Re: [APML] STV Guiding accuracy vs focus

["Jim Janusz" <jjanusz@dc.rr.com>]

Hi Rick, see below.....

snip

> Jim,
>
>
> I too have been using the eFinder successfully (1-2 arc sec is
successful),
> using a 200 mm finder scope.

With my old GM200 and good seeing it would guide at .5 arc second average on
the ST-V.  My new AP1200 was guiding at .2 and .3 arc seconds during some
testing last weekend.  Maybe your eFinder is not in perfect focus?


  But I'm trying to improve it. And in
> particular, I'm trying to get a zoom function, to allow both 50 mm "wide
> angle" finder mode, and a ~300 mm zoom mode for guiding.

I was thinking that an Olympus 135mm f2.8 that I have might have sharper
stars the the little eFinder and be easier to focus.  I have seen others
recommend short focal length refractors like the 80mm f4's that are around.

>
> Many people use off axis guiders, and the guide stars in these often look
> like seaguls don't they? I only defocused to diagnose the problem, and
then
> only such that the star was about 1.5 times minimum size.  It was not even
> obvious that it was out of focus.

I have a custom off axis guider for my 180 and it was a bear to use with the
ST-V because of focusing issues.  It has very slight star aberations because
it is before the field flattener and I think the -v is more critical the the
ST-4 which had no problems with them.

One thing I will say is the the ST-V works easiest with short focal length
guiding.  Longer fl's are much harder to settle down.


>
> I won't be using that old lens, but I'm not planning on using my expensive
> Nikon F2.8 80-200 mm lens for guiding either.  So I'm trying to understand
> what might be going on so that the next lens I acquire for the job will
> work.

I still say, use the best you have.

Jim

>
>
> Rick
>
> ----- Original Message -----
> snip


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