Expert: Paul Wagner - 10/16/2007

Question
I have a "new" (to me) 14.5" truss dob, ostensibly custom made by Antares. While collimating it I noticed that the Rigel Systems laser finder is severely out of alignment. I lined it up best I could, but still not happy. My main question is: to line this thing up, where do I place my eyeball for best accuracy? Also, do you recommend a laser type or optical? I'm not new to astronomy, just telescopes. The guys at the local club say Tel-Rad is best for laser, but we all know people have their own tastes & preferences. Which type, laser or optical, in your opinion, is most easy to line up the primary with a minimum of fiddling? Thank you in advance for your help.

Answer
Hi Tom

There are as many opinions as there are astronomers about finder scopes.  I started out using an optical one, and I have to admit I still find them the easiest.  But I know very good astronomers who feel the opposite--it may even depend on what kinds of objects you are interested in observing! I've used a BB gun sight for one of my scopes--but I always managed to leave the light one, and killed far too many batteries for my taste.  And I have a Telrad on my bench...but not installed one a scope, for what that's worth.

If the laser finder really is completely out of aligment, I would check a couple of things

1.  Make sure you are using astronomical objects to collimate it.  It seems easier to try this during the daytime, but it just won't work.  Something a couple of miles away will still have so much parallax as to be worthless on a scope like this.

2.  It may also be that the mount for the laser finder itself is too far out of alignment for it to work well.  THat's a problem for the manufacturer, and I would refer it to them.  Usually, there is enough play to make it work.

3.  If the mounting isn't too far off, then start with a bright planet ( so that it is easy to find in the scope ) or Polaris ( which doesn't move, making it ideal for this kind of adjustment over time ).  Put the star ( or planet ) directly in the center of the field for the laser finder.  You may move your eye around a bit, but after while, you will get used to what seems right.  Then find it in the telescope field and center it in the eyepiece.  Now go back to the laser finder and adjust it until you have it centered perfectly.  This may take a few minutes (thank you, Polaris!) but when you are done, you should be able to work around the sky without problems.

4. Finally, you may find some kind of flex or movement in the telescope's primary optics,  If this happens, then the field of view will change.  It's not the fault of the finder...and If you have followed step 3, and still notice that the finder keeps getting out of alignment, than that is likey the problem.

Hope that helps.

Paul Wagner