Do your shots suffer from dust spots? Not sure, well if you’re getting a dark spot/s on your images, in the same place/s, it could be that you’ve got a speck of dust on your camera’s image sensor. How did that happen? Well, most likely when you changed lenses, some dust got attracted into the camera body and has now made its way onto your sensor.
If you want to determine for sure if you’ve got dust spots, try this technique:
Using a 50mm or longer focal length on your DSLR, find an even, light coloured, evenly-lit background for a test shot – a blue sky, a white wall, even just a piece of paper. Select manual focus and set the focus to to make your selected subject completely out of focus. The aim is to see the dust, not the wall/sky/piece of paper. Don’t worry a steady image either, a bit of motion blur will actually help in this case. Perhaps use focus at infinity and turn off image stabilisation if you it. On the camera, set your exposure mode to aperture priority (usually AV), ISO to 100 and most importantly, set the aperture to a very narrow, i.e. a high number – at least to f/22 or more if you have it. Very wide apertures won’t show up dust spots as well, if at all. Take the test picture.
If your sensor is dirty, you will see spots in your test image. They are especially easy to see if you load the test shot into your computer and increase the contrast.
So, you’ve got spots – what now? Can you clean the sensor?
Sensor cleaning is best carried out by professionals – they have the right kit, experience and work in (almost) dust free environments. If you can’t put up with the dust spots, get your camera cleaned by those that are setup to do so. (NB. there are lots of instructions on the web on how to do it yourself and kits to buy – but they all carry a risk!).