Intes MK66

MK66 with finder scope

Technical data:

Construction: Maksutiv-Cassegrain-Rumak catadioptrical reflector
Clear aperture: d=150mm
f=1800mm, f/12
Primary mirror: d=164mm
Secondary mirror incl. baffle: d=53mm
Mirror materials: LK-5 with reflective aluminum coating and SiO2 protection
Tube diameter: 178mm
Tube length: 530mm
Meniscus lens: K-8 glass with multicoated anti-reflection layers
Focus type: Primary mirror shift
Focus travel: 135mm
Min. focus distance: 20m
Central obstruction 35.3% of d
Theoretical resolution (Dawes): 0.78"
Weight: 6.5kg
Finder scope: 7x35

The MK66 features a catadioptric Maksutov-Cassegrain type design with two spherical mirrors and a full aperture meniscus corrector element.

Scheme of Mak-Cass design

MK66 on Losmandy GM-8

This MK66 is a good example that the "startest" method of judging spherical aberration and optical quality by differences between the intra- and extrafocal out of focus patterns can't always be applied to more 'complex optical systems' like a maksutov cassegrain. There's a really informative essay by Roland Christen of Astro Physics about this topic: Star Testing Complex Optical Systems

My MK66 shows quite distinct differences between the intra- and extrafocal patterns which would indicate quite bad spherical aberrations for a newtonian telescope. However the quality of the in-focus image of this little Mak is without doubt.