Re: I Camera Flatness

[Stupendous Man <richmond@a188-l009.rit.edu>]

  To answer the question, "How flat is the field of a camera",
I look at the mean value of the blank sky near the center,
and the mean value of the blank sky near the corners.  I then
calculate
                         (central - corner)
     non-flatness  =   ---------------------
                             central

  The images in TN 76 show that the worst spots by far are
the very corners of the image, in the area outside the 
lens design.  That makes sense.

  In the case of the I-band images in Data Disk 16, I find

                                              non-flatness
         center of image     ~  3120 ADU
     center of worst edge    ~  2950 ADU         5 percent   
         best corner         ~  2750 ADU        12
         worst corner        ~  2550 ADU        18 

  The field _is_ much better than ordinary lenses, that's for sure!
I'm not criticizing anyone.

                                          Michael Richmond