Sleepless In Seattle - Spotless In Subiaco - $ 5 Special...
Anyone with a digital camera knows the annoyance of discovering spots on your images - no-one more so than wildlife photographers who take pictures of leopards or giraffes. Thus you can understand my problem yesterday on the African savannah. The elephants were fine - the lions were fine - even the vulture was attractive and co-operative...but the giraffes had spots.
Not on the giraffes, mind. These were the Italian racing giraffes with the two-tone paint job and racing stripes. The problem was spots in the sky above them.
Normally this sort of thing is the result of dust on the sensor of the camera. Dust, skin flakes, insects, or shark teeth - they all leave distinctive shadows on evenly-lit portions of the scene. I noted them in the sky of the savannah shots. The irksome thing was they were happening with a camera body that had not had a lens change...and I was unwilling to believe that the camera company would have sent it out from the factory pre-dirty.
Well, nothing for it, but to carry on and resign myself to cloning it out in the computer - so I changed the lens to the next focal length and carried on. And the spots disappeared.
Working back to the first lens, I noted that it was an extreme wide angle...14mm. and that I was using it at f:22 - and focussed at the closest distance that it was capable of. So I looked round the front end of it and...found that there was a spot of dust on the front surface of the UV filter - right in the position of the mark. I experimented by removing the filter and re-taking the shot.
It is indeed possible to see the effect of a dirty filter if you have enough depth of field with your settings. So the moral is either take the filter off - or use one of the $ 5 special cleaning kits we have in our shop dump-bin to keep the blessed thing spotless.