When you get something on your sensor, you will have to confront the issue of safely cleaning it off. Note that the dust is not truly on the sensor, but on the front surface of an infrared blocking filter mounted in front of the sensor. This distinction, while true, is moot, as the front surface of this filter has a delicate coating and if scratched will forever be in front of your sensor.
Take a look these two sites:
Some other good links:
Photographic Solutions Inc. markets well endorsed products that are the "top of the line" in sensor cleaning. You can buy them from B and H photo (and others), note that the Eclipse solution may not be allowed to be shipped.
The first thing to try is to blow the dust off, and the best bet for this is a squeeze bulb, such as the Giottos air rocket. I bought what looks like a clone of this, but without the silly rocket fins and with a Canon logo.
If blowing the dust off with an air rocket doesn't get things clean, you have some questions to ask yourself. Anything beyond this involves a level of risk, and if you are all thumbs or prone to breaking things, you may want to track down an expert. One option is a Canon repair center (if you have a Canon camera). Another option is someone else who has cleaned and not ruined their own camera and who is willing to take the risk of messing up yours. Just remember that all experts are not created equal and I have heard of people who have waited weeks for an expert cleaning job and not been satisfied. Truth be known this is going to have to be done often enough (if you change lenses frequently) that you need to learn how to deal with it.
Beyond the squeeze bulb (air rocket), the next thing to try (and many will tell you to absolutely not do this!) is canned air. Make sure the nozzle NEVER points directly at the sensor. The nozzle itself has been known to fly out, and these bottles can spit drops of the liquid propellant. If you direct short blasts into the corners of the chamber, you will have plenty of high velocity "air" moving across the sensor, and the hope is that this will be more effective than the air rocket. I have done this twice now without ill effect (and with an overall reduction in the amount of dust), but you may not be so lucky.
Beyond this, we are involved with things that actually touch the sensor. Do not use Q-tips, kleenex, or any common household things. There are a number of brushes marketed explicitly for the purpose of cleaning sensors, and you should consider them as the next thing to try. Consider the Arctic Butterfly or other products from the company "visible dust". The latest model of the Arctic Butterfly is the 724, and it goes for about $105.00. The old 700 model sells for $71.00. Also recommended is a tool called the Brush Off from Photographic solutions, for about $60.00. Too much money for me at this point, so I have not explored this route.
There seems to be an oil coating on the inside of the sensor chamber, at least in some Canon cameras. It has been suggested that this is there to trap and hold dust particles (somewhat like fly paper). Be that as it may be, you want to be very careful not to let a brush or sensor wipe touch any part of the inside of the chamber, as you will then be transfering oil to the sensor by the very act of trying to clean it. Keep your tools clean! At the very least, store them in a zip lock bag when they are not in use (including the air rocket).
Wet cleaning is the final "brass knuckles" approach. The best course is to buy the wildly expensive sensor swabs from Photographic solutions (about $4.00 each), along with the "Eclipse" solution and follow the directions precisely. If you have access to lab grade methanol, you could use that instead of the eclipse solution. (The Eclipse solution is just very pure filtered methanol). You do NOT want to use "rubbing alcohol" as it contains various adulterants, including glycerine and will make you very sorry.
I have heard various stories about Pec Pads. Some say that you can use them to construct your own sensor swipes and save a lot of money. A reliable source says that he has found them to leave colored rings on the sensor, and is convinced that they have some kind of oil contaminant. Whether this is true of the batch he got, or that they are a bad choice, I cannot say at this point.
I went to a local photo shop and bought a kit marketed by American Recorder. The kit I bought (for APSC sensors) was the DSCK-117, and included 6 cleaning swabs and a 0.5 ounce bottle of cleaning fluid (methanol). It cost me $30, but I could have ordered it from B and H for $20.00, except that B and H won't ship a kit containing liquid, and I didn't have time before leaving on an important trip. I can buy another pack of 6 of their swabs (from B and H) for $15.00. The swabs are a single use item. You wipe once left to right, flip the pad and wipe a second time right to left, and check. If further work is needed, you open and use a second pad. (Each pad is individually sealed). These pads cost $2.50 as compared with $4.00 for the sensor swabs. B and H has a vast array of sensor cleaning products now, including some things like Pec Pads that are marketed just for sensor cleaning and are quite inexpensive. (Check the reviews, which are pretty good).
You can expect to have to do this more than once the first time to get a feel for handling the swab. My first attempt did not finish the final swipe and left a line of dust along the side of the sensor - it is important to force the swab to the very edge (and off of) the sensor. It is also important to press quite firmly (but don't be stupid!) The second swab yielded good results, although several small dust particles still remained.
I called it "good enough". I have done one wet cleaning in the 4 or 5 years I have had the camera.
Here is what the dust looked like before I started (but after blasting away with canned air).
Here we are after the first wet swipe:
Here we are after the second wet swipe (what I called "good enough"):
Uncle Tom's Digital Photography Info / tom@mmto.org