Methods and apparatus for focus control in an imaging system

1. An autofocus apparatus, comprising:

a first temperature-sensitive component having a first physical property;

a second temperature-sensitive component positioned adjacent to the first temperature-sensitive component and having a second physical property;

a temperature sensor adjacent to the first and second temperature-sensitive components and configured to:

measure an ambient temperature around the first and second temperature-sensitive components; and

generate temperature data; and

a computation circuit coupled to the temperature sensor and configured to:

receive the temperature data; and

compute a value of the first physical property based on the measured ambient temperature and a first thermal response;

compute a value of the second physical property based on the measured ambient temperature and a second thermal response; and

compute a shift value using the value of the first physical property and the value of the second physical property.

2. The autofocus apparatus according to claim 1 , wherein the first and second temperature-sensitive components each comprise one of:

a lens, a lens barrel, a driving magnet, a spring, a substrate, a sensing magnet, a position sensor, or an image sensor.

3. The autofocus apparatus according to claim 1 , wherein the first temperature-sensitive component comprises a lens and the second temperature-sensitive component comprises a lens barrel.

4. The autofocus apparatus according to claim 3 , wherein the computation circuit is further configured to compute:

the first thermal response of the lens based on the measured ambient temperature; and

the second thermal response of the lens barrel based on the measured ambient temperature.

5. The autofocus apparatus according to claim 4 , wherein the computation circuit computes:

the first thermal response also based on a first thermal time constant of the lens; and

the second thermal response also based on a second thermal time constant of the lens barrel.

6. The autofocus apparatus according to claim 4 , wherein:

the first physical property comprises an effective focal length of the lens and the second physical property comprises a length of the lens barrel; and

the computation circuit is further configured to compute:

the effective focal length of the lens based on the first thermal response; and

the length of the lens barrel based on the second thermal response.

7. The autofocus apparatus according to claim 6 , wherein the computation circuit computes:

the effective focal length also based on a temperature coefficient of the lens; and

the length also based on a linear expansion coefficient.

8. The autofocus apparatus according to claim 6 , wherein the computation circuit is further configured to compute the shift value based on the computed effective focal length and the computed length.

9. The autofocus apparatus according to claim 1 , wherein the computation circuit utilizes the shift value and a target position to compute a corrected target position.

10. A method for determining a magnitude of position shift of two or more temperature sensitive components, comprising:

measuring an ambient temperature;

computing a first thermal response of a first temperature-sensitive component using the measured ambient temperature;

computing a first characteristic of the first temperature-sensitive component using the computed first thermal response;

computing a second thermal response of a second temperature-sensitive component using the measured ambient temperature;

computing a second characteristic of the second temperature sensitive component using the computed second thermal response; and

computing the magnitude of position shift using the computed first and second characteristics.

11. The method according to claim 10 , wherein the first temperature-sensitive component comprises a lens and the second temperature-sensitive component comprises a lens barrel.

12. The method according to claim 11 , wherein:

the computed first thermal response is also based on a first thermal time constant of the lens; and

the computed second thermal response is also based on a second thermal time constant of the lens barrel.

13. The method according to claim 11 , wherein:

the computed first characteristic is also based on a temperature coefficient of the lens; and

the computed second characteristic is also based on a linear expansion coefficient of the lens barrel.

14. The method according to claim 10 , further comprising: computing a corrected target position based on the magnitude of position shift and a target position.

15. An autofocus apparatus, comprising:

a control circuit configured to generate a drive signal;

a lens module responsive to the drive signal, wherein the lens module comprises a lens coupled to a lens barrel; and

a temperature sensor configured to measure an ambient temperature;

wherein the control circuit is further configured to:

compute a first thermal response of the lens;

compute a second thermal response of the lens barrel;

compute an effective focal length of the lens;

compute a length of the lens barrel; and

compute the drive signal according to the first thermal response, the second thermal response, the effective focal length of the lens, and the length of the lens barrel.

16. The autofocus apparatus according to claim 15 , further comprising a position sensor configured to detect an actual position of the lens module, wherein the correction circuit further utilizes the actual position to compute the corrected target position.

17. The autofocus apparatus according to claim 15 , wherein the drive signal is also computed based on a target position.

18. The autofocus apparatus according to claim 15 , wherein:

the first thermal response is based on the ambient temperature and a thermal time constant of the lens; and

the second thermal response is based on the ambient temperature and a thermal time constant of the lens barrel.

19. The autofocus apparatus according to claim 15 , wherein the effective focal length is computed based on the computed first thermal response and a temperature coefficient of the lens.

20. The autofocus apparatus according to claim 15 , wherein the length is computed based on the second thermal response and a linear expansion coefficient of the lens barrel.