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Manual flats


Uranium235
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Firstly, thanks to psycobilly for the help with the A mode problem im having with my D60.

It seems there is no way to disable the "no lens attached" message in A mode (like you can with the D200). So it seems im stuck with Manual mode for taking flats, which is a bit of a shame.

So, the question I have is: What would be the average shutter speed needed if i were using a laptop screen as the lightsource?

Ive tried 1/160, but that wast quite right..... just wondering if there was an average for doing it that way so it will save me a lot of messing about with every other shutter speed....hmmm needs investigation as it might be useful for others with the same limitations.

Thanks in advance :)

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How does the histogram look for the pics? IIRC with a dslr you want to be aiming to get the data spike about a third of the way along, starting at the 0 (left) side.

Does the pattern you see in the pics above correspond to that in your astro pics?

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How does the histogram look for the pics? IIRC with a dslr you want to be aiming to get the data spike about a third of the way along, starting at the 0 (left) side.

Does the pattern you see in the pics above correspond to that in your astro pics?

Heres a pic of the histogram, the spike for the 1s exposure is about 1/3rd of the way up - the darkening corners kinda match what happens with my light subs. Maybe 1/1.3 might be closer to the target.

post-18171-133877423134_thumb.jpg

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Looks about right I'd say. NarrowbandPaul might be able to help you a bit more. On my CCD camera I usually aim for about 30k mean ADU value, but I'm not certain what figures would apply for DSLRs. Is it a 12bit camera?

Most important, do the flats work? use them in conjunction with bias frames. You should lose that vignetting. In the middle there is a bit of a shape that would concern me, rather large for a dust bunny and a strange position for a shadow. Is that mark on the light frames too?

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Looks about right I'd say. NarrowbandPaul might be able to help you a bit more. On my CCD camera I usually aim for about 30k mean ADU value, but I'm not certain what figures would apply for DSLRs. Is it a 12bit camera?

Most important, do the flats work? use them in conjunction with bias frames. You should lose that vignetting. In the middle there is a bit of a shape that would concern me, rather large for a dust bunny and a strange position for a shadow. Is that mark on the light frames too?

Yeah the D60 is 12bit, but im discovering its limitations (only M mode works in which metering is disabled). So its truly going to be a manual experience - worth making notes on.

The test shots I posted were done indoors with no particular focus, so I wont know how it will turn out until tomorrow or the weekend when I try it for real at the next session - after ive done the light, dark and bias subs.

The mark you see is probably because the light source was too bright and it was a reflection from the primary, I have the option to dim the lappy screen to make it less aggressive (it has quite a strong backlight).

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Why not try and do the flats at twilight? Or even at dawn if you stay out all night. I use the white t shirt over the front method, aim at a patch of sky away from the setting or rising sun, and grab them quite quickly.

Good luck with it.

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I might be able to try natural flats at the weekend, but at the moment its already dark by the time I get home. Maybe saturday eve will be a good time as its supposed to be clear @ dusk according to the forecast.

Will post the results as I get them. Happy hunting for the weekend! :)

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