Comment on 'Color astrophotography with a 100 mm-diameter f/2 polymer flat lens', Appl. Phys. Lett. 126, 051701 (2025)

TL;DR

This paper critically evaluates a specific polymer flat lens used in astrophotography, highlighting its extremely low focusing efficiency and poor resolution compared to diffraction limits, which adversely affect image quality.

Contribution

It provides a detailed critique of the lens's optical performance, emphasizing its limitations in efficiency and resolution for astrophotography applications.

Findings

Focusing efficiency is less than 0.03%.

Angular resolution is an order of magnitude worse than the diffraction limit.

Unfocused radiation causes background fog in images.

Abstract

It is argued that the lens described in the paper commented upon has a focussing efficiency of less than 0.03% and an angular resolution for broadband radiation that is an order of magnitude worse that the diffraction limit. Furthermore incident radiation that is not focussed will lead to background fog in the image plane.