I have an instrument that has a moving stage. The instrument takes readings in a fixed location and the stage moves to align the sample under the instrument. I would like to sprinkle sand on the stage and have an optical sensor tell me if there is a sample there or not (background). If there is a sample there, I would like to take a reading. If there is no sample there, I want the stage to move to the next area that has a sample.
I am not looking to find an optical sensor for the grains of sand. I would like to find an optical sensor to put on top of the eyepiece lens because you can easily see if there is a sample there or not. Background would be tape so I can choose whatever color that would be best. I am looking for the sensor to determine "yes there is a sample there" or "no sample".