Any optical system has distortion.
An evenly distributed grid of positions on the sky will not translate to an evenly spaced grid of positions on the detector. For many types of science the distortion will be small enough that it can be ignored. For other types of science it may be desirable to account for the distortion. With the latter in mind we have attempted to measure the distortion in normal NIRC images. Technique NIRC imaged the field of NGC 5634, a globular cluster which has been measured by George Gatewood of Allegheny Observatory, using the MAP astrometric instrument.