Sharpcap live stack

[Jonathancilia]

Hello, i recently started using sharpcap pro and its an amazing software im getting very good deepsky images with my 6 inch dobsonian goto doing EAA. There is an issue however that on the edges of the picture there are black edges that kind of start 'cancelling' the picture, is this because i am using an alt az mount? Cannot do more than 8/10mins total exposure time because the image will be unusable.

[Menno555]

Hi and welcome

I suspect by your description, that you are not using calibration files.
Just to be sure, could you share the image with the problem?

Menno

[Jonathancilia]

I use darks, i did 2 second exposures and 510 gain 20 frames for darks. Will try tonight if it happens again. But basically black edges start appearing at 2 edges of the screen and start cropping inward.

I suspect i am not doing the alignment well for my synscan.
As after this happens i clear live stack and find that the object drifted across the screen, so it must be a frame alignment issue

[Jonathancilia]

I didnt know that i should set the scope to a home position pointing to north, so i guess its a mistake on my part. Usually i just set the scope level and begin alignment and scope goes a completely different direction, then i press cancel and centre the first aligning star and press begin alignment and then its kind of okay. But it does drift sometimes a bit, sometimes too much

[Menno555]

Pointing to the north is a good start, yes
On the black edges: if it looks like the example below, you need flats calibration besides your dark files.

Menno

flats.jpg (97.05 KiB) Viewed 1142 times

[Jonathancilia]

No it doesnt look like that they are 2 edges that are because the image drifts abit.

[Jonathancilia]

Screenshot_20230215_130543_Chrome.jpg (287.1 KiB) Viewed 1140 times

Not my image but i am getting the same black edges like this one in mine, only thing is they are bigger that make the image unusable

[Jonathancilia]

I will have a go again toinight to see if i can align the scope better. As far as darks what settings are best to use? Yesterday used 510 gain and 2000ms exposures for darks and bodes galaxy was extremely noisy. But cigar galaxy came out fine.

Screenshot_20230214_235733_YouCut - Video Editor.jpg (631.99 KiB) Viewed 1137 times

Screenshot_20230214_234638_Gallery.jpg (286.82 KiB) Viewed 1137 times

[admin]

Hi,

the black margins along the edges are caused by the image being captured gradually shifting (as your telescope is not quite tracking the sky perfectly). The shift is slow, so will not show up much in any individual frame, but builds up over time. SharpCap is correcting for the shift by lining up the stars in each image before stacking, but the shift means that some areas near the edges of the image stop getting new data (since they basically have drifted out of view). Those areas will gradually become darker.

The two approaches you can take to this are trying to get your telescope to track better (more care when setting up and aligning), although this will probably never cure the issue entirely, and anyway with a dob mount the image will slowly rotate two (which is unavoidable). The other option is just to crop the image to remove the black areas.

cheers,

Robin

[Jonathancilia]

Thank you for the reply i will definitely try to make the telescope track better, wouldnt mind having abit of black areas i can just crop them out