UO Ortho - Eye Relief Question

University optics does not list the eye relief of the Abbe Orthoscopics on their website. I'm thinking of getting a 5mm and was wondering if anyone knows what the eye relief for this eyepiece is rated at.

Also, I read where the eye relief on the Celestron Ultima 5mm is 4mm. Is that possible? Wouldn't that mean you'd have to have you eye about 1/8th of inch away from the eyepiece lens?

Yes, 4mm is right. That's about 1/6th of an inch.

The 5mm Ultrascopic is different from the Ultima, in that it's essentially the 10mm Ultrascopic with a built-in 2x barlow; eye relief is the same as the 10mm (about 7mm, if I recall correctly).

The Ortho may have slightly more eye relief, but not much more, than the 5mm Ultima.

Helix (one of the sponsors on the web page) knows the specs of all the U.O. eyepieces they sell.

As Jim noted, eye relief for the 5mm UO is right around 4mm.

Expect a traditional Abbe orthoscopic design to yield eye relief in the realm of ~80% its inherent focal length, but keep in mind that the actual (realized) eye relief will depend on two other major factors: field stop diameter & eyelens recess. A smaller field stop allows for greater eye relief (at the expense of field). Eyelens recess can "gobble up" valuable eye relief, too -- especially so with short-f.l. eyepieces.

Best wishes.
-Dan