Some details SPRAT on LT works from 4000 - 8000 Angstroms. This "one-octave" range is the most onecan get before order overlap in a non cross dispersed spectrograph. On the afternoon of 2017 12 17 the 85mm f/1.8 Nikon camera lenson the LT SPRAT spectrograph was swapped for a 50mm f/1.4 lens .Both lenses are used wide open. This was to testwhat spectral range we could get on a smaller SHOC typeEMCCD detector which has 1024 x 13 micron pixels as opposed to the currentSPRAT iDus detector which has 1024 x 26 micron pixels. The length of the SHOK detector would therefore correspond to 512 SPRAT pixels. This meanswe have to use a wider angle lens to capture the same wavelength range spectrum on a smaller physical length (half the size). The current 85mm lens actually on the SPRAT CCD has anunused portion on the left hand side, and it was calculated that the 50mm lens should"just" work. Note this test is independent of the final collimator focal length chosen for the instrument,as the spectral range on the detector is just a function of the grating lines per mm,the camera focal length and the detector length. Using 512 pixels (numbers from the SPRAT detector with the 50mm lens and taking a Xenon arc we found the following Mean dispersion = 7.70 angstroms/channelStart wavelength = 4073.64 angstromsEnd wavelength = 8018.33 angstromsCentral wavelength = 6009.04 angstroms If desired this could be tweaked slightly (e.g. to go from 4000 to 7950 Angstroms) by titling the cameraslightly. So we can get the full wavelength range. So in summary using the Nikon 50mm lens and SHOK type EMCCD camera works optically from the point of viewof the spectrograph wavelength range.