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The National Astronomical Research Institute of Thailand (NARIT) is currently developing a new kind of focal reducer for the 2.4 m Thai National Telescope (TNT). The objective is to image a circular Field Of View (FOV) of 15 arcminute diameter with an image quality close to the seeing limit over the spectral bands B, V, R and I. This focal reducer comprises one doublet lens L1 located on one robotic rail mounted on the telescope fork and one triplet lens L2 mounted on the instrument cube in front of the camera. First, we remind the specifications and the optical design of the instrument. Second, we present the method used to assemble the lenses inside the barrels. Third, we describe the procedure we have used to integrate the focal reducer on the TNT. We describe the robotic rail on which L1 is mounted and we present the results of the wavefront measurement performed to verify the optical quality of the TNT equipped with L1. We also describe the operations of the installation of L2, the filter wheel and the camera on the telescope. Fourth, we present the preliminary performance of the focal reducer measured on-sky with the TNT. We show that the focal reducer provides a resolution close to 1.5’’ over a FOV equal to 12’x12’ limited by the dimensions of the current filters. We also show that the plate scale is equal to 0.6’’/pixel and is stable over the B, V, R and I bands.
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