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The simplest way is to use the difference between PSFMag and KronMag. This has the advantage that it is available for all objects in the survey and in all the main tables.
 | This example is from a stack sample around Abell 1656 matched to SDSS and coloured by SDSS classification (red - stars; black - galaxies). A cut in iPSFMag-iKronMag of 0.05 (shown) does a reasonable job of separating stars and galaxies. |
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Either momentsR1 or KronRad can be used as a separator (KronRad is 2.5*momentsR1 so it doesn't matter which you use (again from StackObjectAttributes or StackObjectView).
 | Same sample as above, now using log10(imomentR1) as the separator. |
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You can also try momentRH, which is the NOT the half light radius, but the expectation value of r^0.5 :(again from StackObjectAttributes or StackObjectView) .
 | Same sample as above, but noe now with log10(imomentRH) as the separator. |
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