Method and apparatus for varying the hole length of a parallel hole collimator, provides a variably configurable compound collimator for use in nuclear imaging. The collimator has a plurality of substantially parallel oriented collimator cores configured for transition between a contracted configuration and an expanded configuration, wherein a gap space between said collimator cores is greater in the expanded configuration than the contracted configuration. The maximum gap space is designed to prevent photons from one hole in the collimator from reaching the detector proximate an adjacent hole of the collimator.