I just read a post by jep about not being able to focus and I think I've got the same problem. Last night I finally finished my first scope, an 8" f6. I can't seem to focus on anything, so I assume that I've incorrectly measured distance from back of tube to focuser. I did find Mars (at least I'm fairly certain that's what I found), which appeared as a large disk... but no detail, except for the crisp outline of my spider superimposed on it. Otherwise, I can't see any stars (or anything else). The sky was clear, lots visible to naked eye. There was a fair amount of wind though. The scope had been in my garage during construction, so I'm sure it was at ambient temperature. Here's my setup:
true focal length: 45.5"
focuser height (made of PVC): 1 3/4" (this is measured without eyepiece, right?)
distance from back of tube to surface of mirror: 1 7/8"
(I had incorrectly measured the focuser height to be 2"-- once installed through inside of tube, it was only 1 3/4".) So I calculated:
45.5-2-5= 37.5"
Tacking on the distance from mirror to back of tube, I arrived at 39 3/8" from back of tube to center of focuser hole.
The focuser is one I saw described on a web page (don't have the URL handy) made of PVC drain pipe and PVC electrical conduit... it only has roughly 3/4" of travel.
So my questions are: 1) does my description above lead you to suspect that I've incorrectly placed the focuser on the tube? and 2) if so, how can I correctly determine where to put it? I must say that this thing *looks* impressive, just wish I could see something.
Thanks!
Mark Vincent