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How do you analyse a Flat??


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What software do you use for stacking?  With Deep Sky Stacker (the one I use for my DSLR imaging) you simply put all the frames into their respective sections and press the start button, DSS does the needful on the default settings.

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Must be me, it still doesn't look even, the right side is significantly lighter than the left - unless that is normal?

If the illumination was identical across the frame then you wouldn't need to do a flat subtraction (except for dust bunnies)! The flat is to compensate for uneven field illumination that happens in virtually all scopes.

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ok I need a website recommendation on how to calibrate my flats then, I already have 30 dark/bias frames ready to go.

Neil.

Hi Neil,

Take the relevant subs and put them in their relevant places in DSS and it will do the job once you press the button. I also find that taking flats for a DSLR size sensor is very tricky so a lot of care has to be taken with the Histogram. If you take the Flats using the Av mode the camera exposure system tries for a 50% gray so your histogram ends up somewhere in the middle of the range, I find that this at times causes problems so you can perhaps try and use the exposure compensation button in your DSLR to bring the histogram to about 1/3~2/5 of the  way from the left. You sould also make sure that whatever material you put on the scope ( T Shirt, Linen  etc )  are stretched tight and are free from creases.

~

A.G

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I use a homemade light box for flats. One potential problem is that slightly uneven illumination in the light box or marks on the front panel of the light box could turn up on my master flat. To avoid this possible problem, I take 40 flats, rotating the light box by 90 degrees every 10 frames. From my understanding, the averaging of the flat 'subs' in DSS should smooth out any irregularities in illumination across the light box. The only circumstance where I guess this wouldn't help would be if the light box itself displayed a degree of vignetting.

Sent from my Nexus 7 using Tapatalk

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