Thermal compensation to adjust camera lens focus
An integrated image sensor and a camera lens apparatus comprising of an image sensor substrate, a camera lens mount, a lens barrel, a lens optical assembly and a collet. The camera lens mount comprises a first material, the lens barrel comprises a second material and the collet comprises a third material, the first, second and third materials change in length with a temperature change according to their respective coefficient of thermal expansion. The lens optical assembly comprises optical elements that cause a change in focal length with a temperature change according to a thermal optical coefficient. The first, second, and third material, the lengths of the camera lens mount, lens barrel, and collet, and the thermal optical coefficient of the lens optical assembly are such that the image plane is approximately stationary relative to the sensor surface in response to the temperature change.
1. An integrated image sensor and a camera lens apparatus comprising:
an image sensor substrate comprising an image sensor on an image plane;
a camera lens mount comprising a first material that expands in length with an increase in temperature according to a first positive coefficient of thermal expansion, the camera lens mount comprising:
a base portion including a lower surface adjacent to the image sensor substrate; and
a tube portion extending from the base portion in a direction of an optical axis substantially perpendicular to the image plane, the tube portion having a channel;
a lens barrel having a first portion extending into the channel of the tube portion, and a second portion outside the channel of the tube portion, the lens barrel comprising a second material that expands in length with the increase in temperature according to a second positive coefficient of thermal expansion;
a lens optical assembly secured by the lens barrel, the lens optical assembly comprising optical characteristics that cause a negative change in focal length with the increase in temperature according to a negative thermal optical coefficient;
a collet connecting the interior surface of the camera lens mount and an exterior surface of the lens barrel, wherein the interior surface of the lens mount, the collet and the exterior surface of the lower portion of the lens barrel are each longitudinally oriented in a direction substantially parallel to the optical axis, the collet to couple the lens barrel to the camera lens mount, the collet comprising a third material that expands in length with the increase in temperature according to a third positive coefficient of thermal expansion;
wherein the first material, second material, third material, lengths of the camera lens mount, lens barrel, and collet, and the thermal optical coefficient of the lens optical assembly are such that the focal plane is maintained in approximate alignment with the image plane in response to the increase in temperature.
2. The integrated image sensor and a camera lens apparatus of claim 1 , wherein a change in length of the collet with the increase in temperature is approximately equal in magnitude to a sum of changes in length of the camera mount, the lens barrel and the effective focal length of the lens optical assembly with the increase in temperature.
3. The integrated image sensor and a camera lens apparatus of claim 1 , wherein a change in length of the collet with the increase in temperature moves the lens optical assembly towards the image sensor.
4. The integrated image sensor and a camera lens apparatus of claim 1 , wherein a change in length of the lens barrel with the increase in temperature moves the lens optical assembly away from the image sensor.
5. The integrated image sensor and a camera lens apparatus of claim 1 , wherein a change in length of the lens mount with the increase in temperature moves the lens optical assembly away from the image sensor.
6. The integrated image sensor and camera lens apparatus of claim 1 , wherein the first positive coefficient of thermal expansion for the camera lens mount is in a range of 5 to 20 parts per million per degree Celsius.
7. The integrated image sensor and camera lens apparatus of claim 1 , wherein the second positive coefficient of thermal expansion for the lens barrel is in a range of 30 to 50 parts per million per degree Celsius.
8. The integrated image sensor and camera lens apparatus of claim 1 , wherein the third positive coefficient of thermal expansion for the collet is approximately 100 parts per million per degree Celsius.
9. The integrated image sensor and camera lens apparatus of claim 1 , wherein the negative thermal optical coefficient of the lens optical assembly is in a range of −10 to −20 parts per million per degree Celsius.
10. A camera comprising:
an image sensor substrate comprising an image sensor on an image plane, the image sensor for capturing images or video;
a camera lens mount comprising a first material that expands in length with an increase in temperature according to a first positive coefficient of thermal expansion, the camera lens mount comprising:
a base portion including a lower surface adjacent to the image sensor substrate; and
a tube portion extending from the base portion in a direction of an optical axis substantially perpendicular to the image plane, the tube portion having a channel;
a lens barrel having a first portion extending into the channel of the tube portion, and a second portion outside the channel of the tube portion, the lens barrel comprising a second material that expands in length with the increase in temperature according to a second positive coefficient of thermal expansion;
a lens optical assembly secured by the lens barrel for directing to the image sensor, the lens optical assembly comprising optical characteristics that cause a negative change in focal length with the increase in temperature according to a negative thermal optical coefficient;
a collet connecting the interior surface of the camera lens mount and an exterior surface of the lens barrel, wherein the interior surface of the lens mount, the collet and the exterior surface of the lower portion of the lens barrel are each longitudinally oriented in a direction substantially parallel to the optical axis, the collet to couple the lens barrel to the camera lens mount, the collet comprising a third material that expands in length with the increase in temperature according to a third positive coefficient of thermal expansion;
wherein the first material, second material, third material, lengths of the camera lens mount, lens barrel, and collet, and the thermal optical coefficient of the lens optical assembly are such that the focal plane is maintained in approximate alignment with the image plane in response to the increase in temperature.
11. The camera of claim 10 , wherein a change in length of the collet with the increase in temperature is approximately equal in magnitude to a sum of changes in length of the camera mount, the lens barrel and the effective focal length of the lens optical assembly with the increase in temperature.
12. The camera of claim 10 , wherein a change in length of the collet with the increase in temperature moves the lens optical assembly towards the image sensor.
13. The camera of claim 10 , wherein a change in length of the lens barrel with the increase in temperature moves the lens optical assembly away from the image sensor.
14. The camera of claim 10 , wherein a change in length of the lens mount with the increase in temperature moves the lens optical assembly away from the image sensor.
15. The camera of claim 10 , wherein the first positive coefficient of thermal expansion for the camera lens mount is in a range of 5 to 20 parts per million per degree Celsius.
16. The camera of claim 10 , wherein the second positive coefficient of thermal expansion for the lens barrel is in a range of 30 to 50 parts per million per degree Celsius.
17. The camera of claim 10 , wherein the third positive coefficient of thermal expansion for the collet is approximately 100 parts per million per degree Celsius.
18. The camera of claim 10 , wherein the negative thermal optical coefficient of the lens optical assembly is in a range of −10 to −20 parts per million per degree Celsius.