Another Offset Question

Discussion of using SharpCap for Deep Sky Imaging
cuivenion
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Re: Another Offset Question

Post by cuivenion » Wed Oct 17, 2018 12:50 am

Nice one looks like I'm on the way then. Hopefully I'll have a clear night tomorrow to test things out.

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oopfan
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Re: Another Offset Question

Post by oopfan » Wed Oct 17, 2018 12:56 am

Me too! Keeping my fingers crossed that the weather turns out as forecast. I am collecting darks tonight.

Brian

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turfpit
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Re: Another Offset Question

Post by turfpit » Wed Oct 17, 2018 5:09 am

Cuivenion

When you next image try this:
  • in SharpCap, set histogram to log view
  • screen capture histogram at offset=0
  • screen capture histogram at offset=whatever the centralised bias frame has told you
  • post pictures of both histograms here
A really good test would be to post final images from using both offset settings - the final proof.

A picture like this is expected (this is an M31 capture and that is quite a bright object)
in-progress-capture2.JPG
in-progress-capture2.JPG (57 KiB) Viewed 904 times
For deep sky, nothing is really visibly in the display but the shape of the histogram tells me all is good.

Now is a good time for you to read https://docs.sharpcap.co.uk/3.2/#The%20Histogram (a shameless plug).

This is what happened to my imaging as I started to understand the histogram viewtopic.php?f=16&t=596. It wasn't an overnight thing and I did have some 'telescope for sale only used twice ' moments.

Find my latest M42 in here viewtopic.php?f=16&t=1199. I can go to the scope and repeat this reliably now, night after night - it only took me 2 years to get there!

I am about to commence writing a book which will cover this topic and others. The secondary title is something like "the book I wish I had when I started out astro-imaging" and this forum thread convinces me it is a worthwhile project.

Dave

cuivenion
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Re: Another Offset Question

Post by cuivenion » Wed Oct 17, 2018 1:41 pm

Thanks for the info, looking forward to getting out tonight.

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turfpit
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Re: Another Offset Question

Post by turfpit » Wed Oct 17, 2018 2:03 pm

Good luck! Looking forward to the results.

Dave

AstroDude
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Re: Another Offset Question

Post by AstroDude » Wed Oct 17, 2018 2:33 pm

Hi, Brian ...
last night after shooting ic1848 in sgp 180 sec gain 1000 offset 50... it clouded over so i started my darks , changing nothing.
the first frame came out with 54 ADU and a Max of 4094.. so im like what the !!
so i went outside tarped up the whole image train and did another 1 ..... same thing...
so to me i though , hey it has to be that big bright star burst on the side of the Sony BSI chip ..

so now what, darks are not darks unless they are \dark !!! or im wrong again..

see pic
Attachments
darks.jpg
darks.jpg (124.73 KiB) Viewed 886 times
Last edited by AstroDude on Wed Oct 17, 2018 3:37 pm, edited 1 time in total.

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oopfan
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Re: Another Offset Question

Post by oopfan » Wed Oct 17, 2018 2:56 pm

Mitch,
the first frame came out with 54 ADU and a Max of 4094.. so im like what the !!
Danger, Will Robinson!

Please inspect your SharpCap Settings dialog, General tab. There is an option to "Save 10/12/14 bit images in FITS files without stretching to 16 bit (Altair, QHY, ZWO cameras only.)"

Seeing that you have an Altair camera, I bet you have that option checked. Right? If you do then that is the reason why DSS is failing to find enough alignment stars!

Brian

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oopfan
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Re: Another Offset Question

Post by oopfan » Wed Oct 17, 2018 2:59 pm

Mitch,
so to me i though , hey it has to be that big bright star burst on the side of the Sony BSI chip ..
You do know that is Amp Glow and not a bursting star? :D That is also why you see it on your dark frames.

Brian

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turfpit
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Re: Another Offset Question

Post by turfpit » Wed Oct 17, 2018 3:21 pm

Mitch

183C master dark, gain=200, offset=150, 180s exposure. Looks as expected.
stretched-master-dark-183C.jpg
stretched-master-dark-183C.jpg (43.79 KiB) Viewed 884 times
master-dark-FITS.jpg
master-dark-FITS.jpg (57.8 KiB) Viewed 884 times

BTW, if you capture in SGP using an Altair 183M, what relevance has that to a SharpCap Forum?

Dave

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oopfan
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Re: Another Offset Question

Post by oopfan » Wed Oct 17, 2018 3:52 pm

Dave,

Thanks for pointing out that he used SGP. I have zero experience with it. I thought he was capturing in SC but used PixInsight to analyze the frames and take screenshots. I saw "SGP" but figured he was using it for guiding.

Sorry Mitch I can't help you any further.

Brian

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