wavelength shift

Robin Leadbeater

OK,   I think the constant shift with just the lamp confirms that there was some shift in the spectrograph (It is very small. I think 3A equates to about 5um or about a pixel).  The changing temperature might have been a factor. With the ALPY I  usually take a lamp spectrum each time I change target  during an observing run even though I normally dont see any shift during the night. (With the LHIRES I  see a lot of movement so I take a lamp spectrum at start and end on every target and every half hour or so during long exposures but it is much less stable thermally and mechanically than the ALPY)