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Diagonal vs. image erector

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#1 dcriner



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Posted 02 August 2013 - 07:57 PM

I have a 3.5 duplex that I want to use for terrestrial viewing, through the axial port. I want the image to be correct, vertically - not necessarily left and right. What is the difference between the Questar mirror diagonal and the Questar image erector for this purpose?

#2 Mike E.

Mike E.


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Posted 03 August 2013 - 01:02 AM

The erector inverts the image to the correct orientation for terestrial views.
Questar lists two models of image erectors.....
1.) A straight through # 19450
2.) A premium 45 degree amici prism # 19451.

#3 Les


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Posted 03 August 2013 - 09:13 AM

Just to be clear:


Both present correct orientation vertically. If that is your only requirement then go with the diagonal because it uses less optical surfaces (one) that can degrade image.

#4 dcriner



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Posted 03 August 2013 - 05:33 PM

Mike & Les - that's very helpful advice, thanks. I'm now leaning toward the 45-deg erecting prism - not because I can't deal with a mirror image, but because the 45 deg will be easier to deal with for terrestrial viewing. For the 90-deg mirror diagonal, I might as well look down into an eyepiece in the usual location on the top of the barrel of the 'scope?

#5 dcriner



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Posted 18 August 2013 - 08:07 PM

I have received the 45-deg erecting prism. It serves my purposes for terrestrial viewing, fine. Of course, since it threads into the axial port, it does not work with the viewfinder or the built-in Barlow. For a viewfinder, use a long-focal-length eyepiece in the top position of the 'scope - which will also work with the built-in viewfinder.

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