Applying Dark Frames with SharpPro Live Stacking

Discussion of using SharpCap for Deep Sky Imaging
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sandconp
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Applying Dark Frames with SharpPro Live Stacking

Post by sandconp » Mon Aug 05, 2019 8:44 pm

I captured 10 dark frames when i ended my night imaging and chose to store them in the darks Sharpcap folder. I did not do the auto apply and decided to use the method Pre-Processing method which I don’t know how to do with a image that has already been stacked. I understand when doing Astrophotography, that the dark frames are added during the individual stacking of frames. But using Sharpcap Pro with Live Stacking, I already have a stacked image so how is this done or is it too late to add it before I bring the FITS file into PixInsight?

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Re: Applying Dark Frames with SharpPro Live Stacking

Post by admin » Mon Aug 05, 2019 8:47 pm

Hi,

If you want to use darks when live stacking you need to select the dark frame before you start stacking, which in turn means you need to capture your darks before capturing your light frames. SharpCap will then subtract the dark from each captured light frame and then add the result to the stack.

If you have already captured images without using darks then you may have enabled the option to save the raw frames while live stacking in which case you could reprocess those in another application using your dark frames that you captured later.

Cheers, Robin

sandconp
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Re: Applying Dark Frames with SharpPro Live Stacking

Post by sandconp » Mon Aug 05, 2019 9:03 pm

Robin,

Ok that makes sense I was trying to understand how would apply the darks when the image is already stacked so it’s actually reverse in EAA compared to true Astrophotography. I do understand that I have the option of cutting individual frames and then using a program like Deep Sky Stacker to add the dark frames but that would defeat the purpose of live stacking with Sharpcap.

Since my gain and exposure could vary a bit depending on what I am imaging, I suppose I would need separate dark frames for each image I am working on?

Thanks.

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Re: Applying Dark Frames with SharpPro Live Stacking

Post by admin » Wed Aug 07, 2019 3:13 pm

Hi,

For dark frames to work successfully they basically need to have exactly the same settings for the camera as the light frames – the best thing to do is to get all the camera settings correct, then cover the telescope and take the dark frames and then start capturing light frames.

Cheers, Robin

sandconp
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Re: Applying Dark Frames with SharpPro Live Stacking

Post by sandconp » Wed Aug 07, 2019 6:02 pm

I suppose I could check the option to cut each individual frame and then go back in later to apply the dark frames? Is that called post processing and what are the steps to do that in Sharpcap?

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Re: Applying Dark Frames with SharpPro Live Stacking

Post by admin » Thu Aug 08, 2019 3:15 pm

Hi,

I'm not sure I understand what you mean by 'cut' each frame. You can save each frame that is captured during live stacking by checking the 'save raw frames' checkbox. If you do that then you can reprocess all the frames later in a different application like deep sky stacker and apply whatever dark or flat frames you have in that second processing.

Cheers, Robin

sandconp
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Re: Applying Dark Frames with SharpPro Live Stacking

Post by sandconp » Thu Aug 08, 2019 8:27 pm

Robin,

I meant save raw frames like you stated. Doesn’t that kind of defeat the process of live stacking except for the visual experience on the laptop?

I know that I could apply the dark frames right before I live stack like you had mentioned earlier but that seems kind of backwards because you won’t know what to put in for exposure or gain to create your darks until you find the image and focus on it. I would then have to cap the camera and take the darks and uncap the camera to take the light images of the object I am targeting.

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Re: Applying Dark Frames with SharpPro Live Stacking

Post by admin » Fri Aug 09, 2019 7:39 pm

Hi,

Some people certainly save the raw frames in order to do exactly what you suggest – watch the image appear in real time during the observing session and then reprocess completely later to get the best possible results.

Your suggestion about when to take the dark frames is correct – once you have your gain and exposure set just before starting stacking. Of course with a little experience you may find a set of camera settings that works well for you on a range of targets and make those your defaults – for example 30 seconds at gain 200 – once you have that set of defaults and dark frames captured for them you can simplify your workflow.

Cheers, Robin

sandconp
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Re: Applying Dark Frames with SharpPro Live Stacking

Post by sandconp » Sat Aug 10, 2019 10:49 am

Robin,

Thanks for this information it was very helpful.

So just to confirm. There is no way to add the dark frames to the raw images within Sharpcap after my imaging sessions which means I would need to use a program like Deep Sky Stacker ?

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Re: Applying Dark Frames with SharpPro Live Stacking

Post by admin » Sun Aug 11, 2019 7:08 pm

Well…

SharpCap 3.2 has a tool called the folder monitor camera which works a bit like other cameras, but takes its images from a folder that either already has image files in or that has image files being added to it by another program. In theory you could point the folder monitor camera to your folder full of raw live stack frames and rerun the stack using that camera and dark frame and/or flat frame. If you want to take that approach then you'd probably be best off looking up the folder monitor camera in the SharpCap documentation for starters. Deep sky stacker might actually be easier!

Cheers, Robin

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