A black smudge/dot first appeared on one of my images shot with a white background, and since I was outside taking photos, I figured I had captured a bug flying by.
The playback images are small, and depending on the focus, the dot sometimes didn't show at all - especially on images with a multi-colored background.
After spying the dot while processing the images on the PC, a pattern began to develop. My lens was clean - but it didn't show through the lens to begin with.
My camera manual had instructions for locking up the mirror and then removing the lens in order to get to the sensor. I was nervous - damaging the sensor makes the camera useless.
After removing the lens, the sensor is right there - and so was that spot I was seeing on my images. Since I only have a blower at this time, I held the camera with the face pointing down, and I used the blower to see if the spot was loose. That dust came right off with a couple of puffs.
I can see that I will need to purchase some eclipse fluid and some swabbers to do a wet-clean at some point. For some reason this does not make me nervous. The sensor was easy to get to and as long as I have the right tools, I can no reason to dread cleaning it. What a relief!