I'm copying this response to the TASS maillist as well since Yoshida-san posted to both groups. The photometric problem mentioned at http://vsnet.aerith.net/misao/pixy/result/usno-photometry.html seems to be a non-issue to me. From what I can read, they are using USNO-A to calibrate CCD photometry with R-magnitude values from 5.7 to 14.9, mostly clustered around 10th magnitude. At the bright end, USNO-A magnitudes are not to be trusted _at all_. Remember, USNO-A comes from digitized POSS-I plates, where any star brighter than 14th magnitude is saturated, brighter than 12th magnitude has diffraction spikes, and certainly by 6th magnitude has haloes. I am also pretty confident that the match between, say, the 11.8mag CCD star and the 14.9mag USNO-A star is wrong. You should not be using USNO-A for stars brighter than 12th. A more appropriate catalog is Tycho-2, which is not saturated and has photoelectric values which are much more accurate than photographic ones in any case. Second, I doubt that Kadota-san's CCD has enough dynamic range to give good magnitudes at R=5.7 as well as R=14. Somewhere the detector is saturated; somewhere the signal/noise is so low that the photometry is suspect. You can't use a 6th magnitude star to calibrate photometry at 16th magnitude as suggested by their tables. Finally, the unfiltered CCD magnitudes cannot accurately be compared to a E-bandpass plate. That is probably the reason for the comment on the web page: >At a first glance, we can see that many stars are lacked in the USNO-A2.0 >in this field. In addition, it is hard to make match between >the stars on the image and stars on the chart. We can make match >easily between only a few very bright stars. and also the reason why the magnitude discrepancy for MisV1111 exists; the CCD is probably measuring I-band response for this red variable (and it may have been faint at the POSS-I epoch anyway). I don't see where stars are lacking in their example, just different brightness than what appears on the CCD image. This will often be the case in obscured regions such as the Galactic Plane. Certainly USNO-A photometry is poor, but give it a chance and use it where it is appropriate. Also, as Brian Skiff mentioned, you can usually find a nearby photometric sequence to calibrate the photographic values for the field of interest if you need better results. Arne