Re: Collimation: aiming the secondary

On Mon, 30 May 2005 21:36:58 GMT, Mac <marmac2@xxxxxxxxxxxxxxxxxxxx> wrote:

Hi all,
Yes, this is yet another collimation question, sorry.
All of my research states to simply "turn" the secondary until it looks like
a circle through the focuser. Is there a more accurate way of making this
setting? After a few minutes of looking I'm not sure what looks like a
circle and what doesn't.
By turning the secondary holder on the spider, am I pointing the optical
axis at the center of the eyepiece/focuser or is it simply trying to grab
the entire light cone? What I mean is, will the axis be pointing towards
the eyepiece/focuser even if the secondary is turned a tiny bit away? I'm a
fairly experienced collimator but have always wondered about this.
10" f4.7 newt.
I offset towards primary and away from focuser, point the secondary at
center of primary using laser, then I tend to like the barlowed-laser for
aiming the primary.
Thanks all,
-Mac


When adjusting the diagonal, it is important that your eye be very near
the center of focuser, at the focal plane, when gauging concentricity.
There are various devices for doing this. The sight tube is the most common. However, a 35mm film canister with a hole centered in the bottom
(top ?) is said to be nearly as good. Many reflectors come with an
alignment cap which fits in the focuser, and has a centered hole.

Most scopes are set up for the focal plane to be about half an inch
beyond the top of the focuser, when it is racked all the way in.
I have a website giving collimation instructions:

 < http://www.vvm.com/~piscescs/collimat/NoTools2.html >

But there are other excellent pages.  See Sky & Telescope's website,
or just search.  Other responders will likely offer their own favorites.

Cheers,
Larry G.
.

Relevant Pages

  • Re: Locating secondary mirror on Newtonian
    ... Uncle Bob wrote: ... "racked-in" height of the focuser and allow for additional distance to ... your camera's focal plane (assuming you want to try 35mm ... little farther up the tube will do. ...
    (sci.astro.amateur)
  • Re: webcam focusing problem
    ... it's real easy to check the focal plane position. ... When I get a new scope and have doubts about its focal plane position, ... Then take a white sheet of paper and handhold it in front of the focuser, ... the same position and try to take some terrestrial images during daytime. ...
    (sci.astro.amateur)
  • Re: webcam focusing problem
    ... mirror up the tube a bit so that this can happen. ... A quick check on where the focal plane is is to take a frosted glass or thin ... paper and put across the end of the focuser and try to find the focus. ... Screw to those blocks with the screws going up the ...
    (sci.astro.amateur)