Real image viewfinder requiring no field lens

• US 5,241,337 A
• Filed: 05/13/1991
• Issued: 08/31/1993
• Est. Priority Date: 05/13/1991
• Status: Expired due to Fees

• Current Assignee: Eastman Kodak Company
• Original Assignee: Eastman Kodak Company
• Inventors: Betensky, Ellis I., Ruben, Paul L.
• Primary Examiner(s): Gray, David M.
• Application Number:
  US07/699,284
• Time in Patent Office: 841 Days
• Field of Search: 354/219-225, 359/643-647, 359/676-678
• US Class Current: 396/382
• CPC Class Codes: G02B 15/143507 arranged -++
• CPC Class Codes: G02B 23/14 Viewfinders for photographic apparatus G03B13/02
• CPC Class Codes: G02B 23/145 Zoom viewfinders
• CPC Class Codes: G03B 13/12 to compensate for change of camera lens or size of picture

Abstract

A real image zooming viewfinder comprising three optical units with refracting optical power and an additional moving reflective optical unit. Zooming is accomplished by moving one of the refractive optical units and the additional reflective optical unit or by moving the first and the second optical units. The need for field lens is eliminated by having the first and the second unit cooperate to make the finder system telecentric with respect to principal rays at the intermediate image plane.

Claims

1. In an optical finder system without presence of a field lens having a field of view in object space of a half angle of at least 2°

as defined by the principal rays the finder system including a reflective optical assembly including, a plurality of reflective surfaces;

first and second optical units for forming a real image at an intermediate image plane in the reflective optical assembly;

an eyelens to facilitate viewing of an object; and

wherein the improvement comprises;

said first and said second optical units cooperate to make said principal rays substantially parallel to an optical axis at the intermediate image plane.

2. An optical finder system according to claim 1 wherein the first optical unit has negative optical power and the second optical unit has positive optical power.

3. An optical finder system according to claim 2, wherein the second optical unit moves along the optical axis for zooming as a variator to effect a magnification change, and optical elements of the reflective optical assembly move during zooming as a compensator.

4. An optical finder system according to claim 2 wherein the first optical unit moves along the optical axis during zooming to compensate for the movement of the second optical unit during zooming.

5. An optical finder system according to claim 2 in which the first lens element is moved laterally to provide for parallax correction for focusing on close objects.

6. An optical finder system according to claim 1 further comprising a three-dimensional field mask, said mask having a thickness substantially equal to the size of an image drift between optical elements of said reflective optical assembly.

7. An optical finder system according to claim 2 further comprising a three-dimensional field mask, said mask having a thickness substantially equal to a size of an image drift between optical elements of said reflecting assembly.

8. An optical finder system according to claim 1 in which all lens elements having refractive power are made from a same material.

17. An optical finder system according to claim 1, wherein radii of surface aspheric coefficients, the thickness of the elements and the optical materials are as follows:

space="preserve" listing-type="tabular">______________________________________ MATERIAL RADIUS THICKNESS TYPE ______________________________________ First lens element -85.988 1.00 acrylic 4.933 (3) varies Second lens element 13.759 2.50 acrylic -7.959 (4) varies 30.18 Third lens element 25.240 (5) 3.00 acrylic -12.443 22.39 ______________________________________ POLYNOMIAL ASPHERES (COEFFICIENTS OF THE EVEN POWERED TERMS) NO. D (4th) E (6th) F (8th) ______________________________________ (3) 1.3882E - 03 1.5508E - 05 -9.3330E - 06 (4) 8.6265E - 04 -1.3786E - 04 2.1750E - 05 (5) -7.1589E - 05 -3.2260E - 06 1.5573E - 08 ______________________________________ NO. G (10th) H (12th) I (14th) ______________________________________ (3) 4.2796E - 07 6.9955E - 08 5.6732E - 09 (4) -1.0064E - 06 -5.6207E - 08 4.3911E - 09 (5) 1.5367E - 09 5.6142E - 12 -8.8297E - 13 ______________________________________

