Re: Pointing Model for Unguided Imaging on a C11" EdgeHD (with primary mirror locked)

W Hilmo

It’s worth a try, but there is no guarantee.


I have an EdgeHD 8, and I have to use an OAG.  I tried “locking” the primary mirror.  The clutches on the EdgeHD scopes are not actually locks.  They are two flexible rods that can be locked with the knobs on the back of the scope.  This greatly reduces the primary mirror tilt as the scope moves, but does not completely eliminate it, since the rods are flexible.  Also, the rods don’t to anything to prevent lateral movement of the mirror, relative to the baffle tube


The upshot of all of this, is that at a 0.5 arc seconds per pixel, 5 minute exposures were not usable and 3 minute exposures had very noticeable elongation.  Exposures under 2 minutes were not horrible, but also not really good.  I did experiments with a guide scope, and I did experiments with going unguided (with a model and absolute encoders).  The only thing that gave me acceptable results was an OAG, which completely solved the problem.


Still, I have heard of others that are locking the mirror clutches and getting acceptable results, so there may be some variability between scopes.  As I said, it’s worth a try to see how your specific scope works.




From: <> On Behalf Of Bruce Donzanti
Sent: Friday, April 2, 2021 3:08 AM
Subject: [ap-gto] Pointing Model for Unguided Imaging on a C11" EdgeHD (with primary mirror locked)


I am once again re-thinking if it makes sense to attempt unguided imaging on my C11" EdgeHD where I have now locked down my primary mirror and upgraded to the Optec FastFocus system where focusing is done solely using the secondary mirror.  This should eliminate the major mirror flop/shift issues due to moving the primary mirror.  My scope is on an AP1100 in a permanent observatory but I do not have encoders.  I use a ZWO ASI2600MM Pro camera (APS-C sensor) and usually use the 0.7x focal reducer.  The question is:  Is it even worth the effort to try building a model to go unguided imaging or is a refractor still the way to go?  Guiding works ok but it can be finicky at times.

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