DSLR Sensor dust detector

Example with a Canon 300D

The tube is a Celestron tele-extendeur (42mm thread) on a Canon EOS T adaptor The black hard plastic sheet is glued at the end then cut at size and a ~1.5mm hole is done in its center
   
left image is a crop of a test picture of a white wall in daylight. click on it for full uncropped picture done with this "lens" !