We used ZEMAX to measure the effects of forward scattering on the MTF and Spot Diagrams of an imaging system, quantifying the effects of veiling glare. We saw that ZEMAX accurately predicted that the effect of scattering is to redistribute light from a small spot to a large region of what had previously been a perfectly dark background.

The overall effect of scattering is to lower the contrast of the image and the system’s MTF, not through a blurring of the image spot (as is usually the case when MTF drops) but through an increase in background light.

We saw that, as expected, the decrease in MTF is proportional to the amount of light that was scattered nearby the image point, as shown in the Spot Diagrams.