Image-taking apparatus, and camera and camera system incorporating it
An image-taking apparatus has an image sensor for converting an optical image into an electrical signal, and a taking lens system for forming the optical image on the light-receiving surface of the image sensor. The most object-side surface of the taking lens system is an aspherical surface that has a positive optical power in a central portion thereof and a negative optical power in a peripheral portion thereof, and the following condition is fulfilled: −90<Da<−20, where Da represents the distortion (%) observed at the maximum half view angle in the diagonal direction of the image sensor.
1. An image-taking apparatus comprising:
an image sensor for converting an optical image into an electrical signal; and
a taking lens system for forming the optical image on a light-receiving surface of the image sensor;
wherein a most object-side surface of the taking lens system is an aspherical surface that has a positive optical power in a central portion thereof and a negative optical power in a peripheral portion thereof, and
wherein the following condition is fulfilled:
−90<D a <−20
where
Da represents distortion (%) observed at a maximum half view angle in a diagonal direction of the image sensor.
2. An image-taking apparatus as claimed in claim 1 ,
wherein the following conditions are fulfilled:
0.05 <|f/f asp |<1
0.18 <f /TL<2
0.03<T asp /TL<0.5
where
f asp represents a paraxial focal length of a lens element included in the taking lens system which has the aspherical surface;
f represents a paraxial focal length of the taking lens system as a whole;
TL represents a distance along an optical axis from a vertex of the most object-side surface of the taking lens system to the light-receiving surface of the image sensor; and
T asp represents a thickness along the optical axis of the lens element that has the aspherical surface.
3. An image-taking apparatus as claimed in claim 1 ,
wherein the following condition is fulfilled:
0.2<|ΔZ asp /ΔZ sp|< 5
where
ΔZsp represents amount of spherical sag at a maximum effective aperture; and
ΔZasp represents amount of aspherical sag at the maximum effective aperture.
4. An image-taking apparatus as claimed in claim 1 ,
wherein a most image-side lens element of the taking lens system has a positive optical power.
5. An image-taking apparatus as claimed in claim 1 ,
wherein the taking lens system comprises, from an object side to an image side thereof,
a first lens unit having a negative optical power;
a second lens unit having a positive optical power;
an aperture stop;
a third lens unit having a positive optical power; and
a fourth lens unit.
6. An image-taking apparatus as claimed in claim 5 ,
wherein the lens units are each composed of, at most, two lens elements or one pair of lens elements cemented together.
7. An image-taking apparatus as claimed in claim 1 ,
wherein a most image-side lens element and a most object-side lens element of the taking lens system are each a plastic lens element having an aspherical surface, and
wherein the most object-side lens element of the taking lens system has a negative optical power and the most image-side lens element of the taking lens system has a positive optical power.
8. An image-taking apparatus as claimed in claim 1 ,
wherein the following condition is fulfilled:
2<[21.63 ×f /(0.5×L a )]/[18/tanθv max ]<10
where
La represents a distance from a center to a diagonal corner of the image sensor;
f represents a paraxial focal length of the taking lens system as a whole; and
θv max represents a maximum half view angle in a direction along longer sides of the image sensor.
9. An image-taking apparatus as claimed in claim 1 ,
wherein the following condition is fulfilled:
0<D c /D a< 0.5
where
Dc represents distortion (%) observed on the image sensor at a maximum diagonal angle within a central region of the image.
10. An image-taking apparatus comprising:
an image sensor for converting an optical image into an electrical signal; and
a taking lens system for forming the optical image on a light-receiving surface of the image sensor, the taking lens system comprising, from an object side to an image side thereof:
a front lens unit having a positive optical power as a whole;
an aperture stop; and
a rear lens unit having a positive optical power as a whole,
wherein at least one surface included in the front lens unit is an aspherical surface that has a positive optical power in a central portion thereof and a negative optical power in a peripheral portion thereof, and
wherein the following condition is fulfilled:
−90<D a <−20 where
where
Da represents distortion (%) observed at a maximum half view angle in a diagonal direction of the image sensor.
11. An image-taking apparatus as claimed in claim 10 ,
wherein the following conditions are fulfilled:
0.05 <|f/f asp |<1
0.18 <f /TL<2
0.03<T asp /TL<0.5
where
f asp represents a paraxial focal length of a lens element included in the taking lens system which has the aspherical surface;
f represents a paraxial focal length of the taking lens system as a whole;
TL represents a distance along an optical axis from a vertex of the most object-side surface of the taking lens system to the light-receiving surface of the image sensor; and
T asp represents a thickness along the optical axis of the lens element that has the aspherical surface.
12. An image-taking apparatus as claimed in claim 10 ,
wherein the following condition is fulfilled:
0.2<|ΔZ asp /ΔZ sp |< 5
where
ΔZsp represents amount of spherical sag at a maximum effective aperture; and
ΔZasp represents amount of aspherical sag at the maximum effective aperture.
13. An image-taking apparatus as claimed in claim 10 ,
wherein the following condition is fulfilled:
0 <f f /f r <10
where
f f represents a focal length of the front lens unit as a whole, and
f r represents a focal length of the rear lens unit as a whole.
14. An image-taking apparatus as claimed in claim 10 ,
wherein a most image-side lens element of the taking lens system has a positive optical power.
15. An image-taking apparatus as claimed in claim 10 ,
wherein the front lens unit comprises, from an object side to an image side thereof,
a first lens unit having a negative optical power; and
a second lens unit having a positive optical power, and
wherein the rear lens unit comprises, from an object side to an image side thereof,
a third lens unit having a positive optical power; and
a fourth lens unit.
16. An image-taking apparatus as claimed in claim 15 ,
wherein the lens units are each composed of, at most, two lens elements or one pair of lens elements cemented together.
17. An image-taking apparatus as claimed in claim 10 ,
wherein a most image-side lens element and a most object-side lens element of the taking lens system are each a plastic lens element having an aspherical surface, and
wherein the most object-side lens element of the taking lens system has a negative optical power and the most image-side lens element of the taking lens system has a positive optical power.
18. An image-taking apparatus as claimed in claim 10 ,
wherein the following condition is fulfilled:
2 <[21.63 ×f /(0.5×L a )]/[18/tan θv max ]<10
where
La represents a distance from a center to a diagonal corner of the image sensor;
f represents a paraxial focal length of the taking lens system as a whole; and
θv max represents a maximum half view angle in a direction along longer sides of the image sensor.
19. An image-taking apparatus as claimed in claim 10 ,
wherein the following condition is fulfilled:
0<D c /D a< 0.5
where
Dc represents distortion (%) observed on the image sensor at a maximum diagonal angle within a central region of the image.
20. A camera comprising an image-taking apparatus as claimed in claim 1 or 10 ,
wherein the camera has at least one of a capability of shooting a still picture and a capability of shooting a moving picture.
21. A camera as claimed in claim 20 , further comprising:
a rotating mechanism for rotating the image-taking apparatus at least in one direction to change a shooting direction of the image-taking apparatus.
22. A camera system comprising:
an image-taking apparatus as claimed in claim 1 or 10 , and
an image processor for correcting distortion,
wherein the image processor converts the electrical signal representing the optical image into image data of an image that is roughly similar to a scene perceived by a human eye and that is substantially distortionless.