Baader 1.25x GPC orientation

[dweller25]

Hello,

Hope this is the right place to post this question ?

I have an old 1.25x Baader GPC that has no sticker on the side to tell me if it needs mounting in the MK V binoviewer or the Baader Zeiss Prism housing.

I just took out the lens and did this drawing of the cemented doublet.

How should it be mounted in my setup ?

[globular]

Generally speaking*, the casing can be placed either in the binoviewer or in a diagonal.

Placed in the bino gives lower magnification and gives back less back focus.
Placed in the diagonal gives higher magnification and gives back more back focus.
It's a personal preference / choice (or necessity if you are very short of back focus) - but which ever you choose you have to place the lens within the casing orientated so that the convex surface faces away from the binoviewer.
So if the lens is orientated in the casing as in your picture, the casing should be inserted into the binoviewer.

 

*some GPCs are cemented in their case and can not be re-orientated.

[dweller25]

Thank you 👍

[Stu]

Great advice from @globular 👍

Pretty sure it’s the x2.6 which cannot be reversed so has to go in the diagonal. I have a x1.7 which I put in the binoviewer and the x2.6 goes in the diagonal. If I observe and things are very large and the image is soft, I know I’ve left both in there! 🤪🤪

[bosun21]

Yep convex side always orientated towards the scope.

[dweller25]

Thanks to all for the info.

I prefer the extra magnification from mounting the GPC in the prism so I have reversed the lenses.

Thanks for all the replies

Edited December 7, 2023 by dweller25