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Hi Don
Problems of bringing an image to focus in a camera after attaching it to a telescope focuser usually involve what is termed “Back Focus”.
Sufficient “Back Focus” allows you to attach the camera to the focuser, and then wind the focuser in, or out, until the image is in focus on the camera display.
Newtonian reflectors appear to suffer from not enough “Inward Travel”; that is, you cannot wind the focuser sufficiently in to achieve focus before the focuser hits the end stop on its maximum designed inward travel. This seems to be common for Newtonians and some users can get over this by fitting a low profile focuser, which provides the extra inward travel required.
SCT’s however, focus by moving the main mirror so they have an enormous range of focus and most cameras should easily come to focus in an SCT.
If a low profile focuser does not work on a Newtonian, then some people modify the ‘scope by raising the primary mirror up inside the optical tube, so the image is then projected further outside the focuser tube, hopefully allowing the camera to then come to focus.
Cheers
Dennis
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