Re: [APML]: focusing

[Steve Bell <sb635@delphi.com>]

Ric L Ecker wrote:
> 
> 
> On the Olympus cameras the prime focus of the telescope is not the same
> as the viewfinder.  The foresure method is the knife-edge because it
> takes any guess work out of focusing.  Wearing glasses, my eyes will
> correct focus problems very quickly, which my not be the correct focus
> for the camera. 

The best thing to do, for an OM1, is get the VariMagnifier. This unit
has a diopter corrector, which you can adjust for your particular eyes.
You rotate a ring on the eyepiece to get the OM1's screen in focus for
your particular eyes.

I removed the pentaprism on my Nikon F2 and slipped in a Peak 8x loupe
to give me a magnified view of its focussing screen. I adjusted the
loupe so that it focused on the screen for my right eye (the one I use
to focus with).

> Its easy to get great focus using wide field scopes and
> using the cameras viewfinder with a magnifier but with higher focal
> lengths focus becomes a problem even with a magnifier.  Knife edge at the
> focal plane of the scope eliminated mistakes that bad eyes or ronchi can
> cause.  The Ronchi's work but the camera eliminates one device from
> messing thing up.............
> 

I find it easier to focus on a screen that to do knife edge focussing in
my usually not-very-good seeing conditions. Then, to me, it's actually
harder to tell when the primary mirror goes gray all over as compared to
when a star makes the smallest, tighest dot on a focussing screen. But
doing screen focussing won't work at all unless the camera has been
calibrated, that is, has it's focussing screen come into focus at the
same time it's film plane is in focus. If you frequently get
out-of-focus shots, I'd have the camera checked out.

-- 
Clear skies,
Steve Bell
email: sb635@delphi.com
Astrophoto page: http://people.delphi.com/sb635