Autofocus adapter

Abstract

An autofocus adapter is provided and includes an imaging adapter optical system placed on an optical axis of an imaging lens when the autofocus adapter is attached, and a focus state detection adapter optical system placed on an optical axis different from the optical axis of the imaging lens when the autofocus adapter is attached. The imaging adapter optical system has a light split prism for splitting subject light passing through the imaging lens into imaging subject light and the focus state detection subject light, a first lens group having a negative power as a whole and placed on the object side with respect to the light split prism, and a second lens group having a positive power as a whole and placed on the image side with respect to the light split prism. The focus state detection adapter optical system has a positive lens group having the same lens configuration as the second lens group in the imaging adapter optical system.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

The features of the invention will appear more fully upon consideration of the exemplary embodiment of the invention, which are schematically set forth in the drawings, in which:

FIG. 1 is a drawing to show a configuration of a camera system incorporating an autofocus adapter according to an exemplary embodiment of the invention;

FIG. 2 is a schematic representation to equivalently show the positional relationship between an imaging device for image formation and imaging devices for focus state detection on the same optical axis;

FIG. 3 is a block diagram to show a configuration of a signal processing section in an autofocus adapter according to an exemplary embodiment of the invention;

FIG. 4 is a schematic representation to show the principle of focus state detection in an autofocus adapter according to an exemplary embodiment of the invention;

FIG. 5 is an optical system sectional view to show a first configuration example of an adapter optical system in the autofocus adapter according to an exemplary embodiment of the invention;

FIG. 6 is an optical system sectional view to show a second configuration example of an adapter optical system in an autofocus adapter according to an exemplary embodiment of the invention;

FIG. 7 is a drawing to show one example of the lens data of an imaging lens;

FIG. 8 is a drawing to show the lens data of an adapter optical system according to example 1 in an autofocus adapter according to an exemplary embodiment of the invention;

FIG. 9 is a drawing to show the lens data of an adapter optical system according to example 2 in an autofocus adapter according to an exemplary embodiment of the invention;

FIG. 10 is a drawing to show the lens data of an adapter optical system according to example 3 in an autofocus adapter according to an exemplary embodiment of the invention;

FIG. 11 is a drawing to show the lens data of an adapter optical system according to example 4 in an autofocus adapter according to an exemplary embodiment of the invention; and

FIG. 12 is a drawing to show the values concerning conditional expressions collectively about the examples.

Claims

1. An autofocus adapter being placed detachably between an imaging lens and a camera main body and detecting a focus state of the imaging lens and performing autofocus control of the imaging lens, the autofocus adapter comprising: a first optical system placed on a first optical axis of the imaging lens;a second optical system placed on a second optical axis different from the first optical axis; andan imaging device receiving first subject light for detecting the focus state of the imaging lens, through the second optical system,wherein the first optical system comprising:a first light split unit being placed on the first optical axis and splitting subject light, which is passed through the imaging lens, into the first subject light and second subject light for image formation;a first lens group having a negative power and placed on an object side with respect to the first light split unit; anda second lens group having a positive power and placed on an image side with respect to the first light split unit.

2. The autofocus adapter according to claim 1, wherein the first optical system satisfies Conditional Expression: 1.0<d/2h   (1)

3. The autofocus adapter according to claim 2 wherein the first lens group comprises a first cemented lens comprising a negative lens and a positive lens,the second lens group comprises a positive lens and a second cemented lens, the second cemented lens comprising a positive lens and a negative lens, andthe first optical system satisfies Conditional Expression: −0.8<f1/f2<−0.7   (2)

4. The autofocus adapter according to claim 3, wherein the first light split unit comprises right-angle prisms cemented on slopes thereof, and wherein the first light split unit has a light split face placed at an angle of approximately 45° with respect to the first optical axis and emits the first subject light in a bend direction of approximately 90° with respect to the first optical axis.

5. The autofocus adapter according to claim 4, wherein the second optical system is placed on an emission side of the first subject light relative to the first light split unit, and wherein the second optical system comprises a positive lens group having the same lens configuration as in the second lens group of the first optical system.

6. The autofocus adapter according to claim 5, wherein the second optical system further comprises a right-angle prism that bends approximately 90° an optical path of the first subject light passed through the positive lens group.

7. The autofocus adapter according to claim 6, wherein the second optical system further comprises a second light split unit placed on the optical path bent by the right-angle prism and splitting the optical path of the first subject light into a plurality of optical paths, and wherein the imaging device is placed on each of the plurality of optical paths.

