Re: [APML] SCT mirror lock

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

----- 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



--  APML Archives at <http://astro.umsystem.edu/apml/>  ---
             Unsubscribe at <majordomo@seds.org>