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Digital dirt bugs
With digital cameras it is different. There is only one image recording material and that is your sensor. The sensor is stationary and you cannot change it like a new film cannister. When dirt sticks to your sensor you will see it on every image if you always use a small lens aperture.
Fortunately most dust or dirt that finds its way to the sensor if you are careful when you change lenses is small. To help reduce the problem most cameras (all that I know) have an anti-aliasing filter. This is mounted in front of the sensor so there is a little distance between the dirt and the sensor itself. Therefore when using a large aperture the dirt is so blurred that it is hard if not impossible to see on the image.
However, stopped down to f22 the lens has a greater depth of field both between the camera and the subject as well as the lens and the sensor. Look for these "bunnies" in the light or sky areas - that is where they will be most obvious. Big ones are black but many small ones are either dark circles or most annoyingly circles appearing like droplets of water.
What is the solution? Well as yet I am not convinced there are any easy solutions, but the recent vibrating sensor approach does help. However, if you persist in changing lenses frequently on a dusty airfield you may require a more direct approach or a professional clean. For dry dust a bulb blower may be the solution. A professional clean (£25-50 plus VAT or thereabouts) or the ultimate wet sensor swab may be the only answer for persistent sticky pollen blown in by the wind. The wet solution is not cheap, and the use once only clean room sealed swabs are very expensive. Alternatives such as vacuum and sensor brush require extra equipment. All need VERY careful use and can void your warranty, so I cannot recommend any of the DIY equipment (although I see most camera service laboratories use a combination with wet swabs too). As if a photographer does not have enough to carry!
No, I would like to see a more radical approach with the above as a last resort.
At this point some of you with compact fixed lens digital cameras might be thinking you do not have a problem, but dirt does accumulate in any camera even when completely sealed due to moving internal parts. Also many have smaller sensors magnifying any dirt problem that does arise.
I think manufacturers should consider several approaches, and the most important should be a means of isolating the sensor and mirror compartment with an airtight door just behind the lens mount, and another at the rear of each lens. Complicated? well no more complicated than the shutter protector on the front of a compact camera, and they could be made easily replaceable should they break. Any dirt could be designed to fall into a dirt trap in the camera body between both shutters where it could be easily removed later. By throat design, slight air pressure and anti-static materials as they come together should help reduce dirt ingestion.
Another alternative - (but more weight!) would be to make the bodies cheaper so we can have 2 or 3 and not change the lenses so often!!
SLR cameras have got cheaper, but if you want a full frame 35mm size sensor or greater then with lenses to go with them the total may come to a mortgage extension!
The anti-alias filter could be made easily replaceable so you can slide one out of the base and another one in, preferrably at a professional repair clean room facility with more LOCAL ones across the country (having travelled 30 miles to London to have my Canon recently professionally cleaned by Fixation Ltd at Vauxhall- a very good centre incidently for professional cameras).
This is where the big boys with medium format sensors backs score - they can change the sensor by changing the camera back! However at around £10,000 or even £20,000 a piece any profit for most photographers is going to go out the window unless they have a very big turnover. However perhaps eventually the sensors will become so cheap you can have 2 spares and replace a cartridge in the camera? But perhaps the best solution will be a roll of sensor material in a closed cassette? - back to film!
Some camera manufacturers have introduced software in-camera with the ability to record where fixed dust spots on the sensor or anti-aliasing filter and replace the black with surrounding colour on multi-images. This is useful but I suspect only works effectively when all images are similar or the marks are in an area of even colour, such as in a uniform sky. Photoshop also has a similar feature for post editing.