Liquid optics in a zoom lens system and imaging apparatus

1. A zoom lens system comprising:

a zoom lens group that is axially movable and that has a negative optical power, the zoom lens group comprising a plurality of optical elements of fixed optical power, the zoom lens group comprising an aspheric surface; and

a variable power rear lens group that is axially stationary and that has an optical power that varies between a first optical power and a second optical power, the variable power lens group positioned on an image side of the zoom lens group, the variable power lens group comprising a plurality of optical elements including a liquid lens cell, the liquid lens cell comprising a first contacting liquid and a second contacting liquid, a contacting optical surface between the first contacting liquid and the second contacting liquid configured to change shape to change an optical power of the variable power lens group,

wherein the zoom lens group and the variable power rear lens group are aligned on a common optical axis and configured to collect radiation emanating from an object side space of the zoom lens system, deliver the radiation to an image side space without forming an intermediate image, and focus an image of an object in the image side space at a plurality of focus positions of the zoom lens system,

wherein the magnitude of the negative optical power of the zoom lens group is greater than the magnitude of the first and second optical powers of the variable power rear lens group,

wherein a percentage change in maximum field angle for each focus position relative to an infinity focus position is between −0.2% and −19.5%.

2. The zoom lens system of claim 1 , further comprising an objective lens group that is axially stationary and that has a positive optical power.

3. The zoom lens system of claim 1 , wherein both the first optical power and the second optical power of the variable power rear lens group are positive.

4. The zoom lens system of claim 1 , wherein the zoom lens system has an f-number that varies between F/2.8 to F/4.0.

5. The zoom lens system of claim 1 , wherein a zoom ratio of the zoom lens system is greater than 2.75×.

6. The zoom lens system of claim 5 , wherein the zoom ratio of the zoom lens system is less than 8.5×.

7. The zoom lens system of claim 1 , wherein the zoom lens system provides a modulation transfer function at a spatial frequency of 90 cycles/mm of at least about 58%.

8. The zoom lens system of claim 7 , wherein the modulation transfer function at a spatial frequency of 90 cycles/mm is about 89%.

9. The zoom lens system of claim 1 , further comprising an adjustable iris that is stationary on the common optical axis, the adjustable iris positioned on the common optical axis between the zoom lens group and the variable power rear lens group.

10. The zoom lens system of claim 9 , wherein the adjustable iris is configured to decrease a diameter with an increase in zoom.

11. The zoom lens system of claim 10 , wherein the diameter of the adjustable iris is at least 4.61 mm and less than 6.71 mm.

12. A method of zooming using a zoom lens system, the method comprising:

moving a zoom lens group that has a negative optical power along an optical axis, the zoom lens group comprising a plurality of optical elements of fixed optical power, the zoom lens group comprising an aspheric surface; and

varying a shape of a contact surface in a variable power rear lens group to vary an optical power of the variable power rear lens group between a first optical power and a second optical power, the variable power lens group being stationary on the optical axis and positioned on an image side of the zoom lens group, the variable power lens group comprising a plurality of optical elements including a liquid lens cell, the liquid lens cell comprising a first contacting liquid and a second contacting liquid, a contacting optical surface between the first contacting liquid and the second contacting liquid having a variable shape,

wherein the zoom lens group and the variable power rear lens group are aligned on the optical axis and configured to collect radiation emanating from an object side space of the zoom lens system, deliver the radiation to an image side space without forming an intermediate image, and focus an object in the image side space at a plurality of focus positions of the zoom lens system,

wherein the magnitude of the negative optical power of the zoom lens group is greater than the magnitude of the first and second optical powers of the variable power rear lens group,

wherein a percentage change in maximum field angle for each focus position relative to an infinity focus position is between −0.2% and -19.5%.

13. The method of claim 12 , wherein an axially stationary positively powered objective lens group is aligned along the optical axis with the zoom lens group and the variable power rear lens group.

14. The method of claim 12 , wherein both the first optical power and the second optical power of the variable power rear lens group are positive.

15. The method of claim 12 , wherein the zoom lens system has an f-number that varies between F/2.8 to F/4.0.

16. The method of claim 12 , wherein a zoom ratio of the zoom lens system is greater than 2.75×.

17. The method of claim 16 , wherein the zoom ratio of the zoom lens system is less than 8.5×.

18. The method of claim 12 , further comprising adjusting a diameter of an adjustable iris that is axially stationary, the adjustable iris positioned on the optical axis between the zoom lens group and the variable power rear lens group.

19. The method of claim 18 , further comprising increasing the diameter of the adjustable iris when a zoom of the zoom lens system decreases.

20. The method of claim 19 , wherein the diameter of the adjustable iris is at least 4.61 mm and less than 6.71 mm.