Originally posted by Wheatfield To the OP, I've been using Dust-Off for routine camera cleaning for some 4 decades, including nearly a decade of DSLR cameras. I have yet to damage a camera
If it works for you, then you are doing it right. There are two issues with most canned air - pressure and propellant.
Get too close especially with a new can, and the air pressure can damage delicate constructions. So long as the pressure is low enough (back up a bit), the pressure is no greater than one of the recommended blowers. Also, anytime a gas rapidly expands, it takes energy with it and chills everything. Unless you back off a bit so that surrounding air is pulled into the mixture, you will treat both the mirror and the sensor to a bit of thermal shock.
Nothing demonstrates this more than filling and emptying a scuba air tank. A full tank is about 200 times normal ambient atmospheric pressure. You can feel the tank warm when compressing the air and chill when the air decompresses. The tank can only radiate so much thermal change. So the faster you compress or decompress the air, the bigger the temperature change. No canned air that I've seen has any sort of regulator so the can noticeably chills in use. The longer the blast, the colder that air is when it hits your camera.
The second reason is the propellant. Canned air is not just air under pressure. Usually some form of very volatile gas is used to add 'umph'. More often than not, this is ether. If you have a sufficient stand off between the can and the object, the ether will dissipate before it gets into the camera. If it does get into the camera two things will happen. First, because the ether evaporates so quickly, it will chill the surface. That takes us back to potential issues with thermal shock. Second, if ether gets into any petroleum based lubricants in the camera it will rob your lubricant of some of it's more volatile components, so the remaining lubricant gets more sticky.
So Wheatfield - I applaud your success. For a lot of people, they will cram that canned air nozzle into the camera and blast away. Many will come to regret that technique. Those people would be far better served using a hand operated mechanical blower.