LOADING .ST8 IMAGES INTO CHARON:

Octavi, this one is a bit of a puzzler... generally, .STx images work
best in Charon because (unlike FITS images) they are _very_ "standardized".
Some programmers play odd games with the FITS format, but I've never seen
that happen with .STx images.

My standard advice (which I post here mostly in case anyone else has
had such problems): If Charon balks at an image, e-mail it to me, along
with your settings (in CHARON.DAT). I should then be able to duplicate
the problem and fix it.

I recommend this pretty strongly, and not just to fix the problem on
your end. I've found that there is a wide range of images out there, and
I like to have samples to test. Over the last few years, Charon has become
much better about handling all the weird variations in images, but people
still sometimes find ways to trip it up.

Also, in this case, you would be providing me with a nice way to test
astrometry/photometry in a Sloan ACR region. So I have a selfish motive
here, too <grin>.

I'd second Bob's suggestion (that you get the latest version of Charon,
which is much less user-abusive), but the message "image identified as
.st8 file" indicates that the image has been opened and the first line
of the header read.

PHOTOMETRIC RECALIBRATION:

Matt, you asked: "...Its not clear to me though in practical terms
how you know what plate you are on in a given area of sky. How do I
identify the plate in order to apply the correction?" You don't. I
don't expect that this recalibration would ever be used in a 'manual'
mode ("Hmmm, I'm on GSC plate 3X4... let's look through the table...
OK, I'll have to subtract .31 magnitudes from anything I measure in this
area.")

However, Guide, Charon, and any other software that uses the GSC
would be quite capable of doing this. Every GSC star comes with a plate
identifier. (Click on a star in Guide and ask for 'more info', and
its GSC plate is identified... in some cases, up to four plates, if
the star was imaged on multiple plates.)

-- Bill