These were made to be used with the Pyroelectric infrared sensors in security devices such as burglar alarms. These lens arrays were made by Fresnel Technologies, Inc. We don't have a clue about focal length or which devices these were made to fit. You get a set of 6, at least 4 have totally different characteristics such as focal length, beam configuration, etc. We have no way of testing them. Each of the 6 lenses is made up of multiple fresnel arrays.
