Image-taking lens apparatus

1. An image-taking lens apparatus comprising:

an image sensor for converting an optical image of a subject into an electrical signal; and

an image-taking lens system for forming the optical image on the image sensor, the image-taking lens system including a prism configured to bend an optical path approximately 90 degrees,

wherein the prism fulfills the following conditional formula:

Ndp>1.9

where

Ndp represents a refractive index for a d-line of the prism.

2. An image-taking lens apparatus as claimed in claim 1 ,

wherein the image-taking lens system is a variable-focal-length imaging optical system.

3. An image-taking lens apparatus as claimed in claim 1 ,

wherein the image-taking lens system includes at least one negative lens element on an object side of the prism.

4. An image-taking lens apparatus as claimed in claim 1 ,

wherein the image-taking lens system includes an aperture stop or a shutter on an image side of the prism.

5. A zoom lens system that includes a plurality of lens units and that achieves zooming by varying distances between the lens units, the zoom lens system comprising:

a prism for bending an optical path,

wherein the prism fulfills the following conditional formula:

Ndp>1.9

where

Ndp represents a refractive index for a d-line of the prism.

6. A zoom lens system as claimed in claim 5 ,

wherein the prism reflects a light beam in such a way as to bend the optical path at approximately 90 degrees.

7. A zoom lens system as claimed in claim 5 , further comprising:

at least one negative lens element disposed on an object side of the prism.

8. A zoom lens system as claimed in claim 5 ,

wherein the prism is included in a most object-side lens unit

9. A zoom lens system as claimed in claim 8 ,

wherein the most object-side lens unit includes at least one lens element on the image side of the prism.

10. A zoom lens system as claimed in claim 9 ,

wherein the most object-side lens unit includes at least one positive lens element on the image side of the prism.

11. A zoom lens system as claimed in claim 8 ,

wherein the most object-side lens unit includes at least one positive lens element and at least one negative lens element on the image side of the prism.

12. A zoom lens system as claimed in claim 5 ,

wherein the prism is included in a most object-side lens unit, and wherein the most object-side lens unit includes a first lens element located on the object side of the prism and fulfills the following conditional formula:

0.4<| flL/flG|< 1.2

where

flL represents a focal length of the first lens element (flL<0); and

flG represents a focal length of the first lens unit.

13. A zoom lens system as claimed in claim 5 , further comprising:

a light amount adjusting member.

14. A zoom lens system as claimed in claim 13 , wherein:

the light amount adjusting member is an aperture stop or a shutter disposed on an image side of the prism.

15. A digital camera comprising:

an image sensor for converting an optical image of a subject into an electrical signal; and

an image-taking lens system for forming the optical image on the image sensor, the image-taking lens system including a prism configured to bend an optical path approximately 90 degrees,

wherein the prism fulfills the following conditional formula:

Ndp>1.9

where

Ndp represents a refractive index for a d-line of the prism.

16. A digital camera as claimed in claim 15 ,

wherein the image-taking lens system is a variable-focal-length imaging optical system.

17. A digital camera as claimed in claim 15 ,

wherein the image-taking lens system includes at least one negative lens element on an object side of the prism.

18. A digital camera as claimed in claim 15 ,

wherein the image-taking lens system includes an aperture stop or a shutter on an image side of the prism.