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Old 15-05-2009, 08:27 AM
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multiweb (Marc)
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Question Imaging through a 90deg Diagonal

Is this a nono or is it ok? I realise it's one more mirror but is there any noticeable degradation in your picture? I'm trying to minimise the overhang at the back of my SCT. I thought a diagonal would keep the whole weight closer to the mirror cell and be easier on the focuser. Whats the consensus out there? Thanks for any tips.
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Old 15-05-2009, 10:33 AM
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I would have thought that if the optical quality of the mirror is good enough there should be no degradation of the image aside from some light loss.
Geoff
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Old 15-05-2009, 01:24 PM
gbeal
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Marc,
I have done it before, with the Zeiss 80mm, and the Zeiss prism, for the same reason. It certainly reduces the overhang.
But given an SCT, and bearing in mind the obvious focal length change, can you not simply attach it is close as you dare, and refocus, doesn't the primary shift enough?
Gary
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Old 15-05-2009, 02:58 PM
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multiweb (Marc)
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Quote:
Originally Posted by gbeal View Post
Marc,
I have done it before, with the Zeiss 80mm, and the Zeiss prism, for the same reason. It certainly reduces the overhang.
But given an SCT, and bearing in mind the obvious focal length change, can you not simply attach it is close as you dare, and refocus, doesn't the primary shift enough?
Gary
I use an off axis guider. There's a fair bit hanging .. even with the focuser racked in.
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Old 16-05-2009, 11:22 AM
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Mmm OAG's change things thats for sure! You should be ok to use a diagonal, lets face it, SBIG's first AO unit, the AO-7 is a diagonal.. so obviously, if it works for them... Technically I wouldnt as it introduces another object that can move or flex during imaging, however if you already have a 2" diagonal, it can not hurt to try can it?
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Old 17-05-2009, 02:34 PM
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multiweb (Marc)
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Thanks Alex. I'll check it out.
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