[APML] update: need help getting round stars

[dtlocke <dtlocke@flex.net>]

Bert, and everyone who's replied,

Thanks very much for all the advice/suggestions.  Tonight I bit the bullet and
performed my first tapping operation by adding another set screw to hold the STV
nose piece.  I've got a test running in the back yard right now.

I think I need to get an extension tube (or two) for the ST80 so I don't have to
rack the focuser out so far, even if my testing tonight shows promise.  I'll
also add another set screw.  I also figured out why I was using the reducer lens
(from the efinder) in the STV:  If I don't use the reducer then I don't have
enough back focus without using a diagonal.

So, a couple more questions:
1) Anyone know where to find an extension tube that would fit an ST80?  This
needs to thread into the focuser...  I had an extra from my Tak, and it's the
same size, but different thread pitch (which is really annoying...)
2) Where to get thumbscrews in small English unit sizes???

Thanks again,

-Dick


bert katzung wrote:

> Hi Dick:
> My 2 cents: I have used the Losmandy DSBS plate with the A-P 130 f6 and the
> A-P 80 f11 guidescope and it works very well; nice round stars. I wouldn't
> hesitate to drill and tap the end of the guidescope drawtube for another
> thumbscrew. In fact, I did this to provide extra insurance on the A-P
> guidescope, which starts out very solid. If the drawtube in your ST80 has to
> be racked out quite a ways, it may not be leaving much tube inside the outer
> barrel and this could result in changing flexure as the mount tracks. Less
> at the zenith, more as the torque increases away from the zenith. If I
> suspected this, I would add the second thumbscrew farther in from the end of
> the drawtube, to provide more leverage against flexure. Maybe even inboard
> of the focuser rack & pinion. Not having seen an ST up close I'm not sure
> what the physical possibilities are, but if you don't mind drilling and
> tapping (a pretty trivial operation), you could try these out before dumping
> the ST.
> Hope this helps....
> Bert
>
> Bert Katzung
> "When it was first said that the sun stood still
> and the world turned round, the common sense
> of mankind declared the doctrine false; but the
> old saying of Vox populi, vox Dei, as every philosopher
> knows, cannot be trusted in science." CHARLES DARWIN
> www.astronomy-images.com
>
> ----- Original Message -----
> From: "Richard Locke" <dtlocke@flex.net>
> To: <astro-photo@seds.org>
> Sent: Monday, 29 October, 2001 8:33 AM
> Subject: Re: [APML] need help getting round stars
>
> > If I do decide to upgrade my guide scope, what's a good solid one to get
> that will work out of the box?  I think AP has one, and that Orion is
> selling one as well.
> >
> > -Dick
> >
> > ---------- Original Message ----------------------------------
> > From: Matt BenDaniel <matt@starmatt.com>
> > Reply-To: astro-photo@seds.org
> > Date:  Mon, 29 Oct 2001 11:12:43 -0500
> >
> > >Richard Locke wrote:
> > >>...
> > >> Anyone else successfully using the Losmandy side saddle plates to
> guide?
> > >
> > >Richard,
> > >
> > >Like Bobby, I prefer a top-mounted guide scope.  It is easier to balance
> > >and is lighter and more compact.
> > >
> > >I did use the Losmandy DSBS for about a year and it worked fine.  It is
> > >a very solid unit and has no flexure.  The problem is that it has more
> > >weight and more angular intertia (especially in DEC), and it is more
> > >work to balance.
> > >
> > >I do not believe that the DSBS is the source of flexure in your
> > >situation.  Also the Losmandy plates and rings have worked very well for
> > >me.  I have not seen any indications of flexure with them.
> > >
> > >Again, I think the problem is the ST80 focuser or clamshell/plate
> > >interface.
>
> --  APML Archives at <http://astro.umsystem.edu/apml/>  ---
>              Unsubscribe at <majordomo@seds.org>


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