Re: More Sputnik Focus Tips

["Paul A. Lehman" <palehman@xxxxxxxxxxxxx>]

Stephen Puckett wrote:

> If you don't want to wait until night, and are somewhat handy, you
> could build a (auto)collimnator to use as a substitute for a star as a
> target at infinity.  Sam Brown's "All About Telescopes" from Edmund
> Scientific explains how to build one, and about knife edge testing for
> focusing.

A "poorman's" collimnator can be done as follows:
Take some old unexposed film, without the paper backing and
scratch an X into the emulsion. Load it into the camera being
sure that it is tight and on the film plain. Leave the back doors
of the camera open and back light the film. Now, take a 35 mm SLR
that you know has a properly focused lens (I use my 135 mm tele)
and set its lens to infinity. (all lenses wide open) Look through
the SLR, through its lens, into the front of the lens of the test
camera, and you will see the scratched X on the film. Adjust the
focus elements of the test camera until the X is in sharp focus
(which will be the infinity setting). Instead of film you can
pencil an X on some ground glass and place it on the film gate.

I recommend using more then one method to double check your work.

Paul A. Lehman