Why do camera sensors need cleaning? It was never a problem with film!

Modern camera 'sensors', on cameras with interchangeable lenses, need to be cleaned periodically.

Why? Because they get dust on them.

With film, if you got some dust in your camera when you changed the lens, it would typically at most ruin one shot - the shot that the dust got on, because then the film would 'advance' and the dust would not be blocking the next portion of film - the next picture. In addition, the canisters of film had a felt brush that cleaned the film before it was pulled out of the canister, so any dust IN the canister (there should not have been any) would be removed. The purpose of the felt was to block light from getting into the film after you finished taking pictures.

Some cameras pulled ALL the film out, then as you took pictures it pulled the film inside the canister, so that if you accidentally opened the back of the camera, you would only ruin one or two pictures. Others (every one I owned) pulled the film out as you took pictures, then you wound it back in at the end. If you opened the camera back very briefly, you would ruin the last couple pictures and the tops and bottoms of all the pictures, if you left in open a few seconds, every picture you took was ruined.

But in either case, dust was not a huge problem because once it got on a piece of film, it would only ruin that specific shot (by blocking the light from getting to the film.)

When I first got into digital cameras (added them to my suite of 35mm and 4x5view view film cameras) around 1996. That first digital camera I had, used a one line sensor that 'scanned' the image while the shutter was open. It had problems of it's own and I found that taking pictures outdoors, it was better to hold the camera up-side-down. Why? because the sensor was 'blinded' by the light at the top and that caused streaks when it got to the darker image of the house. By turning it up-side-down, it took pictures from the ground up to the sky, resulting in far less streaks. The resolution was terrible in today's way of thinking, but by only have 320 sensors in a line, dust spots had to be pretty big for dust on the sensor to cause a problem. In other words, the pictures were so terrible that a little dust was not a problem!

From 1996 on, I bought one or two new digital cameras a year, because they were improving so much so fast, it was worth it to my businesses to have the newer equipment.

But now, for me starting in 2002, My Fuji S2 Pro cameras (I bought 3 of them) had a APS-C, slightly larger than the Canon ones, rectangular sensor. I bought that one because I had lots of great Nikon lenses and because the Nikon digital cameras of the day just didn't understand what a professional photographer wanted.

Nikon worried about saving battery life, instead of letting me get a picture, here is how it took a picture:

• My client had the perfect expression (perhaps a smile)
• I pressed the button to take the picture
• Nikon said "OK, NOW I'll wake up and start consuming battery. I didn't want to waste your battery before, even though your last picture was 1 second ago."
• Nikon said "Oh wait, before I take the picture, I probably should do a white balance check first - after all, every professional photographer wants really good quality images - far more important to be technically perfect than catching the right expression. Technical excellence over subject excellence you know!" Then their very slow computer would take some time to do that.
• Then when the white balance was done, it did some other checking - just to make sure everything was technically perfect.
• Then a half second or so after I pressed the button, when the client's expression was long gone, it took the picture.

And if you think I'm kidding - in 2003, I attended a meeting where Nikon apologized, and explained that the above is what was happening. They said "We didn't realize that professionals would rather replace batteries every few hours. We are sorry. We are going to do better." So maybe I'll buy a Nikon camera next go around.

Update 2012: They did do better. Their next line of cameras were constantly doing white balance when on so that, when you pushed the button, it took the picture and you got to catch the expression you wanted. But ... in 2002, Fuji S2 Pro was the best, not Nikon.

Anyway, I digress. The problem though with a sensor, be it Fuji, be it Nikon, be it Canon, be it any other manufacturer, was that once it gets dust or a smudge on it, it stays there, there is no 'film moving' to whisk the dust away.

While cameras continue to improve, I don't see this problem going away any time soon.

Update: Newer cameras have a vibration 'clean' that they do. Not perfect, but it has TWO benefits: First, dust will be in a different position from shot to shot, really this is better than every shot having a smudge or 'hair' in the same place. Second: in some cases they will get rid of some of the dust permanently if combined with other cleaning techniques. Unfortunately my Canon D20 does not have that feature.

What should you do? ideally, before every important shoot (like a wedding), and after each time you change lenses, you should check the sensor. You may have been wondering why I use 3 Fuji S2 Pro cameras ... the reason is two fold,

First, I don't ever want to photograph a wedding with just 1 camera and then find out some setting was wrong or the camera was defective, or it simply broke for whatever reason during or before the shoot.

Second, that way I can have 2 different or 3 different lenses, I can check the sensor before starting, and then make sure I do not introduce any dust in the camera by changing lenses during the wedding.

Hack: If you KNOW you have a smudge or hair or something and you simply can not fix it 'right now', a hack fix is this: make sure the defect is in a darker area of your picture - that way it will be invisible or nearly so. Places to avoid the defect: Sky, white and light colored areas, people's faces, hair of blond people. In other words - where the image is light and/or 'important'.