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Old 23-05-2005, 10:21 PM
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[1ponders] (Paul)
Retired, damn no pension

[1ponders] is offline
Join Date: Nov 2004
Location: Obi Obi, Qld
Posts: 18,778
Hi blackpearl. We haven't heard from you for a while. That could be the problem. I'm not a newt user so i can only quote what I've read/heard.
This comes from Michael Covingtons "Astrophotography for the Amateur"
In order for prime focus photography to work, the telescope has to provide adequate back focus...................with Newtonians there may not be enough back focus. The symptom is that you can focus on nearby objects, such as trees, but not on the sky.

To overcome the problem, you can modify a Newtonian telescope by moving the morror mount a few centimeters forward from its original position in the tube. When this is done, it will then be necessary to insert a small extension tube when using eyepieces, to get them out to the new psoition of the image plane; a suitable extension tube can be made of 1 1/4 inch(35 mm ) sink trap plumbing parts, available at any hardware store. It may also be necessary to enlare the diagonal mirror to get full edge of field illumination with low power eyepieces. You can also replace the focusing mount with a special low profile focuser that takes up less space, thus giving more back focus. On the whole, though, it may be more practical to leave the telescope unmodified and use one of the optical configurations that do not require much back focus, such as afocal or positive projection.

End quote.

I'm sure someone else around here will have an alternative solution
clear skies
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