A scattered light point spread function is measured for use in fabricating microelectronic and micromechanical devices using photolithography. In one example, a photosensitive layer of a microelectronic substrate is exposed through a test mask, the test mask having a series of differently sized patterns, each pattern surrounding a central monitor feature, the differently sized patterns each being evenly distributed about its respective central monitor feature. An indication of the exposure of the photosensitive layer is measured for a plurality of the series of differently sized patterns. The exposure indication is compared to the pattern size. The comparison is fitted to a function and the function is applied in correcting photolithography mask layouts.