Re: [APML]: Beginner Needing Advise

["Philip Perkins" <philip.perkins@pop3.hiway.co.uk>]

Steve
 
> Phillip, do you know how big (in pixels by pixels) is the guiding box for the 201XT? I 
>can't imagine it uses 
> the *whole* CCD, because that would be terribly inefficient.

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.

> 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. 

Dark skies, beautiful images

Philip Perkins  --  philip.perkins@pop3.hiway.co.uk
51 27'N 1 36'W  --  dark skies, dark clouds (mostly)