Are eye-relief differences across scope copies induced by EPs only? (1 Viewer)

Everyone,

This question came up as myself and another forum member were discussing ER.

Can the objective contribute at all to a noticed ER difference across two scopes / is it all determined by EPs?

We do come across long eye relief EPs for a given scope type, so I also wonder if they completely rectify ER issues a user might have.

Thanks!
Kumar

With the eyepiece you are viewing a virtual image produced by the objective. For those with normal vision the scope would be focussed so as to place this image in the focal plane of the eyepiece. Rays emanating from various points on the objective image would emerge from the eyepiece as parallel bundles and these bundles cross at the exit pupil.
The distance from the eye lens of the eyepiece to the exit pupil is the eye relief. This is independent of the objective.
One does sometimes read of amateur astronomers using a Barlow lens to increase eye relief. However, the Barlow lens effectively increases the focal length of the objective enabling one to use a longer focal length eyepiece for the same magnification. In general, the longer the focal length of the eyepiece, the longer the eye relief.

John

Hi John, thank you very much for the clear explanation. Appreciate it!

Very interesting reading and maybe it will be helpful when I go to buy my next pair of eye glass frames, along with any new lens adjusting if needed. Thanks guys.