View Full Version here: : 2" Diagonal Question
Hi. I own a Meade 10” LX200R and want to upgrade to a 2” diagonal.
Wondering if someone can please tell me if todays quality mirror diagonals are the equal or better than a quality prism diagonal and what would best suit my scope? From what I have read the answer can depend on your scope design and focal length, visual or imaging usage and even down to personal viewing preference. What is your own personal preference and why? thanks
28-05-2012, 06:54 PM
i use a 2" meade diagonal nicely finished and machined where it joins my electric focuser the barrel fits nicely into it,the 99 % reflectivity is excellent and all images seem to be clear and crisp thou i use televue eyepieces which also help.the 2" eyepieces fit nicely into the diagonal and there grub screws are large and easy to use same as the 1 1/4' adapter they also have brass rings for tention..i have a new 2" quartz diagonal bnib that i havent used and will keep it for a spare just in case some thing breaks.i noticed that the diagonal is a little dusty and could do with a clean but the images are still excellent.i use it in a 14"sct
Everything I read (on the net)tells me that a quality prism diagonal is better for a long focal length sct and yet many sct owners seem quite happy with a good quality mirror. I just can't decide which way to go.
29-05-2012, 08:22 AM
:) Hi , ELPS .
I have an old 2 inch mirror diagonal from the 1980's ( Celestron ) , a no name 2 inch 96% dielectric from the 90's ( not bad ) and 2 , GSO 99% dielectric Quartz from now ( 2012) .
Using all my refractors, I enjoy trying a comparism between these 3 and mate the new Dielectric Quartz diagonals are the way to go :thumbsup:, in all ways the view is better .
The 1/16th wave might have something to do with this , but the brightness, sharpness and colour rendition are all far superior . :D. in the new Dielectric Quartz diagonals .
In my eye they are worth investing in .
Oh yea , the dielectric reflective couting is guarenteed for 25 years , if left alone . Thats way more than any over coated aliminium coating .
Thanks for the info Brian. Yes, I believe most of the latest quality dielectric coated diagonals are very very good but is this still the best choice for a f10 SCT? Aren't many refractors quite fast regards too focal ratio? From what I understand, scopes below around f8 work best with mirror diagonals and scopes above f8 are better off with a good prism diagonal or maybe there is little difference between the two?
29-05-2012, 05:08 PM
:question: I dont think it makes any differance above about f8 ELPS , all using a prisim diagonal will do is add a little length to the light path so you have to make sure your SCT has anough "in" travel on the focuser to compensate for this . :thumbsup:
I would go a nice dielectric myself , to bring out all your scope can deliver .
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