Eye pieces can fit both 1.25" and 2" ?

[ThunderStorm]

New to astronomy and noticed how come some eyepieces fit both sizes of focuser?
eg.
http://www.bintel.com.au/Eyepieces-and-Barlows/Orion/Stratus/Orion-Stratus-24mm/301/productview.aspx

[MortonH]

In that example, the bottom of the black part is designed to fit nicely in a 2" focuser. It's just a convenience thing for some people who have big 2" eyepieces and don't want to fiddle with an adapter when they switch from 2" to 1.25" eyepieces. It doesn't change the performance of the eyepiece.

Note that it works fine with a Newt/Dob but if you have a scope with a star diagonal you need to make sure the chrome part of the eyepiece has enough clearance so it doesn't hit the mirror in the diagonal.

[DavidNg]

Has both 1.25" and 2" barrels, like this TV in picture:

http://www.company7.com/televue/graphics/13eth125inch_350370.jpg

[ThunderStorm]

Sorry, I am afraid I don't know what is a star diagonal?

[MortonH]

In refractors, and certain other types of scope where you look through the end of the scope (rather than in the top/side with your Dob) a star diagonal diverts the light at 90° to make it more comfortable for the observer.

One is shown here in the third small picture:

http://www.bintel.com.au/Telescopes/Refractor/Sky-Watcher-Black-Diamond-ED80/984/productview.aspx

Imagine the scope was pointing nearly vertical. You'd need to be lying flat on the ground to see through it without a diagonal!

[MortonH]

The diagonal is also attached to the scope in the main picture.