Rough calibration: based on image "main_align_2.fit", taken 


  Main ASI camera:


      Iapetus      (1256 , 716)

      Titan        (1258 , 982)
   ---------------------------------
      delta           -2  -266        


  So difference is approx 266 pixels.   According to Stellarium, 
the distance is 04m 40s = 280 arcsec.  Thus, plate scale is roughly

         280 arcsec  /  266 pixels  =  1.05  arcsec/pixel

  Wait -- that's the main camera.  And I get the value I expect.
Well, okay.  Let me look at the guider now.


  Image "guider_b.fit" has

      Iapetus      ( 358 ,   91 )

      Titan        ( 605 , 1117 )
   ---------------------------------
      delta          247 , 1026      

  
   So difference is about  1055 pixels = 280 arcsec

          280 arcsec / 1055 pixels  =  0.26  arcsec / pixel

   Guider image is binned 1x1, has size

         1280 x 960 pix  =  340 x 255  arcsec  =  5.7 x 4.3  arcmin


   Based on image from main camera with Saturn roughly centered,
and image from guider with Saturn roughly centered, the offset
can be determined from telescope shift between these two images.

 
     centered in guider:   20:33:04  -14:39:11

     centered in main:     20:31:33  -14:39:11

   Offset is 1320 arcsec = 22 arcmin, pretty much due East of the
center of the main camera's field of view.