Have you ever had this: While shooting out in the middle of nowhere, you notice a phenomena on your photograph in the sky. As it turns out, this phenomena sits on every photo in the exact same spot. From here on you can go the safe route and have your DSLR cleaned. But what if there is no time, or what if there is no place to have it serviced nearby and you did not bring any cleaning gear? In this post I will show how to clean your DSLR sensor using just a cotton swab.
Disclaimer
Even though I think it is VERY difficult to damage your camera using a cotton swab, I must warn you that all things you do based on the information in this post are at your own risk. If you are not comfortable with steps described here, just have your camera serviced at a Canon service point.
That said, I think you do have a chance to damage your camera if you manage to have the mirror collide with a cotton swab. I do not think you have to worry about the sensor itself: You will not be touching the actual sensor, but merely the filter that sits in front of the sensor. And that filter is a glass surface. So go out with a cotton swab, and try to scratch a window of your house; I think you will not succeed, just as you will not manage to scratch your sensor. There is one important exception to the rule though: If you manage to have a grain of sand on the swab or your sensor, then you obviously will risk scratching it while cleaning. I personally have never seen sand clinging to a sensor though, it must be VERY fine grained in order to be able to, but I just want to make you aware that something like this could potentially happen.
How do you know if your sensor is dirty
For some reasons sensors get dirty. Sometimes they stay clean for months, then all of a sudden it is like someone sneezed directly onto it. I have an example here of a very dirty sensor which I noticed during a macro shoot. The top picture is a shot with flash (so the background is dark) which I overexposed for the purpose of showing dirt, the bottom picture is a shot without flash, which I darkened for the same reason:

Two shots clearly showing a dirty sensor: the top picture has been overexposed, the bottom one underexposed to maximize visibility of the dirt on the sensor. The red arrows clearly indicate smudges that are in the EXACT same spot even though the angle on the fly is totally different.
As you can see, the arrows clearly show smudges (and even a hair like shape) on the pictures that are in the exact same position for both shots. This is a clear indicator that the sensor is indeed READ MORE »