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Old 15-07-2019, 03:53 PM
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bojan
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Join Date: Jul 2006
Location: Mt Waverley, VIC
Posts: 5,884
I have one of those..
http://www.iceinspace.com.au/forum/s...ghlight=opteka

My specimen has a problem with coma.. I think it should be fixable, but I haven't found time for experimenting with moving elements to and fro..
https://www.cloudynights.com/topic/4...ens/?p=7942081

I was talking with couple of other owners (from Astrobin) and it seems my specimen is unique in that respect (that is what gives me hope I will be able to fix it someday).
https://www.astrobin.com/search/?q=500mm+f%2F6.3


Some reviews on web mention focus problem... it is not easy to focus this lens but there is a way around, see last post in the first link.
To make focusing even more precise, I added eccentric cylinder as focus stop. This arrangement with springs not only removes backlash, but with eccentric cylinder (acting as mechanical reductor) it compensates for way too steep focus thread of this lens.


All in all, when (if...) I remove the coma problem, it will be useful as it is very light. and if not, I will use it for guiding.
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Last edited by bojan; 16-07-2019 at 11:16 AM.
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