plurality of lock 
recesses formed in the lens frame supporting member. The screws are 
adapted to be engaged with any of the lock recesses through the tapped 
holes at or in the close vicinity of the adjusted position between the 
lens frame and the lens frame supporting member. 
Therefore, since the lens frame can be locked to the lens frame supporting 
member at one of the stepwise, predetermined, relative angular positions 
by means of the set screws, after the lens frame has been adjustably 
rotated relative to the lens frame supporting member to complete 
adjustment of the optical axial position of the lens, it is possible to 
simplify the structure of the device and improve the locking reliability 
without deteriorating the adjusting precision. 
According to the present invention, a preferred embodiment has 45 lock 
recesses arranged on the lens frame supporting member along the 
circumferential direction thereof at 8 degree intervals. There are three 
tapped holes arranged on the lens frame along the circumferential 
direction thereof at 120 degree intervals, such that the three holes mate 
with any of three recesses of the lens frame supporting member.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Embodiments of the device according to the present invention will be 
described hereinbelow with reference to the attached drawings. 
FIG. 1 shows a first embodiment which is applied to a device for adjusting 
the optical axial position of a group of focusing lenses L1 mounted on the 
frontmost position of a lens barrel 10. The lens barrel 10, which is to be 
coupled to a body of an optical unit, includes a lens frame 11 having a 
lens mounting member 12 and a lens retaining member 13 by which the lenses 
L1 are mounted; a substantially cylindrical lens frame supporting member 
(focusing ring) 15; and a substantially cylindrical stationary member 14. 
The lens mounting member 12 of the lens frame 11 engages with the focusing 
ring 15 through single fine threads 18. The focusing ring 15 engages with 
the stationary member 14 via helicoidal threads 16. The lens frame 11 to 
which the lenses L1 are mounted is locked to the focusing ring 15 after 
the optical axial position of the lenses L1 has been adjusted relative to 
the focusing ring 15 by rotating the lens frame 11 with respect to the 
focusing ring 15 via the single fine screw threads 18. 
Specifically, the focusing lenses L1 are fixedly bonded between the lens 
mounting member 12 and the lens retaining member 13. The lens mounting 
member 12 has a cylindrical portion, and an extra small, single, male 
screw thread 18a is formed on the outer circumferential surface of the 
cylindrical portion. The focusing ring 15 has an inwardly extending flange 
20 having an inner circumferential surface and located around the 
cylindrical portion of the lens mounting member 12. An extra small, 
single, female screw thread 18b is formed on the inner circumferential 
surface thereof so as to engage with the male screw thread 18a of the lens 
mounting member 12. Further, the focusing ring 15 is formed with female 
helicoidal threads 16b on the inner circumferential surface thereof. The 
stationary member 14 is formed with male helicoidal threads 16a on the 
outer circumferential surface thereof so as to engage with the female 
helicoidal threads 16b of the focusing ring 15. 
On the front end surface of the inwardly extending flange 20 of the 
focusing ring 15 (left side in FIG. 1), there are formed a plurality of 
lock recesses or grooves 21, as depicted in FIG. 2. In this embodiment, 45 
lock recesses 21, each of which has a U-shaped configuration extending in 
the radial direction of the focusing ring 15 and recessed in the axial 
direction thereof, are arranged at regular 8 degree angular intervals in 
the front end surface of the focusing ring 15 along the circumferential 
direction thereof, as is partially shown in FIG. 3. 
Further, the lens retaining member 13 is provided with an inwardly 
extending flange 22 so as to face the flange 20 of the focusing ring 15 
when assembled. In the extending flange 22 of the lens retaining member 
13, there are formed a plurality of tapped holes 23h (shown in FIG. 2). In 
this embodiment, 3 tapped holes 23h, each of which extends in the axial 
direction of the lens frame 11, are arranged at regular 120 degree angular 
intervals in the flange 22 of the lens retaining member 13 along the 
circumferential direction thereof. Several set screws 23 (for example, 3) 
are screwed into the tapped holes 23h formed in the flange 22 of the lens 
retaining member 13, as shown in FIG. 4. The angular positions of these 
tapped holes 23h are determined so as to match the arrangement positions 
of the lock recesses 21. In other words, the mutual, angular, positional 
relationship between the tapped holes 23h and the lock recesses 21 is 
determined in such a way that the set screws 23 can enter the lock 
recesses 21 through the tapped holes 23h at any angular position. 
Furthermore, the set screws 23 are arranged in such positions so as to be 
fastenable from the front side (left side in FIG. 1) of the lens frame 11. 
The focusing ring 15 formed with plural lock recesses 21 is preferably 
manufactured by molding resin material, because molded parts are easy to 
manufacture and have high dimensional precision. 
The procedure of adjusting the optical axial position of the lenses L1 will 
be described hereinbelow. 
First, the focusing ring 15 is set or assumed to be set to a predetermined 
position (e.g., infinite focus distance) relative to the stationary member 
14 through the helicoidal threads 16. Thereafter, the optical axial 
position of the lens frame 11 is adjusted relative to the stationary 
member 14 or a fixed position (such as a certain position on a film plane) 
by adjustably rotating the lens frame 11 relative to the focusing ring 15, 
under the condition that the set screws 23 are not projected from the rear 
(right side in FIG. 1) end surface of the inner flange 22 of the lens 
retaining member 13 toward the lock recesses 21 of the focusing ring 15. 
In this procedure, it is possible to adjust the optical axial position of 
the lenses L1 by using a collimator as a guide, for example. 
