Syntax:

-fluxtomag mag_constant offset

Example 1.
$ ./vartools -i Q1_public/kplr000757076-2009166043257_llc.fits \
    -readformat 0 1 10 11 \
    -fluxtomag 25.0 0 \
    -o kplr000757076-2009166043257_llc.asc.txt

/datab/jhartman/KeplerData/Q1/Q1_public/kplr000757076-2009166043257_llc.fits

Read in the binary fits Q1 Kepler public light curve for KIC 757076 (not included), convert it to flux using a zero-point magnitude of 25.0, and output the result to an ascii text file.

fluxtomag example

Fig 1. Example Kepler Light-Curve Converted to Magnitudes, the zero-point is such that a 25th magnitude star produces a count of 1, this does not correspond to the Kepler magnitude of the object.