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Thanks John. The reason is mainly resolution. I'd like to have the option of shooting at 2600mm (or 1638 with the focal reducer) for deep shots.

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Resolution matters; of course, but I don't think it supports the choice of an SCT. At the Hyperstar focal length of around 500mm a 4" telescope will deliver all the resolution one can use (camera resolution is only 3 arcseconds/pixel or so) without compromises and with the potential of a much larger FOV (image circle of the Hyperstar is limited). At the longer focal length all of the compromises of an SCT (field curvature, spherical aberration, coma) are brought to the foreground. At 2600mm or so, an 8" classical cassegrain can deliver all the resolution a camera can use (.7 arcseconds or so) - again, without compromises (except for the symmetrical obstruction) and, again, with a much larger image circle.

If you really want a single, dual purpose instrument the CN-212 seems to be a much stronger candidate than a C11/Hyperstar combo for only a little bit more money.

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John C
Urban Observatory
Tele Vue Pronto
A&M/Astreya 76mm F/6 APO
TMB/LOMO 80mm F/7.5 APO
Tak FSQ-106N F/5 APO
Meade 152ED F/9 "APO"
Meade 178ED F/9 "APO"
Meade ETX-125AT
Tak CN-212 8" F/12 classical Cass/ F/4 Newt
Teeter 20" F/3.8 truss Newt w/ServoCat
LXD750, EM-200, CI-700
ST-10XME

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