Subtracting darls /flats in live Stacking

Discussions of Electronically Assisted Astronomy using the Live Stacking feature.
Lee Housden
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Subtracting darls /flats in live Stacking

Post by Lee Housden »

So I no how to capture darks /flats and add to the folder but how do you subtract the darks /flats during a live stack
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admin
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Re: Subtracting darls /flats in live Stacking

Post by admin »

Hi,

the docs for selecting a dark are here

https://docs.sharpcap.co.uk/2.9/#!2!Pre-processing

Flats are just the same, but aren't mentioned in the docs as they were added after SharpCap 2.9

cheers,

Robin
Lee Housden
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Re: Subtracting darls /flats in live Stacking

Post by Lee Housden »

Thanks for your reply robin I have read through the document a few times doesn’t say hew you subtract I can’t see or does SharpCap automatically subtract as soon as you have them in the folder or is there a check box you need to tick so subtraction starts on the live stack
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Re: Subtracting darls /flats in live Stacking

Post by admin »

Hi,

you just need to choose your saved dark file (press the browse button on the dark subtract control). Once you have chosen your dark file it will be subtracted from each frame captured from then on (unless you set the subtract dark dropdown back to 'none'). Same approach for flats.

Hope that makes sense now.

Robin
Lee Housden
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Re: Subtracting darls /flats in live Stacking

Post by Lee Housden »

Perfect thank you
Lee Housden
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Re: Subtracting darls /flats in live Stacking

Post by Lee Housden »

How about bias do we use them in a live stack of are they not needed also what is a good exposure time on deep sky lights and a good gain
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Re: Subtracting darls /flats in live Stacking

Post by admin »

Bias is only useful if you want to use darks that are not the same exposure as your light frames. The theory is that you take the bias away from the dark, then scale the difference according to the difference in exposure between lights and darks, then add the bias back on. If your darks and lights have the same exposure time then bias frames do nothing for you in dark subtraction.

Anyway, SharpCap does not do bias frame calculations, so you need to make sure that you have dark frames taken with the same exposure (and other camera settings) as the light frames.

cheers,

Robin
Lee Housden
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Joined: Mon Feb 12, 2018 5:45 pm

Re: Subtracting darls /flats in live Stacking

Post by Lee Housden »

Thank you for your advice appreciated
Danoglide64
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Re: Subtracting darls /flats in live Stacking

Post by Danoglide64 »

I have had the same question kind of, soooooo, I came here looking and found the answer!

Thank you so much,
Danoglide
carlwagle
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Re: Subtracting darls /flats in live Stacking

Post by carlwagle »

I have spent at least 5 hours today reading all I can about hot pixels and subtracting dark frames and I'm not certain I'm ready to set up on this fantastic night and see if I can subtract black frames from my live stacks.

The line from Robin "you just need to choose your saved dark file (press the browse button on the dark subtract control)" leaves me worried since I can't recall ever seeing the "dark subtract control" to press the browse button on. But this night will be spent OUTSIDE looking for it. Carl
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