Disclosed herein are devices and methods for modifying a conventional imager to have functional features similar to that of a lock-in camera. Optical mask devices are configured to be coupled to conventional imager sensors and the configuration of the mask devices can be adjusted to acquire image data in rapid succession. One variation of an optical mask device comprises a substrate comprising a pattern of light-blocking and light-transmitting regions and an attachment structure for coupling the optical mask device to the imager. The substrate is configured to adjust the position of the light-blocking regions and light-transmitting regions relative to the light-sensing region of the imager based on a set of one or more predetermined substrate configurations. In some variations, the mask device and/or the imager sensor may be mechanically moved relative to each other based on the set of one or more predetermined substrate configurations.
