From: "Poul Linnet" 
To: 
Reply-To: "Poul Linnet" 


I have just bought a new Maksutov Cassegrain tubus, 90/1200 mm, NoName,
with an internal flipmirror, design similar to the Meade ETX-90. The
mechanical finish is beautiful but the optical performance is ??.

Startesting on Polaris shows a very sharp outer ring with the ocular outside focus
and a very fusy star picture inside focus position. Comparing to Suiter
this indicates
approx. 1/2 wavelength spherical overcorrection.

* Is this normal in this simple 90 mm F/13.3 Mak/Cas design with approx. 15 cm
distance between
   Mirror and Meniscus and the secondary mirror being just an aluminized spot
on the Corrector?

* Are there any possibilities of correcting this by external means ?

* Has anybody a OSLO LT dataset available for this design ?


Poul Linnet
Copenhagen, Denmark

--- BBBS/NT v4.00 MP