This information was posted previously by BigMike. I plan to clean my sensor using the information he provided.
Most of you folks here know me from being a longtime member, and many know that I have been an electronic technician for over 35 years, so I would not give you this suggestion without being certain of the facts. Actually it's Canon that knows the fact, and on this they are right. The book suggest blowing dust off your sensor with a bulb blower. I have been doing that for quite some time, and if done properly, is safer and easier than using pecpads and fluid, and is extremely effective. I have not had to touch my sensor with anything but air for a long time. The other benefit is you can quickly get rid of hair and dust in the viewfinder using the same method.
The trick is to use a device that puts out a small blast of air. I know some of you have mentioned using devices that put out far more air than is needed, and can end up making things worse, by blowing the dust all over the place. Here's my suggestion on cleaning: First, buy a small nasal aspirator. You can buy them at any drug or food store in the baby section. It is used for extracting mucus from a baby's nose. It pushes the perfect amount of air. Take the lens off of your camera. Tilt the front of the camera downward, and give a few blasts to the mirror and the focusing screen above it. This will remove any hair and dust that shows up in the viewfinder. Next, go into the menu and turn on the sensor cleaning option to lock the mirror up. Again, face the camera downward, and give at least 10 to 15 blast of air, at about two inches from your sensor. With each blast, move to a different area of the sensor. Then, turn off the camera, and attach your lens. See if you viewfinder is clean. Then take a few test shots of a blue sky in aperture mode, at between F18 to F22. If there is any remaining dust in your viewfinder, or in your test pictures, repeat the procedure. Most times it will get it all on the first cleaning, but for stubborn dust and dirt, another cleaning may be necessary. I have found this method to be extremely effective and easy to apply, even out in the field. If a speck of very stubborn dust requires pecpads and fluid, then use it, but I think you will find that you will not require the pecpad method 95 percent of the time, if you keep things clean with the light blast of air method. Thanks for reading.
(link to thread where he posted the information)
Your CMOS is most likely dirty. This is usually more noticeable
when you are using a aperture. Try an unfocused low aperture shot
of a white wall to see it more clearly. When you clean your CMOS,
the corresponding area is inverted.
Get some cleaning equipment before you start with this process, or
you'll make it worse.
This topic has been posted before but ive just taken a series of
sky shots most of which have a strange black smudge in the same
place.Ive only had my camera two weeks and have rarely used it
yet,I keep it in a camera bag so i cant understand if its a sensor
problem .Any ideas please