18. An optical finder system according to claim 1, wherein radii of surface aspheric coefficients, the thickness of the elements and the optical materials are as follows:

space="preserve" listing-type="tabular">______________________________________ MATERIAL RADIUS THICKNESS TYPE ______________________________________ Lens element 10'"'"' -24.1866 1.00 acrylic 14.2806 (3) varies Lens element 20'"'"' 11.6342 2.70 acrylic -13.2610 (4) varies Lens element 40'"'"' 92.0099 3.10 acrylic -10.7746 (5) 22.24 ______________________________________ (1) (2) Zoom space. Refer to ZOOM DATA TABLE. (3) (4) (5) Aspherical surface. Sag is defined per following formula;

##STR3## - where 1/C is radius of curvature for the surface, and K is the conic constant of the surface,

space="preserve" listing-type="tabular">______________________________________ POLYNOMIAL ASPHERES (COEFFICIENTS OF THE EVEN POWERED TERMS) NO. D (4th) E (6th) F (8th) ______________________________________ 3 -6.6976E - 04 3.0536E - 05 -2.0633E - 06 4 6.9506E - 05 -2.2428E - 05 2.6700E - 06 5 -7.7865E - 06 1.4656E - 06 -6.9094E - 08 ______________________________________ NO. G (10th) H (12th) I (14th) ______________________________________ 3 3.1544E - 08 2.6902E - 09 -7.8763E - 11 4 -6.5908E - 08 -2.5406E - 09 9.6469E - 11 5 -1.2694E - 10 3.3673E - 11 -2.9428E - 13 ______________________________________ CONIC CONSTANTS NO. VALUE ______________________________________ 2 -5.81581E - 01 4 -6.59321E + 00 6 -1.28134E + 00 ______________________________________

9. In an optical finder system having a field of view including a first and a second optical unit which together cooperate for forming a real image in a reflective optical assembly, said reflective optical assembly including a plurality of optical elements having reflective surfaces, and an eyelens to facilitate the viewing of the object;

wherein the improvement comprises;

the first and the second optical units cooperating to make the finder system substantially telecentric with respect to said principal rays at an intermediate image plane.

10. An optical finder system according to claim 9 wherein the first optical unit has negative optical power and the second optical unit has positive optical power.

11. An optical finder system according to claim 10, wherein the second optical unit moves along the optical axis for zooming as a variator to effect a magnification change, and the optical elements of the reflective optical assembly move during zooming as a compensator.

12. An optical finder system according to claim 10 wherein the first optical unit moves along the optical axis during zooming to compensate for the movement of the second optical unit during zooming.

13. An optical finder system according to claim 10 in which a first lens element is moved laterally to provide for parallax correction for focusing on close objects.

14. An optical finder according to claim 10 further comprising a three-dimensional field mask, said mask having a thickness substantially equal to the size of an image drift between optical elements of said reflective optical assembly.

15. An optical finder system according to claim 9 further comprising a three-dimensional field mask, said mask having a thickness substantially equal to the size of an image drift.

16. An optical finder system that does not have a field lens, the system consisting of three optical units each having optical power, the system having only three lens elements with refractive optical power and an additional reflective erecting assembly for erecting an image of an object, said optical units being a first negative optical unit, a second positive optical unit which moves to effect a magnification change and to form a real image, and a third positive optical unit used to view said real image, wherein said first and said second optical units cooperate to make principal rays substantially parallel to an optical axis at an intermediate image plane.

19. In an optical finder system without presence of a field lens, the finder system including a reflective optical assembly including, a plurality of reflective surfaces;

first and second optical units for forming a real image at an intermediate image plane in the reflective optical assembly;

an eyelens to facilitate viewing of an object; and

wherein the improvement comprises;

said first and said second optical units cooperate to make principal rays substantially parallel to an optical axis at the intermediate image plane, said first optical unit having negative optical power and said second optical unit having positive optical power.

20. An optical finder system according to claim 19 wherein said first optical unit moves along the optical axis during zooming to compensate for the movement of said second optical unit during zooming.

21. An optical finder system according to claim 20 in which first lens element is moved laterally to provide for parallax correction for focusing on close objects.