Brandon Ocular Eye Relief
Posted 13 August 2013 - 06:56 AM
I've enjoyed this forum for some time, but just joined.
Posted 13 August 2013 - 03:29 PM
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).
Posted 13 August 2013 - 03:41 PM
My eyepieces are the screw-on, fold-down version--the design Questar was using in 1991.
Posted 13 August 2013 - 06:16 PM