In a recent post, I showed how a UV filter in low light can produce ghosting and flare. You can also get some unwanted results if dust and lint is on your lens. Most dust is not a problem; even small scratches may not appear in your image. But in a high contrast situation, that dust can have a big impact. Take a look at this photo:
You can see on the right side of the image a large white spot. This is, of course, an area of high contrast between the bright window and dark curtain. Operating with a narrow aperture (I’m typically at f/10) can also reveal imperfections. If you have dust on your sensor, for example, it will be more noticeable at f/22 than at f/4. When I saw this, I immediately checked the front of my lens and noticed some dust and lint. I blew it off with an air blower then used the brush on the LensPen. Then I took another shot:
Just like that, it’s gone. I did not use Photoshop to alter the “after” image; I simply cleaned out the dust and lint on my lens. The image still needs work and is not the final version I delivered to the client. But if you ever spot the same problem on your images, it wouldn’t hurt to check your lens for dust. Oh, a couple of tips: do not use your breath to blow on the lens and do not use compressed air.