Re: [APML] OT: KEF Update Questions

[Alan Voetsch <critter12952@yahoo.com>]

Hey Don,

--- westergren <westergren@netzero.net> wrote:
> 1. The KEF and Ronchi focusers need a point source (star light) to
> provide a
> fine focus cut-off at perfect focus.  Looking through the KEF or
> Ronchi, you
> are looking for a sudden dimming with slight movement of the scope as
> the
> focused star passes the edge.  You need contrast to see that, so a
> bright star and a dark sky are best.

On the surface that seems to make the most sense. OTOH, I have always
found it far easier to focus before it gets completly dark. Hey, I'm
weird and this might only work for me. :-) I would much rather get
focused whilt it's still twilight. I wonder if others do this
occaisonally, or if it's just me. I sometimes wonder if too much
contrast is a bad thing. It seems to be much easier against a dark blue
sky. I should re-state that I have not used these instruments (KEFs)
and that I may be way off base here.

> 2. Scopes that are subject to mirror flop need to be focused near the
> target, and before the Earth rotates much.  I suppose focusing once
> early in
> the night at a local point in the sky would work if you wanted to
> photograph targets as they go by that point in the sky.

I've found that using the information via Adam Block on forcing mirror
flop, using a mirror lock, re-checking focus when needed, does a lot to
reduce flop issues. Of course that leaves plenty of other mirror issues
to deal with. That's the nature of the beast. :-)

> I usually end up
> shooting targets all over the sky in one night.

I try not to do that anymore. Seeing as my exposures run to 3 hours and
more (f/10), I've found it more efficient to image one object
repeatedly. Saves bundles of time on setup. Once again, I'll thank
Chris Schur for that advice. Helps when it comes to stacking too
(which, I believe was the subject under discussion when that advice was
given).

Alan

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