Optical Design of OPTICAM-ARG: A Three-Channel High-Time-Resolution Camera for the Jorge Sahade Telescope

TL;DR

This paper details the optical design of OPTICAM-ARG, a three-channel high-time-resolution camera for simultaneous multi-band imaging on the Jorge Sahade Telescope, optimized for minimal aberrations and high sensitivity.

Contribution

It introduces a novel optical design integrating dichroics and focal reducers for multi-band, high-time-resolution imaging with optimized aberration correction and performance assessment.

Findings

Achieves a field of view of 8.4 arcmin x 8.4 arcmin per channel.

Establishes an effective focal length of approximately 9.1 m with a uniform plate scale.

Optical performance validated through ray tracing and energy metrics.

Abstract

We present the optical design of OPTICAM-ARG, a multi-channel instrument for the simultaneous acquisition of images in three spectral bands at the Cassegrain focus of an f/8.5 telescope, covering the 0.35 to 1.00 um wavelength range. The converging beam delivered by the telescope is spectrally separated by two dichroics into three channels, blue, green, and red, each incorporating a dedicated three-lens focal reducer, an interchangeable SDSS filter stage, and an sCMOS detector. The focal reducers establish an effective focal length of approximately 9.1 m, a uniform plate scale of 22.6 arcsec/mm, and a field of view of 8.4 arcmin x 8.4 arcmin per channel, consistent with the typical seeing conditions at the site. Operation of the dichroics in a converging beam introduces off-axis aberrations, which are mitigated through wedge angles applied to their second surface and optimized as part of the global design. Optical performance is assessed through exact ray tracing using RMS spot radii and encircled energy metrics, with EE50 values further expressed in terms of an equivalent FWHM to enable direct comparison with atmospheric seeing and to evaluate sensitivity to manufacturing tolerances.