Re: [APML] SCT mirror lock

["Bobby Middleton" <bobm@koyote.com>]

Yes I do remember from my Meade days that the 12" was designed differently
so you make a good point. I had the 10" and raising the mirror was a good
practice.
Bobby Middleton

http://www.koyote.com/users/bobm/astro1.htm

----- Original Message -----
From: Glenn Graham <glenng@synopsys.com>

> Bobby, that would depend on whether you have an 8"/10" or the 12" since
the 12"
> has a spring to resist the pull of gravity. Unfortulately, how much it
will
> compensate depends on how vertical the OTA is. For my 12" it actually
> over-compensates throughout the range and I actually get a more stable
focus
> when I turn the knob to lower/pull the mirror down onto the spring.
>
> -Glenn
>
> Bobby Middleton wrote:
>
> > ----- Original Message -----
> > From: Steve Walters <swalters@att.net>
> >
> > >But if I crank the focuser to the far ends of its
> > > travel in both directions a few times, the system shows virtually zero
> > > mirror shift when focusing. This is at 200x. I believe Doc G on MAPUG
> >
> > Mapug did have some good info and Doc G had about as much as anybody. I
> > always focused with the final tweek in a clockwise (I think......it's
been 3
> > years) motion. Whichever the correct direction, the point was to RAISE
the
> > mirror instead of lower it. If one lowered it, it might hang on a glob
of
> > grease and settle during the exposure.
> >
> > > I am not saying this eliminates mirror shift all together. I still use
an
> > > OAG for photography. But I have tried various lockdowns and convinced
> > myself
> > > that they don't do much for the shifting. And, if you forget it's
locked,
> > > you could be in for an expensive repair. It's something else to
remember
> > to
> > > do/undo. At 3 am in 14 deg weather, my IQ drops about 70 points. So I
> > > decided against using these gizmos.
> > > A minority view, no doubt.......YMMV.....
> >
> > I was in the minority too; I didn't use lock-down. I also was concerned
> > about forgetting the bolt was in there and anybody who does much
> > astrophotography knows exactly what you mean by IQ dropping at 3 am.
> > I locked the mirror down a few times. I thought that I pulled the system
out
> > of focus when that screw got tight but I never heard anybody else say
this.
> > Bobby Middleton
> >
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>
>
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