as shown in Figure \[fig:repeatability\]. The plot shows a large RMS scatter of $ \pm $ 4.5 pixels that can be attributed to the lack of position repeatability. It has also been analyzed that the shift is not the same from one order to another within the same spectrum. This intra order shift is estimated as 0.075 pixels. The lack of zero positioning of the grating is also noticed when the grating motor is turned off at the end of an observational run and turned on again for the next day observations. This would result in inconsistencies in the wavelength calibration procedure.

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Vignetting
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The spectrograph suffers from vignetting as the size of the grating and prism is smaller than the beam footprint (after the dispersion from grating) at different wavelengths. We analyzed the vignetting effect in the system across the detector field using Zemax model of the spectrograph that is shown in Figure \[fig:zmx\_model\]. Three Echelle orders, at the top, center, and bottom, are considered for evaluation. In each order, three wavelengths to the left, center and right are chosen. The wavelength selection is done in such a way as to sample the entire detector for vignetting effects. 