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Hybrid diagonals in .965 60mm f15 refractors

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#1 choran

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Posted 22 January 2014 - 01:49 PM

Has anyone had experience using hybrid diagonals (.965 to 1.25) in 60mm long focal length refractors? Is there a simple way to determine in advance whether a particular diagonal will cause problems with lack of in focus when utilizing 1.25 eyepieces in such a scope, and will the problem manifest most when using short vs. long focal length eyepieces, or the reverse? Interested specifically in the case of the Unitron 60. This post is prompted by problems reported in another thread involving a similar sized telescope.

#2 terraclarke

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Posted 22 January 2014 - 01:55 PM

I have an older Orion prism one. Its fully coated and made in Japan; it's around 15 years old. I don't use it too often, but it works great when I do. I haven't seen any significant focus issues with it compared to the 0.965" diagonal. When these arise, I find the issue usually more one of the particular eyepiece design than the diagonal.

#3 Geo31

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Posted 22 January 2014 - 02:13 PM

I just got the one from Agena. Gotta run to a meeting, but I just did a big write up in my Jason 325 thread.

#4 Bomber Bob

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Posted 22 January 2014 - 02:15 PM

I had a Meade (Mizar?) model years ago that worked fine on a Tasco (Towa) 80mm.

#5 choran

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Posted 22 January 2014 - 02:24 PM

Yeah George, I read that, and that's what prompted my question. There is probably a way to predict in advance whether problems will develop due to the increased light path. I don't know it, though.

#6 CharlieB

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Posted 22 January 2014 - 02:26 PM

I have several brands of hybrids and the problems are usually from the eyepieces rather than the diagonal. Sometimes, there just isn't enough in-focus on longer f/l 1.25" eyepieces, particularly on 26mm and beyond. That is also a function of where along your focuser tube that the focal plane lies. With the 2-part drawtubes, I've always plenty of in-focus available, but not always so with the one-part.

#7 AllanDystrup

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Posted 22 January 2014 - 02:36 PM

The Unitrons are designed to work with visual backends like the Unihex prism and the star diagonal -- lots of backfocus when the drawtube and the R&P focuser are retracted.

I've used my 60/900 and 60/700mm Unitrons with other diagonals: 0.965" as well as 1.25" hybrids (Meade, Celestron), simple as well as amici diagonals, and never had a problem with back focus, from 40mm to 4mm eyepieces.

I've used my Unitrons with my Zeiss amici rotating EP revolver too, loaded with Zeiss 0.965 and M44 eyepieces plus assorted 1.25" (Celestron, ATC, TV Nagler & Panoptic, plus other) eyepieces, without problems.

Allan

#8 Chuck Hards

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Posted 22 January 2014 - 02:40 PM

I have several brands of hybrids and the problems are usually from the eyepieces rather than the diagonal.


Agreed. I use a hybrid diagonal, and it only adds a couple of millimeters over a dedicated .965" diagonal. I've never had an issue with insufficient racking movement on my 60mm f/16 Penncrest.

#9 starman876

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Posted 22 January 2014 - 02:49 PM

The drawtube on the Unitron can be racked out as far as from VA to CA. you will never have a problem

#10 choran

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Posted 22 January 2014 - 02:52 PM

Thanks all.

#11 photiost

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Posted 22 January 2014 - 02:55 PM

I know there are some lack of in-focus issues with the "smaller" Tasco refractors like their 60mm model 9TE-5

I have an older 1.25" B&Lomb prism diagonal and using that I can bring most eyepieces to focus.

Edit:
Just to add that I have similar issues with the 77mm Swift model 831 and to solve I use the same diagonal on that scope as well.

#12 choran

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Posted 22 January 2014 - 03:43 PM

Thanks again.






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