Quick newbie EP question

Like many I end up buying sight-unseen, and websites are not always informative Can someone briefly brief me on how some EPs like some Nagler's and Meade UWA have both 2 inch and 1 1/4 inch barrels? I assume the 1 and 1/4 inch insert comes out, so you get the full opening of the 2 when using a 2 inch focuser or diagnoal? Any reason to avoid such EPs when you'll be using it on 2 inch equipment exclusively?

Thanks!Bill Travis

If you take the 'insert' out, you change the eyepiece's properties of focal length, correction, etc. Don't worry there is no vignetting of the field caused by the 'small' looking 1.25" barrel within the 2" barrel. Small lenses at the barrel end with big lenses in the middle is a property of this eyepiece design. Dual barrels make it possible to use them in either 2" or 1.25" focusers as-is.

How is simple - they just put a 2" flange around and above the 1.25" barrel.

Why is fascinating. These Ultrawides start with an aggressive negative lens - like a Barlow - as the field lens. This causes the optical path to expand, and so require a much larger second element group to catch all the light. They then use strongly curved, multi-element eye lenses to pull all that light into your eye while maintaining an extraemely wide apparent FOV.

Since the eyepeice body is so wide, they figure it's more convenient for users to have the 1.25/2" capability built in. Plus, you'll find the 2" position requires more out-focus because it sits deeper in the drawtube. In Newtonians, you want the eyepeice as close to the secondary as possible and this lets you get closer.

HAve fun,
Frank