jm76237 wrote:
An how often does one clean the sensor?
I'll say it again: whenever it needs it.
Dust on the sensor can be mitigated to some extent in postprocessing, so unless you're really anal about it, you don't need to clean your sensor on a schedule. There are, however, some things you can do to increase the time intervals between full-out cleaning.
If your camera has a "sensor shaker", set it to go on every time the camera is turned on or off or both.
If you start to notice a few small dust spots, try to blow out the camera. For this you want something like a rocket blower, not a can of compressed dusting gas. The compressed gas is meant for cleaning your keyboard, not your camera. Keep your rocket blower in the package it came in, or in a plastic bag to keep dust out as much as possible. When you get ready to use it, give it a few squeezes to blow any dust out of the nozzle. Take the lens off your camera body, hold it with the opening pointing down, and blow out the mirror box. Then use "mirror up for cleaning" and blow out the sensor. When blowing into the camera body be sure to keep the blower nozzle outside the body so you don't accidentally scrape it against something.
Note that it's important to use "mirror up for cleaning" instead of trying to use the Bulb setting or something similar. First of all, once you use that setting the shutter is not likely to close when you don't expect it. Maybe more importantly, the power is turned off on the sensor when using that sensor. That reduces the possibility of static charges attracting the dust that is flying around while you're blowing it out.
I try the blower up to three times to get the dust out. If it doesn't work after three tries, it's time for more aggressive cleaning. Wet cleaning can be scary the first time. After that, it's a piece of cake. Lots of threads on wet cleaning so I won't go into it here.
When checking for dust, many people recommend setting a small aperture and taking a picture of the sky. That's fine if you're doing it during the daytime or if your sky doesn't have a lot of clouds in it, but there's a better way.
Sit down at your desk with your computer and put all the stuff you're going to use for cleaning on the desk nearby. Bring up a blank page on your word processor (ideally white, but any fairly light solid color will really do the job). Set your camera to a small aperture and set it to manual focus, focus at infinity. Place your camera as close to the screen as you can and take a shot. Then you can look at the image to see if you have objectionable dust. The advantage of this method is that you can do it at night, you don't need a white wall without any texture, and you can do it sitting at your desk without going outdoors to check for dust.