2nd July 2021 Imaging problems, then cloud.

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Friday 2nd 63F, early start, bright without cloud. Cloud moved in at 08.50.

I had been struggling to get an even brightness across the frame. I tried different frame sizes and GPCs. The seeing was steady and beautifully sharp at first. So I captured a few videos.

The problem is obvious. Bright at top right and a large wash of brighter [off-band] at lower left.

I tried placing a thin, fibre, plumbing washer on the etalon rubber ing but it made no useful difference. 

I am using a metal rod in the [open] etalon housing. Normally I can find a position where rotation and tilting help even out the lighting. Not today. 

The large area in the left, lower quadrant should be as detailed as the middle, left upper and lower right of the image. The same problem appears at upper right. 

Here I have reduced the frame size to 800x800 to minimise these sweet spot problems without success.

 

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