Overview

Main instrument: Celestron C9, diameter: 235 mm, focus length: 2350 mm

Guide scope: Celestron C5, diameter: 125 mm, focus length: 1250 mm

Finder scopes: Meade 9 x 60, Celestron 6 x 30

Mount: Losmandy G9, 12V-stepper motors for both axes

Electronics: Speed from 0,2x to 32x, declinations backlash compensation

Special accessories: Celestron Advanced Astro Master, encoders for both axes

Other lenses for photography: 500 mm f/5,6 or f/4, 300 mm f/5, 135 mm f/1,8, 50 mm f/1,7

Rear side of the telescope

The C5 comes with a handle reaching from the mirror cell to the correction plate cell. This handle is meant for mounting accessories. I used it to mount the C5 on an aluminium plate that was bolted to the C9 and reached from the mirror cell to the correction plate cell. This is a very rigid setup but unfortunately the C5 cannot be moved relative to the C9 to acquire a guide star. The additional weight of the C5 riding on the C9 required a heavier counter weight.

For doing astrophotography with a SCT usually an off-axis guider is recommended because with a separate guidescope guiding error caused by differential flexure and mirror and focus shift during the exposure are said to be very likely. When I failed to obtain round stars then it was due to poor manual guiding. The guiding and (probably to some extend) polar alignment errors were certainly bigger than any error introduced by flexure or mirror shift.

The C9 is equipped with a Shapley lens (focal reducer and field flattener) that shortens the focal length to 1480 mm at f/6.3 and introduces some vignetting with a SLR camera.

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