An empirical comparison of primary baffle and vanes for optical astronomical telescope

TL;DR

This study empirically compares primary baffles and vanes in optical astronomical telescopes, finding both effective in stray light suppression with minimal differences in performance under certain conditions.

Contribution

It provides an empirical evaluation of primary baffle and vane configurations using real telescope observations, introducing an independent vane structure for improved cooling and air circulation.

Findings

Both configurations effectively suppress stray light.

Little difference in stray light uniformity when star-moon angle exceeds 20°.

Independent vane structure enhances cooling and air circulation.

Abstract

In optical astronomical telescopes, the primary baffle is a tube-like structure centering in the hole of the primary mirror and the vanes usually locate inside the baffle, improving the suppression of stray light. They are the most common methods of stray light control. To characterize the performance of primary baffle and vanes, an empirical comparison based on astronomical observations has been made with Xinglong 50cm telescope. Considering the convenience of switching, an independent vanes structure is designed, which can also improve the process of the primary mirror cooling and the air circulation. The comparison of two cases: (1) primary baffle plus vanes and (2) vanes alone involves in-dome and on-sky observations. Both the single star and the various off-axis angles of the stray light source observations are presented. The photometrical images are recorded by CCD to analyze the magnitude and the photometric error. The stray light uniformity of the image background derives from the reduction image which utilizes the MATLAB software to remove the stars. The in-dome experiments results reveal the effectiveness of primary baffle and the independent vanes structure. Meanwhile, the on-sky photometric data indicate there are little differences between them. The stray light uniformity has no difference when the angle between the star and the moon is greater than 20 degrees.