  We discuss in detail the photon structure function beyond the leading
logarithm approximation. Of special concern is the factorization scheme and the
hadronic input; we show how to naturally absorb large terms due to the MSbar
factorization scheme in a modified hadronic component. The effect of the charm
quark mass threshold is also discussed in relation to the phenomenology. A
comparison with data shows that the modified hadronic component can be
reasonably described by a VDM-type input.
