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Replacing or augmenting a focuser

Started by ddoctor, 09/10/2003 03:09PM
Posted 09/10/2003 03:09PM Opening Post
I just finished restoring an old Cave 10" f/6 newtonian. Works great for visual purposes. My concern is that after the restoration the 'rack and pinion' focusing tube required a short extension in order for it to be able to bring things into focus, and now if I have to add any instrumentation, e.g. CCD etc., we're now about 3-4 inches away from the tube. Is there any way to support the focusing tube so it can handle the extra weight in this postion or would you consider replacing the whole tube so it can bring the focus closer in or both. The optics are perfectly collimated now.

Posted 09/10/2003 08:57PM #1
Sounds like you don't have an original focuser. 4" distance from tube would have been about right for *tall* focusers of the day, especially with the Parks or Telescopics' sky-micro focusers (both were original equipment depending on model/year of mfg). You could place a spacer block between focuser and tube, replace the focuser, or move mirror/cell further back in tube to compensate; this last will require re-collimation of primary, but that's not difficult. I wouldn't replace the tube; it's a Parks fiberglass and much better than anything else. Some long-focus Cave Astrola 10" scopes had an add-on Parks shorty tube at the mirror end to extend the length (as seen in S&T ads), both aluminum end-rings mated. You might contact Parks for such as another alternative if you require the additional tube length. If the mirror is original (will be engraved in script with Thomas Caves' own hand on rear) then you have a fine scope indeed. Ron