focus shift
Definition: Change in the position of plane of best focus. * In zoom lenses, focus may change slightly with change of focal length. This is tolerated in auto-focus compact cameras in order to keep costs down: focus is finalized just before capture. * In other lenses, focus may shift with change in aperture -- a serious problem if it occurs in enlarging lenses -- often due to under-corrected spherical aberration.
Previous Term: focus control Next Term: f-theta lens