[AJames]

Originally Posted by Dennis

A couple of the images posted in the response above show stars at magnitude 19.11, 19.13 and 19.18 if the USNO figures are accurate.
These were taken with a C9.25 and Vixen 4" refractor from suburban skies in Brisbane. I have also managed to get down to mag 19 with my Vixen 4” refractor and the ST7 from suburban Brisbane; again, if the USNO values are correct.
Cheers
Dennis

Well, if true then it might be easier that stated. The magnitudes you quote, do you know what what measurements these are? I know the CCD is pretty good gaining fainter stars, but the limiting problem is likely the sky brightness.
There are some visual magnitude calibration fields that I've seen, but I'll have to think exactly where I've seen them, but the biggest problem is that UBV photometry is not common for 19th magnitude stars - probably something to do with the light absorption of the filters themselves.
Are the USNO Values you refer too are from the B2? If it is, the values here they are not exactly visual magnitude equivalents.
Another possibility to to image the field with Eris (or some other asteroid) in it, then image it again after several nights, and see if one of the stars has moved. Another would be getting a recent image of the star field with Eris in it, then compare the field stars visible with your own image. (Eris is slightly red as well, which might pose addition difficulties.)
The mags (and graph) quoted at;
http://homepage.mac.com/andjames/PageEris002.htm
Have come from NASA's HORIZON Ephemeris.
My views have been; "It may also be possible to record the body by amateur deep CCD images, though its detection likely requires at least 30cm to 40cm apertures."
If you do achieve this it would be most impressive.

Andrew