This pinhole delivers exactly what it should. A hole about 0.22mm, Brenweite 42mm (which is the Canon back focus also logical that estimated 40mm in describing not agree, but again the difference is more "pea counting driven"), Aperture f = 182 (although I rather with 166 expect, but that's practically no difference). The images are for cameras with KB sensor very nice and so "sharp" as one would expect from a pinhole (tested with EOS 5D and EOS 5D II). Here they look at cameras with APS-C sensor is not so good (tested with EOS 350D, 7D, 60D), also bothers me personally is the focal length, 42mm is on APS-C stop already more at the telephoto end. Unfortunately it is not possible because of the back focus in EF / EF to realize a smaller focal length (20mm would be extremely net, but that's at all possible only with the mirrorless systems).
A word about "dirt sensor": No. the opening is not closed by a glass. But one sensor can be cleaned. And if you (like DSLR quite common) lenses change comes also dust in the camera. Likewise, "pumps" virtually all lenses, either when zooming, or "only" when focusing air both through the lens, as well as by the camera (And that does not only affect the lenses change the length, but certainly also those who only shift lens groups). The pinhole One should certainly not be on the camera, if you stored (even if it is in your pocket) suspend, but as a camera cover (which is not tight) or a lens. But if you use it to take pictures, it is not really more prone than the "normal operation"
