PA and plate-solve with narrow FOV

Using SharpCap's Polar Alignment feature
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Joined: Sun Apr 29, 2018 9:34 am

PA and plate-solve with narrow FOV

Post by mtabbara »

I've rushed ahead and purchased a pro license without carefully considering the FOV requirements.

I think I'm doing things the hard way but for reference, the setup I was hoping to get working was PA/plate-solving with a 102mm F7 refractor and an off-axis cam. FOV is 0.4° x 0.3°so it's far too narrow for what SharpCap is supposed to work with but would there be a way (or consider it a feature request) to run the PA algorithm using downloaded star indices e.g., from AstroTortilla, if they were found to be present?

I could bite the bullet and buy a guide/finder scope but it would mean my off-axis gear would be useless unless I bought a second cam for OAG or pulled the cam off the guidescope and attempted to attach and focus it to the OAG. Neither of those options are especially attractive.
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Re: PA and plate-solve with narrow FOV

Post by admin »


sorry but there is no way to use a plate solver like AstroTortilla for the polar alignment - it just wouldn't be quick enough I'm afraid (the internal plate solver that SharpCap uses for polar alignment is tuned for speed, so it can typically solve in less than 1/10s).

People have had success down to about 0.5 degree FOV with the latest versions of SharpCap, so it's worth trying but I think it may not work. Something you could consider trying is to use a 0.5x focal reducer (you can buy these in 1.25" filter thread fit). Some people have been using these for polar alignment when they would otherwise have too small a FOV.

Hope this info is helpful,

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Re: PA and plate-solve with narrow FOV

Post by Biscotte »

Just a line on the FOV subject. It is an observation - not whining or complaining.

Before buying a guidescope and a guide camera I did a lot of research.
Everything pointed at a guidescope focal length should be around half of the main telescope focal length and not less than a third.

Further research for a Meade LX200GPS alt/az at 2000 mm the main recommendation was to go for the 80 mm ST80 types at 400 mm focal length - f/5. Yes, clearly the community was not hidebound by this old school proclamation.

I disembowelled the piggybank and bought an ST 80 mm type with 400 mm focal length and an Orion Starshoot autoguider.
This gives an FOV of 42' x 32'. (~2/3 deg x ~1/2 deg)
It worked well with PHD until LX200 gave up the ghost and died.

Just found your site in the last two days and SharpCap looks to be what my new polar mount needs. If the cloud ever goes away, I'll report back on this size FOV.

If it is even half as good as it looks, it will save hours of frustration in semi darkness!!
Ta in advance

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