Variable focal length imaging system

1. A variable focal length (VFL) imaging system, comprising:

a camera system;

a first high speed variable focal length (VFL) lens;

a second high speed variable focal length (VFL) lens;

a first relay lens comprising a first relay focal length;

a second relay lens comprising a second relay focal length; and

a lens controller, wherein:

the first relay lens and the second relay lens are spaced relative to one another along an optical axis of the VFL imaging system by a distance which is equal to a sum of the first relay focal length and the second relay focal length;

the first high speed VFL lens and the second high speed VFL lens are spaced relative to one another along the optical axis on opposite sides of an intermediate plane which is located at a distance equal to the first relay focal length from the first relay lens; and

the lens controller is configured to provide synchronized periodic modulation of an optical power of the first high speed VFL lens and an optical power of the second high speed VFL lens.

2. The VFL imaging system of claim 1 wherein the first and second high speed VFL lenses are approximately identical.

3. The VFL imaging system of claim 1 , further comprising a filter located at the intermediate plane.

4. The VFL imaging system of claim 3 wherein the filter is a fixed pattern pupil filter.

5. The VFL imaging system of claim 3 wherein the filter is a programmable spatial light modulator.

6. The VFL imaging system of claim 3 wherein:

the filter comprises a deconvolution filter; and

the imaging system is configured to provide an extended depth of focus image.

7. The imaging system of claim 3 wherein the filter is at least one of an amplitude or a phase modifying filter.

8. The imaging system of claim 3 wherein the filter is a polarization filter.

9. The VFL imaging system of claim 3 , further comprising a filter wheel configured to provide selectable filters.

10. The VFL imaging system of claim 1 wherein the first high speed VFL lens and the second high speed VFL lens are tunable acoustic gradient index of refraction (TAG) lenses.

11. The VFL imaging system of claim 10 wherein the first high speed VFL lens and the second high speed VFL lens are driven by a shared signal from the lens controller.

12. The VFL imaging system of claim 1 wherein the lens controller comprises a lens response adjustment configuration operable to adjust a resonant frequency of at least one of the first and second high speed VFL lenses such that their resonant frequencies are approximately the same.

13. The VFL imaging system of claim 12 wherein the lens response adjustment configuration comprises a response actuator arrangement configured to alter the resonant frequency of at least one of the first and second high speed VFL lenses, and the lens response adjustment configuration controls the response actuator arrangement to adjust the resonant frequency of at least one of the first and second high speed VFL lenses, such that their resonant frequencies are approximately the same.

14. The VFL imaging system of claim 13 wherein the response actuator arrangement comprises a heat source operable to alter a temperature of at least one of the first and second high speed VFL lenses in order to alter its resonant frequency.

15. The VFL imaging system of claim 1 wherein the first high speed VFL lens and the second high speed VFL lens are separated by a distance SEP along the optical axis which is at least 5 mm.

16. The VFL imaging system of claim 1 wherein the first relay lens and the second relay lens are separated by a distance RSEP along the optical axis which is at least 135 mm.