Minimum field of view

Using SharpCap's Polar Alignment feature
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cuivenion
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Joined: Wed Feb 15, 2017 7:37 pm

Minimum field of view

Post by cuivenion » Tue Feb 28, 2017 9:37 pm

Hi, what is the minimum field of view needed for polar alignment to work? Is it different in 2.9 and the beta?

Also I plan on using an Altair reducer with my GPCAM to increase the field of view. Are the aberrations from this likely to mess up the plate solving?

Thanks for your help.

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admin
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Re: Minimum field of view

Post by admin » Tue Feb 28, 2017 10:01 pm

I have had reports of success down to about 0.5 degrees FOV. I would imagine that at that level there are probably areas within the supported 5 degrees of the pole that are very low on stars in the star list that SharpCap includes, so if you got unlucky and hit a faint area then you might not get a solution.

I don't recall any reports either way about whether a focal reducer would work. There are two potential problems - lack of sharpness and vignetting towards the edge might make star detection tricky and any pincushion/barrel distortion may cause problems with the plate solving algorithm. The severity of both would depend rather on what sort of telescope you were reducing I think. I think you are going to have to be the guinea pig on this one :)

cheers,

Robin

cuivenion
Posts: 45
Joined: Wed Feb 15, 2017 7:37 pm

Re: Minimum field of view

Post by cuivenion » Tue Feb 28, 2017 10:18 pm

Thanks I'll give it a go. I can see the reducer being a problem but it's worth a try.

calan
Posts: 36
Joined: Mon Feb 13, 2017 7:37 am

Re: Minimum field of view

Post by calan » Wed Mar 01, 2017 6:04 am

I repeatedly had it working with the ASI224MC mounted on a 6" Newt, with a Mallincam MFR-3 focal reducer screwed directly to the camera. According to Stellarium, that gives a FOV of 21' x 28'. I only saw a couple of curved lines, and never the pole or Polaris... but it still worked.

I now use an ASI120MM on a 60mm finderscope, which obviously gives a lot more FOV... but it worked well even with the previous setup.

cuivenion
Posts: 45
Joined: Wed Feb 15, 2017 7:37 pm

Re: Minimum field of view

Post by cuivenion » Thu Mar 02, 2017 7:34 am

Happy to report that it seemed to work fine. I did four aligns, the second was a minute out from the first the third and fourth pretty much matched. I used the colour gpcam with 0.5 reducer in a Skywatcher 130p.

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