The above is the result of testing flux constancy in images taken of the Hohlraum lamp on a given night, through all filters. Since the lamp is constant and the telescope is not moved then, provided that the FW and shutter works, it should be possible to get constant fluxes for each filter. The above shows that this is hardly the case.
In the first five panels (left to right, top to bottom) we see histograms of the fluxes (cts/s) derived by opening images, subtracting the bias, and extracting the total flux as well as the exposure time and filter name from the headers. We see that in no filter is there a prevalent flux – that is, either the lamp altered its brightness or the FW never acquired the requested filter or the shutter was miles off (so that the requested exposure time was nowhere near the one we got). The bottom right plot shows the fluxes plotted in order of acquisition – since we see straight sequences I think the lamp is not the problem – but the shutter and or the FW is.
Near the top we see a special pattern – this is understood when inspecting the list of of filters and fluxes:
We see that when the filter supposedly changes, the flux is all strange given the otherwise regular sequence.
So: never use the last or first image in a sequence from a stack! Whether this has been the case throughout the 1.5 years of data we soon have, is to be revealed by further analysis. For now, let us simply reject all first and last images in all sequences.
A quick look at the NGC6633 images shows the ABSENCE of the above problem:
The filters did NOT act strange when changed. So – more intermittency, but also a lesson: check all sequences of images for the above problem!