After the lens position has been adjusted, the set screws 23 are fastened 
into the lock recesses 21. At this moment, the positions of the set screws 
23 may not match the positions of the lock recesses 21. In this case, the 
lens frame 11 may be rotated (e.g., less than the angular pitch [8 
degrees, in this embodiment] of the lock recesses 21) in either of the 
clockwise or counter clockwise direction in order to match the set screws 
23 with the lock recesses 21, before the set screws 21 are fastened into 
the lock recesses 21 and against the focusing ring 15. Under these 
conditions, since the lens frame 11 can be fixed to the focusing ring 15, 
the adjustment of the optical axial position of the lens group L1 is 
completed. 
Thereafter, it is preferable to attach a sealing member 25 on the front end 
surface of the inner flange 22 of the lens retaining member 13 to cover 
the tapped holes 23h. 
The adjustment or regulation precision of the present invention will be 
discussed below. When the lock recesses 21 are arranged at regular angular 
intervals of 8 degrees (i.e., when there are 45 lock recesses 21) and the 
pitch of the single screw threads 18 is 0.5 mm, the lens frame 11 is 
shifted in the optical axial direction thereof by 0.011 mm whenever the 
lens frame 11 is rotated relative to the focusing ring 15 from one lock 
recess 21 to another adjacent lock recess 21. This relationship is 
represented by the following formula: 
EQU (8 degrees/360 degrees).times.0.5 mm.apprxeq.0.011 mm 
This shift rate is sufficient for the precision required when an ordinary 
lens focus is adjusted. For example, the assumption made is that the lens 
is a zoom lens whose focal distance is 49 mm for the ordinary objective 
and 80 mm for the telephoto objective. In this case, the square of the 
ratio of the telephoto focal distance to the ordinary focal distance is 
(80/49).sup.2 =2.7 
Therefore, the deviation error of the focal distance on the film (i.e., 
screen) plane is at the worst: 
EQU 0.011 mm.times.2.7.apprxeq.0.03 mm 
This value is also negligible and therefore can be disregarded in the 
adjustment of the optical axial position of the zoom lens. 
FIG. 4 shows another embodiment of the present invention, in which an 
additional three tapped holes are formed at regular angular intervals in 
the inner flange 22 of the presser ring 13, and three set screws 23S are 
screwed into these additional tapped holes. The additional set screws 23S 
are arranged with respect to the set screws 23 at a phase difference of 
1/2 of the angular pitch (8 degrees) of the lock recesses 21 (i.e., 4 
degrees). Thus, in the embodiment shown in FIG. 4, each of the additional 
three set screws 23S is offset by an offset angle of 4 degrees from each 
of the three set screws 23, respectively. As a result, according to this 
embodiment, it is possible to obtain a more precise adjustment for the 
optical axial position of the lenses. 
Specifically, in this embodiment, only one group of set screws 23 or 23S is 
used for locking the lens frame 11 to the focusing ring 15, without the 
need to use all the six set screws. Since the additional group of phase 
shifted set screws 23S can be used, it is possible to reduce by half the 
regulating angular pitch of the lens frame 11 relative to the focusing 
ring 15, as compared with the first embodiment. 
In general, if the angular pitch of the lock recesses 21 is B degrees and 
the axial pitch of the single screw threads 18 between the lens frame 11 
and the focusing ring 15 is P mm, it is possible to stepwise adjust the 
optical axial position of the lens L1 by a step of (B degrees/360 
degrees).times.P mm. 
Still further an additional group of set screws 23S can be arranged in 
relation to the set screws 23 with a phase difference of 1/N.times.B 
degrees (the angular pitch of the lock recesses), where N denotes an 
integer greater than or equal to two. 
When the additional set screws 23S are used, it is possible to further 
reduce by 1/N the regulating or adjusting angular pitch of the lens frame 
11 relative to the focusing ring 15, as compared with the first 
embodiment. 
In the above-mentioned embodiments, 45 lock recesses are formed on the 
focusing ring 15 and 6 tapped holes, including the additional phased 
holes, are formed on the lens retaining member 13. However, according to 
the present invention, it is also possible to form 45 tapped holes on the 
focusing ring and 6 lock recesses on the lens retaining member 13, vice 
versa. 
Further, in the above-mentioned embodiments, the set screws 23 are fastened 
in the direction parallel to the optical axis of the lens L1. Without 
being limited thereto, however, it is also possible to form the lock 
recesses or grooves on the outer circumferential surfaces of the focusing 
ring 15 and form tapped holes in the outer circumferential surface of the 
lens retaining member 13 in such a way that the set screws can be fastened 
from the outside of the lens retaining member 13 in the radial direction 
thereof, as illustrated by the dotted line in FIG. 1. In this case, it is 
preferable that each of the tapped holes in the lens retaining member 13 
be formed into an elongated configuration in the axial direction of the 
lens retaining member in order to absorb any axial displacement of the 
lock recesses of the focussing ring 15 resulting from the threading motion 
thereof. 
Finally, in the above-mentioned embodiments, the present invention has been 
described with respect to its application to a device for adjusting the 
optical axis position of a focusing lens. Without being limited thereto, 
however, it is of course possible to apply the device of the present 
invention to adjust the optical axial positions of any other lenses. 
As described above, in the device for adjusting the optical axial position 
of a lens according to the present invention, the lens frame (presser 
ring) is rotated relative to the lens frame supporting member (focusing 
ring) in a stepwise manner for adjusting the optical axial position of the 
lens and then locked to the lens frame supporting member at one of the 
stepwise, predetermined, relative angular positions. Thereafter, by 
driving the set screws through the tapped holes formed in the lens frame 
into the lock recesses or grooves formed in the lens frame supporting 
member, it is possible to adjust the optical axis position of the lens 
simply and reliably, without deteriorating the adjustment or regulation 
precision. 
Finally, it should be noted that the present disclosure relates to subject 
matter contained in Japanese Patent Application No. 3-214849 filed on May 
20, 1991 which is expressly incorporated herein by reference in its 
entirety.