U,B color‐magnitude diagram of 1730 sources from the J0053+1234 field, showing 178 sources with only U,B detections (small open circles), and 1552 with UBRI photometry (small dots). Sources with spectroscopic observations are shown as triangles, they comprise 60 confirmed quasars (filled triangles) and 62 non‐quasistellar objects (open triangles). One quarter (30/122) of the spectroscopic targets are UB‐only sources, and 16 of these are confirmed quasars. The dashed line shows the blue ﹩U-B﹩ color cut for objects with R and I nondetections. The photometry presented here has been corrected for air mass and color terms, as well as Galactic extinction using the Schlegel et al. (1998) reddening maps. We show the mean systematic error in photometry in the top right‐hand box. The random photometric errors as a function of B magnitude are given at the bottom.