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Brandon Ocular Eye Relief

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#1 Mike71


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Posted 13 August 2013 - 06:56 AM

First time post. I have a 3.5 Q which I bought new at New Hope in 1991. Superb instrument. Love it! Just returned from its 10-year standard maintenance. Curious, does anyone have information on the eye relief of the Brandon oculars? I have the 24, 16, and 8mm eyepieces.

I've enjoyed this forum for some time, but just joined.

#2 JimK



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Posted 13 August 2013 - 03:29 PM

WELCOME to Cloudy Nights!!!

In general, Brandon ER is 0.8x the focal length, from the glass surface.

There are different models of Brandon eyepieces -- flat-top, volcano-top, screw-off fold-down rubber eyeguard, and probably some others that I am missing.

I have 24mm, 16mm, and 12mm versions with the screw-off fold-down rubber eyeguard. At one point I tried to measure the ER and came up with 9mm, 7mm, and 4mm, respectively, from the flat surface of the eyepiece (*not* the glass), because that was the usable ER for me (and some glass eyepiece surfaces are recessed). The Astronomics website (click here) shows a couple different types of Brandons and when you click on an eyepiece, then select the tech details tab, you can see what Astronomics identifies as the eye relief (for the 8mm screw-top fold-down, they call the ER as 1mm, for the 24mm, they call the ER as 9mm).

#3 Mike71


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Posted 13 August 2013 - 03:41 PM

Thanks, Jim. I suspected numbers like that. I know my cheek has to be up against my 8mm eyepiece to enjoy the full field of view.

My eyepieces are the screw-on, fold-down version--the design Questar was using in 1991.

#4 starboy1954



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Posted 13 August 2013 - 06:16 PM

I have a Tristand which is great but I sit pretty low to the ground to use it. I'm thinking about getting the Astropier as I can stand to view. For those of you who use the Astropier, with an adjustable observer's chair, is it still possible to sit while viewing?

Thanks, Bob

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