A focal reducer is developed for CQUEAN (Camera for QUasars in EArly uNiverse), which is a CCD imaging system on the 2.1 m Otto Struve telescope at the McDonald observatory. It allows CQUEAN to secure a wider field of view by reducing the effective focal length by a factor of three. The optical point spread function without seeing effects is designed to be within one pixel (0.28300) over the field of view of 4.82' × 4.82' in optimum wavelength ranges of 0.8 − 1.1 μm. In this paper, we describe and discuss the characteristics of optical design, the lens and barrel fabrications and the alignment processes. The observation results show that the image quality of the focal reducer confirms the expectations from the design.

ABSTRACT
1. INTRODUCTION
2. OPTICAL DESIGN
    2.1 Design Requirements
    2.2 Optical Layout
    2.3 Optical Performance
    2.4 Sensitivity Analysis and Alignment Tolerance
3. LENS BARREL
4. ASSEMBLY AND ALIGNMENT
5. PERFORMANCE TEST

• JUHEE LIM(School of Space Research, Kyung Hee University)
• SEUNGHYUK CHANG(Samsung Electronics Co., Ltd.)
• SOOJONG PAK(School of Space Research, Kyung Hee University) Corresponding Author
• YOUNGJU KIM(Yunam Optics Inc.)
• WON-KEE PARK(Korea Astronomy and Space Science Institute, CEOU/Departmet of Physics and Astronomy, Seoul National University)
• MYUNGSHIN IM(CEOU/Departmet of Physics and Astronomy, Seoul National University)