[APML] M33 exposure results

["Greg Hartke" <ghartke@adelphia.net>]

Hi, Alan,

I got the film back yesterday and looked at it. The damned thing showed some
field rotation. Field rotation! I've never made that mistake before so you
can imagine how peeved I was. I'll process it anyway for practice and to see
what can be done with this general length of exposure. One exposure was 155
minutes, the other 180 minutes. I'll try again as soon as the Moon permits;
M33 is a priority with me.

Quick comment: I took one look at the frames and was astounded by how thin
they were, even with that length of exposure. Let's see... I was shooting at
f/7, you were shooting at f/8. For a fixed focal ratio, the brightness
density (at the film plane) of an extended object will be the same at the
same exposure. The only thing that changes is the image scale as the focal
length changes. That said, my image should have been (8/7)^2 brighter than
yours, which is 1.31. That means my 155 minute exposure would be equivalent
to a 202 minute exposure by your f/8 system. However, I had to use a Tokai
LPS which introduced a filter factor. Assuming that factor to be 1.5, my 155
minute exposure would thus be equivalent  to 135 minutes on your system with
no filter. Hmm. Not so hot. Maybe that's why the image was so thin. Damn.
Did you think your image was thin?

Regards,

Greg

_______________________________________________
Astro-Photo mailing list
Astro-Photo@seds.org
http://seds.org/mailman/listinfo/astro-photo