Sensor Dust? There are ways of checking if your DSLR is in need of cleaning. 99% of the time the dust on the sensors is invisable in most photos...by "dust-mapping" you can determine how much and how large the dust paticles are.
1. Use the largest lens you have, at the farthest zoom setting.
2. Set mode to aperture-priority, usually Av on dial settings.
3. set focus to manual.
4. set ISO (equivalent to film-speeds/grain) to 100 ISO.
5. set exposure compensation to +2 or +3.
6 Stop the lens down as far as possible. (f/22 to f/32)
7. set lens focus to infinity. (If that feature is available.)
8. Point camera to featureless, well lightedbackground...ceilings and walls work well if they are light-colored. Make sure camera is not in focus and turn off any antishake or image-stabilization.
Take a picture, download it to your computer and examine it at 100% enlargement. The dust laden areas will show up clearly. Remember, these are extreme settings, don't be too surprized at the number of particles present...and are only a tool to help you guage how much accumulation occurs over time.
