of objects with color indices $B-V < 0$ (see Fig.3). Observations in the R filter (the second approximation) allow us to select among such blue “candidates” only the ones, which must be below the line $V-R=0$. In Fig.4 it is well seen how the objects with $B-V \leq 0$ (crosses) “scatter” over the diagram $(V-
R)/V$. A subsequent test of blue in $B-V$ objects with the help of the criterion $V-R<0$ reduces sharply large number of such “candidates” with the expected black body (“stellar”) distribution over the $B, V, R$ fluxes even without a careful analysis of their profiles for the purpose of revealing stellar likeness or extended character of an object.

As is seen from Figs. 3,4 and Table 2, the limits, from which the level of $S/N$ is greater than 4 for each of the [*B, V, R*]{} filters in the average for the whole mosaic, are equal correspondingly to $B=25.7,\ V=25.7$ (and $R=25.6$). Thus, from the aforesaid it might be assumed that almost all obviously blue in $B-V$ objects studied up to $B\approx25.2$ (see Fig.3) are too red in color index $V - R$ to attribute them confidently (with $S/N > 4$) to objects with the black–body 