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Old 10-10-2018, 11:06 AM
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LewisM
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LewisM is offline
 
Join Date: Aug 2012
Location: Somewhere in the cosmos...
Posts: 10,388
A serious discussion on OAG vs gudescope

I have been using a mini-guidescope for many years. I currently use a Takahashi 7x50 finder with the visual back removed and a non-rotating Borg helical focuser installed instead. I use a Lodestar (original version), and I use Baader finder rings as my rings (allows movement, and VERY precise fit so no slopping or looseness in the rings for the screw jacks). I use a Vixen SXP mount.

I get perfectly round stars each and every time, irrespective of sub-length - a testament not only to the impressive precision of the mount, but also shows - in my opinion - no movement in the guidescope arrangement.

I recently bought a mono CCD. I also bought a Starlight Xpress filter wheel, with integral OAG to go with it. First time I used the OAG I got PLENTY of stars without even having to fiddle or move the prism, just a slight focus tweak. Tracking and imaging with it ellicited precisely the same result as the guidescope image - round stars, time after time. Dithered by 7 pixels per shot now, for both the OAG and guidescope.

So, is there any GENUINE benefit to using exclusively OAG if the system as is produces the same results with a guidescope as with an OAG? Is the hold-over of "OAG is better" only relevant in terms of the "ancient" style of using a large guidescope between widely spaced guide rings?

I know guiding at f/5 is easier than f/8 and above, but is there genuinely any benefit to using OAG in a sagless guidescope system?

For now, my filterwheel OAG has a C thread cap on it as I continue using the finder-guider
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