The DVO photcodes define a photometric system, consisting of a detector, a filter, and a telescope.

Many DVO commands which accept a photcode as an argument allow for the photcode name to be appended with a modifier which changes slightly the type of magnitude returned to the user.

The type of photcode is specified by adding :type to a photcode. Valid types consist of:

- inst : instrumental magnitude
- cat : catalog magnitude = inst + nominal ZP
- sys : system magnitude = color + airmass corrected mag
- rel : relative magnitude = applies color, airmass, and relative magnitude offset corrections
- cal : calibrated magnitude : applies zero-point and color terms from dependent to primary/secondary magnitude system)
- ref : reference system

This page needs serious work to clarify the meaning of a photcode, and the selection criteria