Using a CS lens for polar alignment tool?

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MrAstroBen
Posts: 50
Joined: Fri Mar 16, 2018 12:19 pm

Using a CS lens for polar alignment tool?

Post by MrAstroBen » Mon Mar 04, 2019 11:02 am

I have a couple of Astrotrac mounts and wish to use Sharpcap for polar alignment.

A CS lens fitted to my 290M camera would be the neat solution.

Question is how short a focal length could I get away with before pixel scale could affect the results?

Has anyone tried this?

100mm CS lens would give
5.98" 3.19 x 1.79deg

60mm would give
9.97" 5.32 x 2.99deg

Cheers Rob

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admin
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Re: Using a CS lens for polar alignment tool?

Post by admin » Mon Mar 04, 2019 7:00 pm

Hi,

I have had reports of people succeeding with 50 mm lenses, although I don't know what size sensor they were using. The most likely issue with a large field of view would be that the distortion due to the spherical geometry not being correctly modelled might affect the plate solving algorithm. Even if that's the case, using an ROI to cut down the field of view would probably fix the problem.

100 mm is close to the 130 mm focal length of some of the many guide scopes that are being successfully used, so that one should work fine.

Cheers, Robin

SteveInNZ
Posts: 38
Joined: Tue Feb 14, 2017 6:56 pm

Re: Using a CS lens for polar alignment tool?

Post by SteveInNZ » Mon Mar 04, 2019 8:00 pm

I use a QHY5L (same sensor size) with a 25mm lens which is the same as the Polemaster. Being in the southern hemisphere, we are pointing it into a big dark void so the wide field of view helps a lot. At a dark site, SharpCap solves almost straight away.

Steve.

MrAstroBen
Posts: 50
Joined: Fri Mar 16, 2018 12:19 pm

Re: Using a CS lens for polar alignment tool?

Post by MrAstroBen » Mon Mar 04, 2019 8:18 pm

Thanks. I may try a 60mm then. More compact and can pick those up for little.

Thanks Rob

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