Construction: Catadioptrical reflector
The VMC features a catadioptric "Field Maksutov" type design with two spherical mirrors and a meniscus corrector element behind the secondary mirror passed twice by the light:
The open tube allows shorter cool down times compared to 8" SCTs but makes the scope more sensitive to tube current if not cooled down properly.
Adaption to Losmandy GM-8 with G11 head.
The VMC has a very robust seconday/corrector holder and spider vane and holds collimation very well. Nevertheless I managed to totally screw up collimation when playing with a holographic focussing aid (which didn't work for the VMC by the way...) and the VMC needed a complete recollimation.
The fast primary mirror makes the VMC quite 'nervous' regarding collimation, small movements of the mirros/collimation-screws have huge results.
I tried the "standard
collimation procedure for Rumak kind maksutov cassegrains"
When I was finished I had quite nice airy discs but:
so something went wrong.
It's possble that there's no 100% accuray in aligning the secondary with a Chesire or laser but it should be a perfect way to start: Align the secondary first, then adjust the primary at a star and then do the very last touch-up of secondary and primary at the extra-/intrafocal star image.
The primary mirror holder of the VMC is quite sensitive regarding too
tight fastened adjustment-screws resulting in severe astigmatism. The
same is heard about the VMC's "brother" VC200L using the same