10

Almost done with my 10" dob project, seems like the closer I get the more that goes wrong! Okay here goes, I'm trying to set the correct distance for my primary. When I do a rough site measurement, do I rack my focuser out or in? I tried the middle, while focusing on a wall indoors (it's cold tonight in Chicago) about 80' away. Went outside and can't see anything! I'm very new to this so hope I can get this done. Thank, Jim.

P.S. Just got done ready forum on "How far is infinity?" might be a help but does anyone have a simple solution? I know primary is about an f6 10". Thanks

James, when I used the NEWT program for my 10" F6 it hit the focus point within 1/16th inch and that error could have been my slop in measuring distances. You must know the *exact* FL of your mirror to use the program with any accuracy.

The answer depends on several things.

First off--yes, you need to know your exact focal length.

Secondly, you need to know where your closest focusing eyepiece focuses, and where it sits in the focuser. (Also throw on your Para-corr or whatever other thing would move your focusing position.) When your closest focusing eyepiece (or eyepiece-Barlow-or ParaCorr) is in focus, your focuser should be cranked all the way down except for maybe 1/4 to half an inch.

This is where the focuser needs to be--in my mind.

I keep the quarter to half inch in there because someday I may buy an eyepiece that focuses even shorter. Also, just collimating can move a mirror some (although 1/4 inch is a bit much on a 10 for collimation movement).

If your focuser does not have a lot of travel, you may need to be even more accurate thann all this.

Does this help?

Alex