Two-channel imaging system for the White light Active Region Monitor (WARM) telescope at Kodaikanal Observatory: design, development, and first images

One of the three planned back-end systems for the proposed National Large Solar Telescope (NLST) is the Solar Dynamics Imaging System (SDIS) which is intended to obtain near simultaneous images in multiple wavelengths. As a first step, a prototype system with two channel imaging has been developed and installed at the back-end of the White light Active Region Monitor (WARM) telescope at Kodaikanal Observatory. A two-mirror Coelostat serves as a light feeding system to a refracting objective while an optical breadboard serves as a platform for the back-end instruments. A re-imaging system is used before the prime focus to get two light channels for the observations in two wavelengths. The re-imaging system is designed using ZEMAX and the alignment of the system is done using a laser. Full disk images are obtained using a red filter (674.2nm/10nm) and a G-band filter (430.5nm/0.84nm). Design aspects of the re-imaging system, preliminary observations and image reduction methods are described in this paper.