8. The autofocus adapter according to claim 3, wherein the second optical system is placed on an emission side of the first subject light relative to the first light split unit, and wherein the second optical system comprises a positive lens group having the same lens configuration as in the second lens group of the first optical system.

9. The autofocus adapter according to claim 2, wherein the first light split unit comprises right-angle prisms cemented on slopes thereof, and wherein the first light split unit has a light split face placed at an angle of approximately 45° with respect to the first optical axis and emits the first subject light in a bend direction of approximately 90° with respect to the first optical axis.

10. The autofocus adapter according to claim 9, wherein the second optical system is placed on an emission side of the first subject light relative to the first light split unit, and wherein the second optical system comprises a positive lens group having the same lens configuration as in the second lens group of the first optical system.

11. The autofocus adapter according to claim 2, wherein the second optical system is placed on an emission side of the first subject light relative to the first light split unit, and wherein the second optical system comprises a positive lens group having the same lens configuration as in the second lens group of the first optical system.

12. The autofocus adapter according to claim 1, further comprising: a detection unit detecting the focus state of the imaging lens based on an image captured by the imaging device; anda control unit performing autofocus control of the imaging lens based on the focus state.

13. The autofocus adapter according to claim 1 wherein the first lens group comprises a first cemented lens comprising a negative lens and a positive lens,the second lens group comprises a positive lens and a second cemented lens, the second cemented lens comprising a positive lens and a negative lens, andthe first optical system satisfies Conditional Expression: −0.8<f1/f2<−0.7   (2)

14. The autofocus adapter according to claim 13, wherein the first light split unit comprises right-angle prisms cemented on slopes thereof, and wherein the first light split unit has a light split face placed at an angle of approximately 45° with respect to the first optical axis and emits the first subject light in a bend direction of approximately 90° with respect to the first optical axis.

15. The autofocus adapter according to claim 14, wherein the second optical system is placed on an emission side of the first subject light relative to the first light split unit, and wherein the second optical system comprises a positive lens group having the same lens configuration as in the second lens group of the first optical system.

16. The autofocus adapter according to claim 15, wherein the second optical system further comprises a right-angle prism that bends approximately 90° an optical path of the first subject light passed through the positive lens group.

17. The autofocus adapter according to claim 16, wherein the second optical system further comprises a second light split unit placed on the optical path bent by the right-angle prism and splitting the optical path of the first subject light into a plurality of optical paths, and wherein the imaging device is placed on each of the plurality of optical paths.

18. The autofocus adapter according to claim 13 wherein the second optical system is placed on an emission side of the first subject light relative to the first light split unit, and wherein the second optical system comprises a positive lens group having the same lens configuration as in the second lens group of the first optical system.

19. The autofocus adapter according to claim 1, wherein the first light split unit comprises right-angle prisms cemented on slopes thereof, and wherein the first light split unit has a light split face placed at an angle of approximately 45° with respect to the first optical axis and emits the first subject light in a bend direction of approximately 90° with respect to the first optical axis.

20. The autofocus adapter according to claim 19, wherein the second optical system is placed on an emission side of the first subject light relative to the first light split unit, and wherein the second optical system comprises a positive lens group having the same lens configuration as in the second lens group of the first optical system.

21. The autofocus adapter according to claim 20, wherein the second optical system further comprises a right-angle prism that bends approximately 90° an optical path of the first subject light passed through the positive lens group.

22. The autofocus adapter according to claim 21, wherein the second optical system further comprises a second light split unit placed on the optical path bent by the right-angle prism and splitting the optical path of the first subject light into a plurality of optical paths, and wherein the imaging device is placed on each of the plurality of optical paths.

23. The autofocus adapter according to claim 1, wherein the second optical system is placed on an emission side of the first subject light relative to the first light split unit, and wherein the second optical system comprises a positive lens group having the same lens configuration as in the second lens group of the first optical system.

24. The autofocus adapter according to claim 23, wherein the second optical system further comprises a right-angle prism that bends approximately 90° an optical path of the first subject light passed through the positive lens group.

25. The autofocus adapter according to claim 24, wherein the second optical system further comprises a second light split unit placed on the optical path bent by the right-angle prism and splitting the optical path of the first subject light into a plurality of optical paths, and wherein the imaging device is placed on each of the plurality of optical paths.