Design of a custom wideband camera for MISTRAL imager-spectrograph

TL;DR

This paper presents the design of a custom wideband lens for the MISTRAL imager-spectrograph, achieving high throughput and resolution across 370-1000 nm, suitable for spectroscopy and imaging modes.

Contribution

The paper introduces a novel five-lens, two-asphere design for a wideband camera covering 370-1000 nm with high throughput and adaptable imaging and spectroscopy capabilities.

Findings

Achieved 79-98% throughput in the 400-1000 nm band.

Designed a lens with spectral resolving power up to R590-1675.

Maintained image quality within 10% tolerances.

Abstract

MISTRAL is a visible and near infrared imager and spectrograph working with the $1.93m$ telescope at L'Observatoire de Haute-Provence. The goal of the present project is to design and build one custom lens covering the entire working band 370-1000 nm with an enhanced throughput and resolution. The proposed design has the focal length of 100 mm with f/#=2 and consists of 5 lenses with 2 aspheres. It is capable to work in spectroscopy or direct imaging mode with the spectral resolving power up to R590-1675 or energy concentration of 84% within 1 pixel. The throughput varies from 79 to 98% in the main band of 400-1000 nm with a commercial AR coating and could be yet improved with a custom one. We also demonstrate that with this image quality can be maintained in a <10% margin with practically reachable tolerances.