----- Original Message -----
Sent: Saturday, April 26, 2003 12:48 PM
Subject: Re: [M]:flip mirrors


> Optically, a reducer, even a 3.3, should work with a flip mirror, if you
put
> it _after_ the flip mirror. But mechanically, you'd need an adapter to
> connect the SCT threaded reducer to the back of the flip mirror. And
you'd
> need an extension tube for the EP to reach focus with this configuration.
> -John
Yes, and you have the question of how much back focus is needed. The Optec
reducer, 'only' needs about 150mm back focus, so a small flip mirror could
be added in front, and the back focus required from the scope is still not
too bad. Unfortunately, if the flip mirror is small (a 1.25" unit), this
then introduces more vignetting. Given that a 2" flip mirror normally adds
something like 120 to 140mm back focus distance, the total needed from the
scope becomes rather large. The Meade unit, at it's 'design' distance (about
59mm), needs about 180mm back focus at the compressor. Add a 2" flip mirror
to this, and you need over 300mm back focus at the scopes rear port. This is
beyond the distance available from most scopes, and introduces a lot of
aberration (the aberration on the scope rises as you move further from it's
design focus distance...). The extension tube needed for the eyepiece, is in
the order of 150mm or more long, making the whole combination pretty
impractical.

Best Wishes

> >
> >Hi Terry,
> >
> >I think the cons with flip mirrors outweigh the pros, as you're adding
> >weight,
> >length, flexure, instability, etc. to your imaging train. And while a 6.3
> >reducer will work with one, a 3.3 reducer (which is almost a must with an
> >LX200) will not. If you use high precision pointing with the LX200 and a
> >3.3
> >reducer, you should be able to get your deep sky object on the CCD chip
> >every
> >time. And with the advent of USB, it's easy to use the fast downloads of
> >USB
> >and the CCD software for focusing and centering.
> >
> >Clear skies,
> >Rob Bensko

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