--- In Baader-Planetarium@yahoogroups.com, "Tim" <tim_patton_1999@...>
wrote:
>
> I have an 8mm Baader eyepiece. It says you can use it for 1.25" or 2".
> Do i need to order a 2" barrel
>

I presume that you are talking about the Hyperion 8mm. This eyepiece
has both barrels built in: the 1,25" is the chromed tip and the 2" is
the basis of the black body.

You can use any of both barrels (1,25" or 2") if: 1.- you can get
focus or 2.- the tip of the 1,25" barrel don't touch the mirror of the
star-diagonal in use.

respect point 1.- you can note that there is a difference in position
of the eyepiece if you attach it in a 2" focuser or in a 1,25"
focuser. In a SCT you have a lot of back focus (focus travel) but in a
Newtonian can be compromised and the you could need a 2" extension tube.

You could need an extension tube also if you are using the EP in a
star diagonal.

Patricio