Apparatus for receiving light containing image-representative information, and low-pass filtering the light. A pellicle is positioned in the path of the light. At least one transducer is coupled with the pellicle and an AC electrical signal is applied to the transducer to establish waves in the pellicle....http://www.google.ca/patents/US6356379?utm_source=gb-gplus-sharePatent US6356379 - Adjustable opto-acoustical low pass filter and technique
