While obviously the results show that scratches and smudges can be practically unnoticeable, this article is a little misleading. For one, dust, smudges and sc

While obviously the results show that scratches and smudges can be practically unnoticeable, this article is a little misleading. For one, dust, smudges and scratches will affect the contrast of an image, and more noticeably with a deeper depth of field. I'm sure you've noticed this on cell phone shots with oil or makeup on the lens, as it's much more noticeable with deeper depths of field. This is simply because incident light will diffuse into all areas of the sensor/film, causing dark areas to get lighter than they should be. Additionally, the results here are incomplete. The author keeps his lens aperture wide open, which will keep depth of field pretty shallow. The deeper the depth of field (from smaller apertures, wider lenses, or smaller sensors) the more noticeable the scratches and dust will be, since it will localize the effects of the diffusion on the sensor/film. Deeper depths of field are often preferred by landscape photographers, to keep fore-, mid-, and background elements all in focus, which will make smudges/scratches more obvious. Additionally, many lenses are much sharper when stopped down (smaller apertures) from wide open. Same problem. I think it's a bit of a shame to see a perfectly good lens ("optically and mechanically fine"), which could have been donated or still sold at full cost (no photographer worth their salt cares about body scratches), be completely destroyed because the author wanted to prove a flawed point.