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What does a good versus bad flat look like?
Can someone help out by commenting or posting what a good flat looks like (I use a Canon 400d) - in particular how bright (or dim) the corner versus the edges should be.
I image at ISO 800 and took some flats with a white T shirt over the main OTA lens cap just around sunset with the scope pointing high in a patch of blue sky (taking images of duration 1, 2, 4, 6, 8, 10 , 12 and 16 seconds).
How do I tell what an optimal series of flats should look like please! I presumed you want it semi bright in the centre and fading to dull (not dark) at the edged?
Many thanks,
Matt
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