In fact, the dust what You can clean in home conditions, or without disassembling the whole camera at any camera is the dust from the surface of the low-pass filter.
There are many methods for cleaning, for myself i prefer blowing with compressed air, and if this is ot enough, then a wet cleaning with alcohol, some cotton swabs, and after this, as a last step the sweeping with a microfiber cloth on a wood stick (the plane end of a wood spoon from the coffeshops). The very tough dust pieces can be moved (dry) with a small brush with plastic bristles (which the artists use) + pressurized air.
But always under strict visual control of a stereo microscope with a 10x / 20x magnifying power.
Why is this important?
Because You have to be sure, that the “particle” which You are hunting on the surface is:
– not a small scratch, which is better not to scrape (You can damage definitely the surface)
– it is really on that outer surface.
It happened to me a few times before, that after cleaning, and controlling the surface with a strong LED-light and a lupe, there was dust on the test picture. This is mostly by the cameras which have on active dust removing system.
Here is the explanation, why:
Example 1, the good old 5d (Mk I)
Here the low pass filter is glued together in a single sheet, and it is mounted on the front of the sensor with no possibility of penetrating of air (with dust). No moving parts, just two parts in contact.
Example 2, the modern 5d MkII, with integrated ultrasonic cleaning system
As You see, the ultrasonic cleaning system vibrates only the front sheet – that means, that can not be glued together with the others. The result is, that some air and dust can penetrate under the first plate.
Yes, yes of course, there is a sealing frame there – but in the practice the dust is there inside.
And You can’t get it out from there.
What helps You in this case the microscope? Microscopes have a very thin depth of field. So, if You set the microscope on the surface of the outer filter, only the dust on it will be sharp – the rest will be blurred. And after this, You can check the dust under the outer plate turning the focus to the deeper layer. (I will make some pictures later) (once…)
The microscope which I use now is this:
It has a working distance of 100mm from the object – perfect for sensor cleaning, and even for soldering on the PCB-s (for 150 EUR).
Yesterday I’ve seen internal dust on a 40d too.