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Astro-Tech Coma Corrector in a 12" f/4.9 Scope

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#51 Metalmanstan

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Posted 07 January 2013 - 10:31 PM

I'll have to agree with you csrlice12. It seems like the stuff I have to do will be costly because Ill end up breaking something. The nearest professional shop is Highpoint Scientific, which is about 3 hours from here :-(

#52 cjc

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Posted 08 January 2013 - 03:04 AM

Be reassured, I also found it a pain to get this coma corrector working...

If the coma corrector and extensions are fully sunk into the drawer tube to the shoulder of the supplied visual adaptor then I would only expect focus to move in by 10mm or so. It would be worth checking to see how far the focus has actually moved, by trying to focus on closer objects. This will given some idea of how much adjustment you need and what approach to take.

Good luck!

#53 Mirzam

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Posted 08 January 2013 - 05:57 AM

If you use 1.25" eyepieces consider something like this.

Also, if you need to adjust the Paracorr top to a lower setting in order to reach focus, just do it. The effects on coma correction will not be that major.

JimC

#54 cjc

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Posted 08 January 2013 - 08:42 AM

This is interesting and would work, with the right spacing, as a fixed visual interface for 1.25" eyepieces with the ATCC which will screw directly on to the 48mm filter thread. With a 2" parfocalizing ring, you could set the focuser travel arbitrarily.

#55 Starman1

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Posted 08 January 2013 - 10:51 AM

Be reassured, I also found it a pain to get this coma corrector working...

If the coma corrector and extensions are fully sunk into the drawer tube to the shoulder of the supplied visual adapter then I would only expect focus to move in by 10mm or so. It would be worth checking to see how far the focus has actually moved, by trying to focus on closer objects. This will given some idea of how much adjustment you need and what approach to take.

Good luck!


This sounds like the scope is a SkyWatcher dob. SkyWatcher dobs sold in the US have a focuser which has a drawtube larger in inside diameter than 2" and uses separate adapters for 1.25" or 2" eyepieces.
Unfortunately, the 2" adapter has a 1-15/16" opening in the bottom and while that's fine for 2" eyepieces, 2" accessories longer than eyepiece barrels (barlows, coma correctors) will not insert all the way until they rest on the adapter.

This prevents the accessories from working and requires a significant inward focuser movement. It's a bad design.

If it is a Sky-Watcher (aka Synta) dob, you should sand out the bottom of the 2" adapter so 2" accessories will slide through. The bottom hole doesn't even have to be round as long as 2" accessories pass through. This can easily be done with sandpaper while you're watching TV. This alone would probably allow the coma corrector to reach focus.

#56 Metalmanstan

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Posted 08 January 2013 - 02:18 PM

Alright guys, I solved the problem. I took out the primary mirror and placed felt pads below it to give it a little more push to the secondary. Then I Did Don's suggestion and I shimmed down the adapter to get even a little bit more. After that I could focus in on the mountain miles away and I even did it with a barlow attached to a 10mm to see if I could get even closer. Problem solved. I thank everyone for the suggestions, couldn't of done it with out this awesome community!! :jump:

#57 cjc

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Posted 08 January 2013 - 07:13 PM

Well done! I look forward to your report on the difference it makes.






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