Posts Made By: Laurent Labourie

Hello,

I would like to share experience with this eyepiece.

I bought a 5mm Monocentric TMB eyepiece (in Paris). While image is very crisp and perfect at the center of field, eyepiece shows a serious astigmatism at the edge of the field and a mild one near half of the field (Sorry to say but exactly as described in Sky and Telescope). In fact only 15° (half of the field) is usable. This eyepiece is not unusable on the moon. Usable on planets if on optical axis (itself not perfectly centered).

Is that normal or a defect ? What is your experience ?

I am using it with F/7 scopes.

Regards, Laurent

HI,

AP (until now), TEC and Zeiss use oil-spaced objective while TMB, TAK use air-spaced. Now, for TEC and probably others, that's not "oil" but a special two components mix sealed between lenses : neutral chemically and probably with silicone. It stays in by capillarity.

Please note "zero risk" does not exist. But risk with "oil" is not higher than risk with "air" : moisture between lenses (experimented with an old Perl scope), slight shift of a lens...

But risks with these well made scopes are very low. With my TEC140, I think the major risk is I fall with the scope in my hands...

Good luck,

Laurent

You may measure exit pupil :

- magnification = aperture/exit pupil...

Good luck, Laurent

An interferometer is a "machine" and there is no subjectivity. It is very accurate.

A Foucault test is not so accurate and you can "measure" (I say measure) only few things like spherical correction, turned edge... However, an experimented optician can "see" (but only see) much more using a Foucault test. Thus, the couple "Foucault test" + " Experimented optician" can reach a very good accuracy.

If you have a Foucault test in hands, it is very important to know from where...

Markus

Is the head compatible with GP-DX/GP type tripod adapter ? I mean : if I have a tripod for GP-DX is it possible to put this head on top ?

Also : what about encoders ?

Thank you, Laurent

For F/5 to F/7 Scopes :
35mm Panoptic
24mm Panoptic
11mm T6 Nagler
5mm Radian
No barlow