An off-axis, wide-field, diffraction-limited, reflective Schmidt Telescope

TL;DR

This paper presents an off-axis, wide-field, diffraction-limited reflective Schmidt telescope design that offers significant advantages in infrared astronomy, including unobstructed pupils and large, accessible prime focus, with practical implementation benefits.

Contribution

It introduces a novel off-axis reflective Schmidt design optimized for infrared observations, demonstrating its feasibility and advantages for large telescopes like KDUST.

Findings

Achieves diffraction-limited NIR imaging over 1 degree

Provides near-diffraction-limited imaging out to 2 degrees

Offers a gravity-invariant prime focus suitable for large instrumentation

Abstract

Off-axis telescopes with unobstructed pupils offer great advantages in terms of emissivity, throughput, and diffractionlimited energy concentration. For most telescope designs, implementation of an off-axis configuration imposes enormous penalties in terms of cost, optical difficulty and performance, and for this reason off-axis telescopes are rarely constructed. However, for the reflective Schmidt design, implementation of an off-axis configuration is very straightforward, and involves only a modest optical penalty. Moreover, the reflective Schmidt gets particular benefits, avoiding the obstruction of its large focal plane and support column, and gaining a highly accessible, gravity-invariant prime focus, capable of accommodating very large instrumentation. We present an off-axis f/8 reflective Schmidt design for the proposed 'KDUST' Chinese infrared telescope at Dome A on the Antarctic plateau, which offers simultaneous diffraction-limited NIR imaging over 1 degree, and close to diffraction-limited imaging out to 2 degrees for fibre-fed NIR spectroscopy.