Lens assembly and imaging device

1. A lens assembly comprising:

a lens unit disposed to face an image sensor; and

a lens holder holding the lens unit, the lens holder comprising:

an inner part to which the lens unit is attached;

an outer part that is disposed on an outside of the inner part relative to an optical axis of the lens unit, and provided with a reference surface to which a positional relationship with the image sensor is configured to be fixed;

a linking part linking the inner part and the outer part;

an inner extension and contraction part for extending and contracting in a direction of the optical axis in association with a change in atmospheric temperature, the inner extension and contraction part being provided between an attachment location of the linking part on the inner part and an attachment location of the lens unit; and

an outer extension and contraction part for extending and contracting in the direction of the optical axis in association with the change in atmospheric temperature, the outer extension and contraction part being provided between an attachment location of the linking part on the outer part and the reference surface,

wherein the inner extension and contraction part and the outer extension and contraction part are designed to extend and contract so as to distance the lens unit from the image sensor when a back focus of the lens unit extends due to the change in atmospheric temperature, and to bring the lens unit close to the image sensor when the back focus of the lens unit contracts due to the change in atmospheric temperature, and

a thermal expansion coefficient of the linking part is smaller than a thermal expansion coefficient of the inner extension and contraction part and a thermal expansion coefficient of the outer extension and contraction part.

2. The lens assembly according to claim 1 , wherein the attachment location of the linking part on the inner part is configured to be closer to the image sensor than the attachment location of the linking part on the outer part.

3. The lens assembly according to claim 2 , wherein the attachment location of the linking part on the inner part is provided on an end part of an image sensor side of the inner part, and the attachment location of the linking part on the outer part is provided on an end part of an opposite side of an image sensor side of the outer part.

4. The lens assembly according to claim 1 , wherein below expression (A) is satisfied:

0.5≤{( a 1× L 1− a 2× L 2+ a 3× L 3)×Δ T}/ΔBf≤ 1.5  (A)

where

a1: the thermal expansion coefficient of the outer extension and contraction part

a2: the thermal expansion coefficient of the linking part

a3: the thermal expansion coefficient of the inner extension and contraction part

L1: a distance in the direction of the optical axis from the attachment location of the linking part on the outer part to the reference surface

L2: a distance in the direction of the optical axis from the attachment location of the linking part on the outer part to the attachment location of the linking part on the inner part

L3: a distance in the direction of the optical axis from the attachment location of the linking part on the inner part to the attachment location of the lens unit

ΔT: an amount of the change in atmospheric temperature

ΔBf: a change amount in the back focus per the change in atmospheric temperature.

5. An imaging device, comprising:

the lens assembly of claim 1 ; and

the image sensor disposed facing the lens unit.

6. A lens assembly comprising:

a lens unit disposed to face an image sensor; and

a lens holder holding the lens unit, the lens holder comprising:

an inner part to which the lens unit is attached;

a middle part disposed on an outside of the inner part relative to an optical axis of the lens unit;

an outer part that is disposed on an outside of the middle part relative to the optical axis, and provided with a reference surface to which a positional relationship with the image sensor is configured to be fixed;

a first linking part linking the outer part and the middle part;

a second linking part linking the middle part and the inner part;

an inner extension and contraction part for extending and contracting in a direction of the optical axis in association with a change in atmospheric temperature, the inner extension and contraction part being provided between an attachment location of the second linking part on the inner part and an attachment location of the lens unit;

a middle extension and contraction part for extending and contracting in the direction of the optical axis in association with the change in atmospheric temperature, the middle extension and contraction part being provided between an attachment location of the first linking part on the middle part and an attachment location of the second linking part on the middle part; and

an outer extension and contraction part for extending and contracting in the direction of the optical axis in association with the change in atmospheric temperature, the outer extension and contraction part being provided between an attachment location of the first linking part on the outer part and the reference surface,

wherein the inner extension and contraction part, the middle extension and contraction part, and the outer extension and contraction part are designed to extend and contract so as to distance the lens unit from the image sensor when a back focus of the lens unit extends due to the change in atmospheric temperature, and contract so as to bring the lens unit closer to the image sensor when the back focus of the lens unit contracts due to the change in atmospheric temperature.

