Scientific CMOS sensors in Astronomy: IMX455 and IMX411

Abstract

Scientific complementary metal-oxide-semiconductor (CMOS) detectors have developed quickly in recent years thanks to their low cost and high availability. They also have some advantages over charge-coupled devices (CCDs), such as high frame rate or typically lower readout noise. These sensors started to be used in astronomy following the development of the first back-illuminated models. Therefore, it is worth studying their characteristics, advantages, and weaknesses. One of the most widespread CMOS sensors are those from the Sony IMX series, which are included in large astronomical survey projects based on small and fast telescopes because of their low cost, and capability for wide-field and high-cadence surveys. In this paper, we aim to characterize the IMX455M and IMX411M sensors, which are integrated into the QHY600 and QHY411 cameras, respectively, for use in astronomical observations. These are large (36 $\times$ 24 and 54 $\times$ 40 mm) native 16 bit sensors with 3.76 $\mu$m pixels and are sensitive in the optical range. We present the results of the laboratory characterization of both cameras. They showed a very low dark current of 0.011 and 0.007 e$^{-}$ px$^{-1}$ s$^{-1}$ @$-$10 C for the QHY600 and QHY411 cameras, respectively. They also show the presence of warm pixels, $\sim$0.024% in the QHY600 and 0.005% in the QHY411. Warm pixels proved to be stable and linear with exposure time, and are therefore easily corrected using dark frames. Pixels affected by the Salt \& Pepper noise are $\sim$2% of the total and a method to correct for this effect is presented. Both cameras were attached to night telescopes and several on-sky tests were performed to prove their capabilities. On-sky tests demonstrate that these CMOS behave as well as CCDs of similar characteristics and (for example) they can attain photometric accuracies of a few milli-magnitudes.