The images on Disk 19-2 are V-band images of the same area of the sky: the center is near RA = 20:08:00, Dec = +04:30:00 (J2000). I noticed that there is actually a small shift in the position from frame to frame. In the ROW direction, which is roughly East-West,
stars move approx. -0.176 pixels per frame (to East)
-0.07 pixels per minute
-0.53 arcsec per minute
In the COL direction, which is roughly North-South,
stars move approx. +5.50 pixels per frame (to South)
+2.19 pixels per minute
+16.4 arcsec per minute
Why should stars drift from North to South? Tom's Mark IV must not quite be aligned properly. If the Mark IV were placed on a conventional mount, the diagnosis would be "the polar axis is pointing too far East".
I didn't do any flatfielding for these frames (although, now that I know that the field changes from frame to frame in this set, I could try to generate a flatfield frame from the follow images themselves), but did remove the dark current.
So, I found stars in all the 49 frames (my software ignored one of the 50 frames -- sorry), and used the stellar positions to define the image shifts needed to align them all. I broke up the field into a grid of 4x4 cells, and concentrated on just one cell for convenience. The cell's center is roughly RA = 20:11:00, Dec = +05:00:00 (J2000), and it's roughly 1 degree on a side. Below is a picture showing most of this cell, as well as a small box on which I'll concentrate.
The little box is only about 14 arcminutes on a side, which is just right for comparing to a portion of the Digitized Sky Survey (DSS) with the Aladdin tool from SIMBAD. Here's the DSS image from Aladdin:
I've circled seven stars (or, in the case of "G", a pair of stars) for which I can find magnitudes:
from Tycho-2 from USNO A2.0
star Bt Vt B R
-------------------------------------------------------
A 10.6 9.9 10.8 9.5
B 12.1 11.8 12.6 11.4
C 15.0 14.3
D 16.0 15.1
E 16.4 15.4
F 15.8 14.7
G 16.5 15.3
-------------------------------------------------------
Now, I tried coadding some of the images of this cell. Below, I show the results for 1 frame (no coadding), 11 frames, and 49 frames. The contrast may not be adjusted optimally in the pictures, but it gives a decent idea of the information in them. In each case, I show only a closeup of the same region as the Aladdin picture, above, with the same stars circled in red.
A single, 100 second, V-band image:
Result of coadding eleven, 100 second, V-band images:
Result of coadding forty-nine, 100 second, V-band images:
In this crowded field (not far from the summer Milky Way in Aquila), and with these particular images, it appears that one gains the most bang for the buck by co-adding a relatively small number of frames. Even the 49-image composite doesn't show clearly stars below R = 16, although we might blame some of that on the crowding.