Re: OPTICS FOR TASS: REFLECTOR OR REFRACTOR?

[Cameron Tully-Smith <cameron@zippy.sonoma.edu>]

Michael wanted me to reply to the list, so here goes...

At 09:42 AM 1/7/98 -0500, you wrote:
>  I've looked at your Hale-Bopp image (nice colors!), and it appears
>to me that there is very slight distortion from center to corner --
>on the order of a pixel or so of the scan.  Could you please send
>the following information to the TASS mailing list?

I looked at a larger version and at least part of this distortion
was probably induced by being slightly out of focus (darn it!)...
The bigger image (see below) shows little "donuts" near the HB nucleus,
which is how I found this.  Hopefully, the bigger image will help 
with figuring out how much of the distortion could be being out of focus.

>      1. the rough size of a pixel of your scan, in units of millimeters
>         or microns (so we can figure out how the teeny distortion in
>         your image will translate onto a CCD chip)

I've just put up a bigger scan of the image (see below).  The bigger
scan is 2574x1755.  Since the scan was made at 1950dpi, this means that
the image is (2574/1950)x(1755/1950) = 1.32 in. x .9 in. = 33.528mm x 22.86mm,
so each pixel is (33.528/2574) x (22.86/1755) ~= .013mm x .013mm.
Sorry if any of the above is incorrect... I'm a little doubtful, which
is why I showed my work.

>      2. the address of a picture of the blue sky and/or grey card,
>         so we can see the illumination across the field.

The bigger image of HB is at
http://www.wco.com/~shareimg/images/mak500/r54n9.jpg

A scan of the blue sky image (256 shades of gray off of a color (PPF)
negative)
is at http://www.wco.com/~shareimg/images/mak500/r229n7.jpg

Cameron :)
Cameron Tully-Smith
cameron@cs.sonoma.edu
http://www.cs.sonoma.edu/~cameron