Continuous Zoom Freeform Afocal Telescope

Continuous zoom afocal systems offer great flexibility for imaging applications. This work investigates the capability and potential of using freeform optics in continuous zoom reflective systems by designing a four-mirror unobscured afocal system with zoom capabilities. The system was optimized at 2X and 3X zoom ratios with a compensated exit pupil. Freeform profiles were used on each mirror for the aberration correction necessary to facilitate the zoom motion. The minimum volume package was found for both the 2X and 3X zoom freeform designs that achieve diffraction-limited performance with less than 5% RMS pupil shape error and pupil offset error. 3x better RMS wavefront error and 3.5x better exit pupil quality were observed in the freeform design compared to the off-axis conic design with identical specifications.