In this paper

we discuss the techniques of stray light analysis in optical system when the ghost image happens.In the meantime

two different surface theories are given

they can describe surface scattering character ics

which are typical in optical system.The first is correctly accounting for shadowing-masking

which based on mirror-like facets reflection theory

with surface roughness small compare to wavelength.The second is a rigorous theory which is based on vector—perturbation theory.Then

the utility of these two models of stray light calculations is discussed.