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Flat

Demonperformer

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Demonperformer

Demonperformer

Posted
Posted

This morning was my first real attempt at getting flats. Using canon. I know I've read somewhere about getting the intensity right using a histogram, but I'm not sure where to do that on EOS Utils program. When I was looking at them on the screen while taking them, there seemed to be quite a lot of vignetting and it was showing up quite clearly, but the end result from DSS (attached) looks rather flat (if you will excuse the pun) in comparison.

So does this look reasonable for a flat to you imaging gurus, or do I need to get it a bit more pronounced?

Thanks.

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Psychobilly

Psychobilly

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With DSLR's , Shoot the flats in AV mode or if you prefer use AV mode to get the Exposure time and then shoot them in manual at that exposure... Soemtimes when you shoot in AV mode you might end up with groups of flats at two differnet exposures and DSS will only use one or the other - you can edit the exposure time in DSS...

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daz

daz

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I would have said that was too dark for a flat....

As for the vignetting, that is what the flat will show - along with any dust bunnies - as that is what will be subtracted (or divided, can never remember) from the lights.

Flats should be 30-50% of saturation, so you would adjust the exposure time to achieve this.

I have a flat somewhere on this lappy - I'll go dig it out....

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obscura

obscura

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I finished off last night with a bundle of flats -Av - exposure for all was 1/320s. Home made flat field box. Modded 350D with filter removed and with a 2" UV/IR cut filter. Flats reveal the vigging and bunnies. Due to the filter, there is a pinky cast which of course wasn't there before the mod. I assume this is to be expected? If the flats have that then the subs, darks, bias will also have that cast tho' not apparent.

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obscura

obscura

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Posted

Checking the histogram and I am seeing 80% saturation on my pinky flats. These were taken in Av at 1/320s. As aperture is fixed then surely changing to Tv and shutter speed to say 1/640 would reduce exposure on the flats by half. Thus saturation should reduce by up to that factor. Or am I missing a trick again? I'll have to give it a whirl later.

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Demonperformer

Demonperformer

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Well, thanks to all the advice I received, this morning produced what I think is a slightly better result. Hardly surprising when Av was taking exposure 5x longer than I took 'judging it by eye' yesterday. I obviously need to be more automated to get better results!

Thank you all for your help.

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Starflyer

Starflyer

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They look a lot different to mine too :)

I always take them in manual now as I struggled with too much variation using AV. I shoot what I think will be close and check the histogram with Canon's Zoombrowser | properties. I aim for just past half way and then take 50 to 60 shots.

Here's the histogram and a typical, desaturated flat, do these look about right?

post-13749-133877669342_thumb.jpg

post-13749-133877669347_thumb.jpg

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