Good news! Canon just released a firmware update for the 5D Mark II, and it looks like the black dots problem is fixed. Before installing the new firmware, I setup my camera and a test subject and took a series of images. Then I installed the new 1.0.7 firmware without moving the camera and reshot the same images. You can see the comparisons below.

(The swatches are bigger than in the original test from a few weeks ago, because apparently I had my camera closer to the subject this time. I didn’t notice until afterwards, and there’s no way to rollback the firmware and reshoot.)

	Original (1.0.6) firmware	New (1.0.7) firmware
ISO 100
ISO 200
ISO 400
ISO 800
ISO 1600
ISO 3200
ISO 6400
ISO 12800
ISO 25600

So it looks like everything is okay. Hopefully people who photograph city lights and other problematic subjects will confirm my findings with real-world images.

Update: Just a word of caution…I normally wait a little while before installing new software, just in case the update actually introduces new problems. This time I rushed in so that I could serve as a guinea pig. Things seem to be fine so far, but if you aren’t bedeviled by black dots you might want to wait a week or two and see what happens.