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Old 13-02-2018, 05:42 PM
Imme (Jon)
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Plate solving - months of issues solved

Freaking platesolving has been doing my head in. I mean there was a period there where I walked away from the observatory for 4 weeks just because I couldn’t get it working.
I was spending more time finding and centering targets than I was recording data.
Photos were up, directories were good, everything was linked, pixel size, sensor size, etc were all in but every time I tried to platesolve it would time out and I’d contemplate the bouncing ability of the computer.

.....until I sat back 20 minutes ago and looked at my 800mm focal length telescope. Yep 800mm, says it there right on the side.......but with the qhy8 camera attached to a coma corrector hanging off the side I needed to put a number of extensions on to reach focus.....almost 100mm.......so who’s the fool....me!!!!!!

800mm focal length PLUS my extensions.......I changed the 800mm to 900mm in the focal length settings box (in APT) and BOOM.....plate solves every image I throw at it in less than 10 seconds.

Why am I posting this you ask......hopefully the next poor sucker who struggles with plate solving like I have for months reads this and saves him or herself a great deal of frustration.

Moral of the story - focal length equals the length of your scope plus any extensions used.....not just the scope length (well it did for me).

Feeling stupid that it was such a simple thing that most of you probably know but as someone new to playesolving it isn’t something I read anywhere or was told through my research.

It’s a good day......

Last edited by Imme; 13-02-2018 at 06:11 PM.
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Old 13-02-2018, 06:39 PM
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jwoody (Jeremy)
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I feel your pain Jon, when something is staring you in the face.
Been there before too.........
Glad you have it sorted

Jeremy
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Old 13-02-2018, 07:07 PM
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Camelopardalis (Dunk)
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Yup, sure can be a pain when it doesn't work

APT (amongst other apps) supports two types of plate solving..."hinted" (using PlateSolve2) and "blind" ... hinted is theoretically quicker since it's given a hint as to where to start pattern searching. Blind means search the whole sky without a clue, and hence takes longer.
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Old 13-02-2018, 07:28 PM
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Merlin66 (Ken)
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Hmmm
Adding optics to the set-up can change the effective focal length....
Reducers and Barlows all have an impact.
Easiest solution is to use a blind solve in Astrometry.net - this will establish the focal length etc.
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Old 13-02-2018, 08:25 PM
Imme (Jon)
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Quote:
Originally Posted by Merlin66 View Post
Hmmm
Adding optics to the set-up can change the effective focal length....
Reducers and Barlows all have an impact.
Easiest solution is to use a blind solve in Astrometry.net - this will establish the focal length etc.
Makes perfect sense now i think of it.....but made no sense before!
Guess i just posted in case someone came across the same issue as me and didnt ask the right questions when trying to get it working

...add it to the collective knowledge pool hahahaha
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Old 13-02-2018, 10:32 PM
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barx1963 (Malcolm)
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Hmmmm.... maybe I am missing something, but the focal length of a scope is determined by the optics, not the tube. Extension's are used so that a camera can reach focus in a setup designed for eyepieces. My guess is the coma corrector is the actual issue.
My system is really only interested in the image scale, if that is correct, focal length is irrelevant.
Good to know it is working, as that is what counts!!!

Malcolm
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