Positive vs Negative USAF 1951 Targets: Which One to Use
A positive USAF 1951 target has opaque chrome bars on a clear background; a negative target has clear bars cut into a chrome field. The choice is set by your illumination: positive for brightfield and camera MTF, negative for darkfield, phase contrast, DIC and collimator or backlit work. What each is, how they image, a selection table by application, and the substrate that sets accuracy.