compressed air that is at too high a pressure can cause sensitive parts to become misaligned, moved, and damaged. canned air may also contain microaerosolized droplets of oils as well as the possibility of damage due to pressure. I echo the suggestion to use nothing other than a hand-squeezed blower. Hold the camera so that the lens opening is pointed downward - no point in blowing dust around only to have it settle out inside the camera. Make gravity be your friend.
to clean the focusing screen, follow the instructions on focusingscreen.com for removal and installation, paying particular attention to avoiding the use of anything metal or too hard a plastic, you do not want to scratch that thing up getting it out or back in. ("installation instruction" on the menu on the left.) I use my fingers, releasing the catch with my thumbnail and lifting the fresnel lens (it's not really a focusing screen) by its little tab. I wash it under lukewarm water with a tiny bit of dish detergent, rubbing the surface with nothing but the skin on my fingertips. That also strips the oils from my fingers, so after it's all dry (I use a seriously clean microfiber cloth very gently for that), I can put it back in with my fingers, since the detergent cleaned them up as well. I brush off the bottom of the prism with a painter's sable hair paintbrush, fan shape, and then blow it all out with the rocket blower. Make sure you note which side goes "up" before you take it out, and be sure to put it back exactly the same way.
When it gets bad such that the blower and sable-hair brush can't handle it, I clean the sensor with a bamboo chopstick. After you get over that initial shock, i'll point out that I take a small piece of that scrupulously clean microfiber cloth and wrap it around the end of the chopstick to make a swab (i.e., the bottom most part gets folded over the bottom of the chopstick a couple of times first, then wrapped around to make a bulbous "q-tip" shape. A couple of drops of lens cleaning fluid on the end of the swab applied very gently will clean the sensor really well. In my experience, you can't help but get droplets of oily crud on the sensor because of the use of petroleum based lubricants on internal moving parts.
As to changing lenses: first, keep in mind that dust is everywhere, ranging from very little in a semiconductor factory's clean room to lots and lots in a gravel quarry - the trick is to minimize the exposure, but whether you're in your house or sitting on your porch or out in the woods don't matter, as long as you're comfortable with how clean the air appears to be. Remember to loosen but not remove the rear lens cap on the lens you're going to install. Keep everything horizontal - if the openings are pointed up, you'll get stuff falling in; if down, you can't see what you're doing. Turn the camera off and leave it off for at least ten seconds prior to removing the lens - that allows the electrostatic charge on the sensor to dissapate - otherwise, it will attract dust like a cat's fur attracts a rubber balloon. Take the lens off, immediately switching the rear lens cap from one lens to the other, then install the replacement lens. Note: check both the front and back lenses of the replacement for cleanliness before you start. Plan your work, trivial as it may seem, in order to minimize the time in which the camera's open - the longer it sits open, the more dust is settling inside. Don't rush, but don't dawdle, either.
Last edited by dlhawes; 03-04-2022 at 08:13 AM.