CALIBRATION OF LHIRES III
The micrometer adjustment of the LHIRES III spectrograph has been calibrated for the 2400 lines/mm grating using the internal Ne standard and Hg lines from a low energy domestic light bulb to cover the shorter wavelengths.
Also shown on the graph is the width of the camera field for the SC3 'PIPCAM' which has 640x7.4um pixels.
Because the collimator is an achromat, the focus has to be adjusted depending on the wavelength. Instead of adjusting the collimator position, which requires opening the spectrograph, I have added a helical focuser in front of the camera. (See here for details) The setting of the focuser is also included on the graph (Note that the equivalent movement of the collimator would be half this distance)
The effect of focusing errors on the line width FWHM has been measured at 6000A. The spectrograph has a resolution of 19000 at 6000A with a nominal 20um slit width, deteriorating about 10% for focus errors of +- 0.15mm (+- 0.075mm collimator position)
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