7. The lens assembly according to claim 6 , wherein the attachment location of the second linking part on the inner part is configured to be closer to the image sensor than the attachment location of the second linking part on the middle part, and

the attachment location of the first linking part on the middle part is configured to be closer to the image sensor than the attachment location of the first linking part on the outer part.

8. The lens assembly according to claim 7 , wherein

the attachment location of the second linking part on the inner part is disposed on an end part of an image sensor side of the inner part,

the attachment location of the second linking part on the middle part is disposed on an end part of an opposite side of an image sensor side of the middle part,

the attachment location of the first linking part on the middle part is disposed on the end part of the image sensor side of the middle part, and

the attachment location of the first linking part on the outer part is disposed on an end part of an opposite side of an image sensor side of the outer part.

9. The lens assembly according to claim 6 , wherein

thermal expansion coefficients of the first and second linking parts are smaller than thermal expansion coefficients of the inner extension and contraction part, the middle extension and contraction part, and the outer extension and contraction part.

10. The lens assembly according to claim 6 , wherein below expression (B) is satisfied:

0.5≤{( a 1× L 1− a 2× L 2+ a 3× L 3− a 4× L 4+ a 5× L 5)×Δ T}/ΔBf≤ 1.5  (B)

where

α1: thermal expansion coefficient of the outer extension and contraction part

α2: thermal expansion coefficient of the first linking part

α3: thermal expansion coefficient of the middle extension and contraction part

α4: thermal expansion coefficient of the second linking part

α5: thermal expansion coefficient of the inner extension and contraction part

L1: a distance in the direction of the optical axis from the attachment location of the first linking part on the outer part to the reference surface

L2: a distance in the direction of the optical axis from the attachment location of the first linking part on the outer part to the attachment location of the first linking part on the middle part

L3: a distance in the direction of the optical axis from the attachment location of the first linking part on the middle part to the attachment location of the second linking part on the middle part

L4: a distance in the direction of the optical axis from the attachment location of the second linking part on the middle part to the attachment location of the second linking part on the inner part

L5: a distance in the direction of the optical axis from the attachment location of the second linking part on the inner part to the attachment location of the lens unit

ΔT: an amount of the change in atmospheric temperature

ΔBf: a change amount in the back focus per the change in atmospheric temperature.

11. A lens assembly comprising:

a lens unit disposed to face an image sensor; and

a lens holder holding the lens unit, the lens holder comprising:

an inner part to which the lens unit is attached;

a plurality of middle parts disposed in order from an inside to an outside relative to an optical axis of the lens unit;

an outer part that is disposed outside of the plurality of middle parts relative to the optical axis, and provided with a reference surface to which a positional relationship with the image sensor is configured to be fixed;

a first linking part linking an outermost middle part and the outer part;

a second linking part linking an innermost middle part and the inner part;

a third linking part linking middle parts adjacent to each other;

an inner extension and contraction part for extending and contracting in the direction of the optical axis in association with a change in atmospheric temperature, the inner extension and contract part being provided between an attachment location of the second linking part on the inner part and an attachment location of the lens unit;

a middle extension and contraction part for extending and contracting in the direction of the optical axis in association with the change in atmospheric temperature, the middle extension and contraction part being provided between an attachment location of the first linking part on the outermost middle part and an attachment location of the third linking part on the outermost middle part, and between an attachment location of the second linking part on the innermost middle part and an attachment location of the third linking part on the innermost middle part;

an outer extension and contraction part for extending and contracting in the direction of the optical axis in association with the change in atmospheric temperature, the outer extension and contraction part being disposed between an attachment location of the first linking part on the outer part and the reference surface,

wherein the inner extension and contraction part, the middle extension and contraction part, and the outer extension and contraction part are designed to extend and contract so as to distance the lens unit from the image sensor when a back focus of the lens unit extends due to the change in atmospheric temperature, and to bring the lens unit close to the image sensor when the back focus of the lens unit contracts due to the change in atmospheric temperature.

12. The lens assembly according to claim 11 , wherein

the lens holder comprises three or more of the middle parts and a plurality of the third linking parts, and

the middle extension and contraction part is additionally provided between attachment locations of the third linking parts on the middle parts and attachment locations of other third linking parts on the middle parts.