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Watec’s illumination issue

During one observing night in December 2011, I noticed a strange “illumination” in the field, as the image from MetRec shows.

 

What is obvious from the above image is that there is too much light coming from the bottom, which affects the regions of interest, the flat-field image and the sensitivity image. As a consequence this area of the field-of-view is inactive.

Visual inspection of the lens didn’t reveal any dust. Unplugging the camera (Watec 902H2 Ultimate) and restarting MetRec a couple of times didn’t work either. It is possible, since I don’t remember well, that the camera started early enough and as it was looking to the west a lot of light was, possibly, captured by the camera and “insisted” through time, like a memory effect.

When the system started next night the “illumination” effect has left! What has happened? Nothing more than that the camera was off for many hours and the cover of the lens was on. Perhaps the last step was the critical one. Since then the system runs smoothly and I don’t intend to experiment further (but possibly may face it again…).