Re: [APML]: Problems Doing Piggy Back Photography - Need Advise

[joneil@obs.empath.on.ca (Joseph O'Neil)]

James T Waters <James_T_Waters@ccm.ch.intel.com> writes:
>      
>      The problem is most of the pictures I have taken show stars in one 
>      corner of the picture having trails.  The trails are about 1.5 to 2 
>      star widths long.  Under examination with a 10x loop the images look 
>      fan shaped and are pointed towards the center of the picture. I don't 
>      think that this is field rotation because the trails are pointed 
>      towards the center.  Is this coma within the lens, differential 
>      flexure, camera axis not parallel to OTA... etc?  

Hi Jim;
       There are a couple of places to check, but I would start with the 
zoom lens first.  Generally, zooms are not noted for thier sharpness.  Do 
you have a fixed focus lens you can try?  even if you could borrow or 
rent one.
  Try two pictures, one after the other, same exposure, and see if there 
is any difference.

   The other possiblity wiht your lens is I have found amoung fixed focus 
lenses that they usually improve when you stop the lens down 1-2 stops.  
You could stop down your zoom, but then you are getting into F5.6 range.  
Kinda dark, but might be worth the try.

  One last question - your Meade, is it strictly alt-azimuth or is it on 
a wedge?  If it is NOT on a wedge, no matter how accurately it tracks, 
you will have some feild rotation.

joe