The prototype of KASI-Deep Rolling Imaging Fast-optics Telescope (K-DRIFT) pathfinder is a 300 mm confocal off-axis freeform three-mirror system that has been developed for the detection of extended low surface brightness (LSB; below μV = 28 mag arcsec-2) structures. Until now, it is still very difficult to observe the LSB features due to systematic errors introduced by natural and instrumental effects. To overcome these, we apply the confocal off-axis telescope design theory that removed linear astigmatism, and each mirror made of Zerodur is set as a freeform surface to remove the residual aberration. Through the design, we can get high-quality images in a wide field of view and minimize sky background fluctuations. The size of the entrance pupil of the telescope is 300 mm and the focal length is 1200 mm. The field of view of the telescope is ~1° × 1° and the size of the focal plane is 22.5 mm × 22.5 mm. We have measured root mean square wavefront errors of the system after integration of the mirrors, flexures, and housing. At off-axis fields, the maximum root mean square wavefront error before the alignment is 260 nm, and decreased to 115 nm after alignment. Alignment-induced astigmatism and coma were almost eliminated through the process. In this paper, we briefly present the integration and alignment process of the K-DRIFT pathfinder and the current status of the project.
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