Re: [APML] OT: KEF Update Questions

["westergren" <westergren@netzero.net>]

Alan,

I doubt trying to focus well before dark would work for two reasons.

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.  The difficulty with KEF is placing the star
next to the edge and holding your eye in the proper position while slowly
moving the scope to see the star wink out at perfect focus.

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

Regards, Don


> Hi all,
>
> Several people have mentioned having difficulty seeing what they're
> supposed to see. Especially in longer focal length systems like SCTs. I
> know this isn't possible later in the night but, has anyone tried going
> out well before darkness falls and using the KEF then? I do not use a
> KEF currently (I think I'll look into it), I usually try to get out
> once the brightest stars start to show. I found this to be an excellent
> time to set up, focus, etc...  If you use this time to force mirror
> flop, focus, check out equipment issues, even find and locate guide
> stars, it does make things easier later.
>
> Alan


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