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Re: Another Offset Question

Posted: Wed Oct 17, 2018 12:50 am
by cuivenion
Nice one looks like I'm on the way then. Hopefully I'll have a clear night tomorrow to test things out.

Re: Another Offset Question

Posted: Wed Oct 17, 2018 12:56 am
by oopfan
Me too! Keeping my fingers crossed that the weather turns out as forecast. I am collecting darks tonight.

Brian

Re: Another Offset Question

Posted: Wed Oct 17, 2018 5:09 am
by turfpit
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 1052 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

Re: Another Offset Question

Posted: Wed Oct 17, 2018 1:41 pm
by cuivenion
Thanks for the info, looking forward to getting out tonight.

Re: Another Offset Question

Posted: Wed Oct 17, 2018 2:03 pm
by turfpit
Good luck! Looking forward to the results.

Dave

Re: Another Offset Question

Posted: Wed Oct 17, 2018 2:33 pm
by AstroDude
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

Re: Another Offset Question

Posted: Wed Oct 17, 2018 2:56 pm
by oopfan
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

Re: Another Offset Question

Posted: Wed Oct 17, 2018 2:59 pm
by oopfan
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

Re: Another Offset Question

Posted: Wed Oct 17, 2018 3:21 pm
by turfpit
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 1032 times
master-dark-FITS.jpg
master-dark-FITS.jpg (57.8 KiB) Viewed 1032 times

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

Dave

Re: Another Offset Question

Posted: Wed Oct 17, 2018 3:52 pm
by oopfan
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