Re: [APML]: Beginner Needing Advise

[Steve Bell <sb635@delphi.com>]

Philip Perkins wrote:
> 
> 
> The whole CCD is 323 x 242 pixels (active area) and the guiding box is 36
> pixels square. On a 10" f/10 this translates to 29 arc seconds square. But
> the manual advises "to be safe, a good guide star should have no bright
> companions within a 1 arc minute radius" (48 arc seconds on a 10" f/10).
> This seems far more real - I believe that one or two of my "double star"
> gremlins have resulted from stars that far away. It seems that the 201XT may
> not have very good discrimination between stars of *nearly* the same
> brightness, although stars of substantially lower brightness shouldn't
> cause a problem. Maybe I'm being a bit harsh - the ST4 may be just the
> same.

Thanks for this info. I've asked the "guide box size" question a few times, and you are 
the only one that has 
given me an answer. Can you change the size of the guide box to something smaller, say 10 
by 10 pixels? A 36 by 
36 pixel box seems a bit large to me.  And I don't quite understand how a star outside 
the box could cause the 
201XT to shift to that star. I know that the SBIG autoguiders don't even digitize what's 
outside the guide box, 
so a star of near equal brightness, but outside of the guide box, does not confuse the 
SBIG autoguiders.

> 
> > What type of guidance exposure did you use on the 201XT for your successfull prime 
>focus shots? What size LX200
> > do you have?
> 
> Up until very recently, all exposures were between 40 mins and 1 hour. I
> only got the 201XT last June so I'm still a bit of a newbie and I've been
> taking lots of shortish exposures for experimental reasons. The weekend of
> the 13/14th we had fantastic astrophotgraphy weather and I got a perfect
> shot of M27 (1 hour on PPF-2). I also took a shot of M33 (2 hours, for the
> first time, also PPF-2). This came out almost perfect, but under high
> magnification the star points are slightly broader than ideal. I think this
> was because the corrector dewed slightly towards the end. As far as I can
> see, the 201XT should be good for shots of 3 hours or more. My LX200 is 10"
> f/10.
> 

What I was actually referring to by the words "guidance exposure" was how long of an 
exposure do you use on the 
201XT. This sets how frequently the 201XT issues guidance corrections. Given that, how 
long of a guidance 
exposure do you use? 1 sec, 5 sec, 10 sec, etc?

-- 
Clear skies,
Steve Bell
sb635@delphi.com
http://people.delphi.com/sb635 - Astrophoto page