The real test was the second one. It answered some of my most interesting questions, how much dust really is inside the camera, how it affect the picture, when we see it and how do we clean it.

Despite my D60 not being cleaned for three years, dust spots on my photos were very rarely disturbing. It happened mostly on the pictures of the sky at high apertures, which I've talked before. I've found that the biggest problem is at apertures 8 and 11, when dust spots were smudged across a larger area, making some kind of a soft circle. At these cases I've used some software for editing photos and removed the circles. I didn't make a fuss about it, just simply solved the problem. Taking my camera back to the store to fix the problem in this case wouldn't be worth it, as the dust might come any moment after the sensor has been just cleaned. The dust is not just on the sensor, it's everywhere inside the camera, so sooner or later it will fall on the sensor.

When testing cleaning brushes, I've photographed directly into the sky at all apertures of the lens EF 50mm f/2.5 macro, from 2.5 to 32.
At aperture 2.5 I couldn't see any dust spots even after heavy software manipulation. At aperture 8 there were some soft spots, which became more defined after tonal readjustments. At f/16 some spots were visible even without shifting the levels and at aperture 32, spots were of course there, easy to see.
So that's the dust I carried in my camera for three years. Most time I didn't even notice it, because I seldom use aperture 22 or 32. On usual shots you see it only after shifting the levels in software, but doing that makes the photo useless. On the other hand, photographing uniform areas with few or no detail, dust spots can be visible and can cause problems. To find out for how long I've carried the dust in my camera, I've searched for old photos, where the dust could be seen.

Occasionally, I've faced dust spots on my photos even before, but now that I was systematically looking for them, it was much easier to find them. To find the dust, you just have to follow some simple steps (shift levels of tonally uniform areas of the photo), but usually the dust will never be seen.

Still, why would I want any spots on my photos, if I could remove them easily enough with special brushes like Sensor Brush is. Many users like them for making the job well done.
When testing cameras I rarely read the manuals, but when I tested sensors brushes and CO2 spray, I read them all. They are short, but essential for successful cleaning. The most important thing is to have full battery. Otherwise we could damage the shutter and the mirror, as the shutter closes when the battery is empty and can catch our brush while we're sweeping the sensor. New cameras have a function called »Sensor Cleaning«, which opens the shutter and releases it only when we turn off the camera or the batteries are drained. So be sure you have inserted full batteries in your camera. Older cameras like my EOS D60 do not have this function, so you have to use the Bulb setting and manually hold the shutter release button until the cleaning is completed. This makes the job a bit more difficult.

For the cleaning of all of my test cameras EOS 350D and my D60, I've chosen the brush SB-16, which is suitable for APS-C sized sensors (crop factor 1.5x, 1.6x). Sensor Brush tools were at first used in laboratories for removing dust from the glass of microscopes. The dust is much bigger problem there, as it is magnified. This means that these brushes were already proved to be efficient, without leaving any marks or smudges on the cleaning surface. Brush hairs are positively electrified, while the dust is negatively electrified. This makes sweeping even more efficient.

After my experiences with 350D cameras, I've finally cleaned my D60, where I had to use the bulb function, as D60 doesn't have a »sensor cleaning« function. Since each cleaning takes only a couple of seconds, it can be repeated a number of times and with an extra care, with only a half full battery.

After some practice with the sweeping, I've cleaned my three year old EOS D60. Here's the result at aperture 16. For what's left, I don't even need to clean it I think. You would?