people i have used an olympus om-1 film slr for many years, and dust never really was a big problem. now i am looking for a dslr. one of the camera's i am interested in is the pentax k20 because of its viewfinder and its solid build quality. then the k7 came along. one of the first tests of that was in a german magazine. in foto magazin 8-2009 in however there also was an article on camera based sensor cleaning.
from pentax they tested the km and the k7. where the km system showed virtually no effect at all, the k7 system ranked among the best.
my question now is how big an issue is dust on a sensor.
It depeneds on how often you change lenses, what conditions you use your camera in, whether you use zooms or primes etc...
I never had a big problem with sensor dust, despite always shuffling lenses around, but specks of dust are bound to appear sooner or later. There are several things you can do to clean the sensor if that happens (search these forums). In-camera sensor cleaning is a nice touch, but I wouldn't choose a body based on it - there are plenty of bigger differences between the K-7 and K20d.
If you shoot landscapes or macro dust is a pain in the neck because of the small apertures your using. The in-camera cleaning is only so good, it just moves the dust around. I use an Arctic Butterfly which gets the dust out of the camera.
K20D's sensor dust-removal advanced a little above the K10D's, which was already decent by virtue of its dust-resistance. So you should not have to see much dust on the sensor unless you change lenses in dusty environments often.
I've only had dust issues with one of the earliest of the Pentax DSLRs, my DS. Starting with the K series, Pentax started using an IR filter on the sensor which was coated to make it shed dust more easily. I have a K100DS, K10, K20, and K-7. My experience with all of these is that dust is rarely an issue, but the K20 dust removal seemed to work better than previous bodies, and the K-7 works the best. I have never had to wet clean any of my K series sensors, and I change lenses in less than favorable conditions quite a bit. I also average 3-5K shutter actuations a month, so it's not a matter of not using them a lot.
The cool thing about the K20 and K-7 is the "Dust Alert" feature, which will show you if and where there is any dust on the sensor. It's very effective and easy to use.
Dust is really not the issue it was 4 years ago. . .
thank you all for the input people. now all i have to decide is what to buy, a very good camera with a good lens k20 with 17-70 or the k7 with the standard kit lens
Because a sensor is an electronic device it tends to attract dust particles much more than our film cameras did. I probably went over a year before I ever noticed a dust spot on my K10D so the built in dust removal probably works pretty good. I have had to blow off the sensor only a couple of times and I change lenses a lot.
Well, I gotta say that k20d's dust removal has never got rid of any dust which has been a real problem with the photos. Always had to do wet cleaning with eclipse.
I had dust issues with my Nikons and the K100 but when I switched to the K-m with its anti static coating and SR based dust removal I haven't had to clean the sensor once. I was pretty amazed since the Pentax dust removal system isn't supposed to be that good.