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I was just reading the question How many actuations are "too many actuations"? and trying to figure out what a shutter "actuation" actually is.

The only thing I can guess is that it's the number of times the shutter is released and restored — i.e. how many photos the camera has taken — but values of 50-100k don't seem like that many. Is that really what it is?

Why is the word "actuations" used here? Is it a term manufacturers use to sound fancy or to mask that modern cameras might fail after 100,000 images?

What happens when 100k is reached (or whatever the actual lifespan is) — does the shutter fail in a way that damages the camera? Can it be repaired, or is it effectively the end of that camera body's life?

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"...100k doesn't seem that many." If you were to use one camera body for full-time work and snapped one photo a minute throughout every working day, it would still take you two years to get to 100k. The Camera Shutter Life Expectancy link given in the thread you reference shows that most shutters on popular DSLRs tend to last for much more than 100k, some up to 5,000,000 or more. (That's one shot a second over two years of full-time work.) –  whuber Oct 9 '10 at 0:20
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They'd be pretty short working days! But yes 100,000 is an awful lot! –  Matt Grum Oct 9 '10 at 11:36
    
I've read on dpreview.com, which Nikon d5100 has 100 000 Shutter Cycles. –  user6059 Jul 24 '11 at 10:55

4 Answers 4

ac·tu·ate
[ak-choo-eyt]
–verb (used with object), -at·ed, -at·ing.
1. to incite or move to action; impel; motivate: actuated by selfish motives.
2. to put into action; start a process; turn on: to actuate a machine.

You pretty much have it. A shutter "actuation" is the opening and closing of the shutter when a picture is taken. It should be noted that you can actuate the shutter for other purposes, most notably to enable sensor cleaning in many modern DSLR cameras. The total actuation count of a camera may be more than the total number of pictures it has taken, so it is important to differentiate between the number of photos and the number of actuations.

Generally speaking, I personally find shutters that have less than 50,000 actuations have too few. On average, I figure I take 500-700 pictures a week when I am active (I've had a couple inactive periods this year, so I'm a bit under that for the year.) In a single year, on average, that would be about 30,000 shutter actuations. A camera with a shutter rating of 50,000 actuations would probably last me two years, maybe three. For a low-end DSLR, three years is probably not too bad, but it wouldn't hold up under professional use. A pro could very likely burn through 50,000 actuations in a year or less, under much more strenuous situations. Shutter lifetimes of 300,000 actuations would probably hold up for 3-4 years of professional use in the real world. Many low- and mid-range DSLR's these days have shutter lifetimes of 100,000 to 150,000 actuations, and under normal usage, a camera body should last for quite a number of years.

The type of photography you do can have an effect on shutter lifetime. If you are an avid sports photographer that makes extensive use of burst mode on your camera and takes several thousand shots a week, a 300,000 actuation shutter may only last 2-3 years. On the other hand, if you are more the landscape photography type, who may snap a photo once every few minutes, and only a few at a time, a 150,000 actuation shutter may last you for a decade.

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While technically you're right on photo count being different than actuation count, making a photo is overwhelmingly the dominant cause of actuations, so for all practical purposes they are the same. –  Reid Oct 9 '10 at 3:54

In my experience the shutter tends to fail gradually, i.e. it becomes unreliable shooting at high speeds, the first and second curtains can get out of sync, giving you inaccurate shutter speeds. It can fail completely in one go, but you usually get some warning. The shutter is very light and delicate so it's unlikely to do any damage when it goes! And yes you can have it replaced without writing off the body!

100,000 actuations may not sound that many, but consider that the shutter design originates from the days of 35mm film SLRs. At $10 for a roll of film + $10 for development, reaching 100k on the shutter would cost you two million dollars in development! I think that if digital had been around earlier we'd see a lot more electronic shutters.

Finally, as mentioned in this question the rated shutter count is the average number. Component failure usually follows what's called the bathtub curve, i.e. the failure rate vs.number of actuations is initially high then it flattens out before increasing again at the end of the lifetime.

@Rowland: shutter lifetime, were it modelled as a random variable would be expected to follow the normal distribution, however I'm talking about failure rate i.e. the chance the shutter will fail at a given point in time (if this looked like the bell curve it would mean the chance of a shutter lasting forever would be almost 100%!). Assuming random failures the graph would look like the cumulative version of the normal distribution.

However, failures are usually down to two factors, wear and tear (that accumulates over time) and manufacturing faults. If something has a manufacturing fault it will tend to fail immediately or very soon. If you again assume these two causes are random, and add the distributions together you get the bathtub curve which is most often used in dependability analysis.

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I would expect the curve to follow a normal distribution? (i.e. a bell curve) –  Rowland Shaw Oct 10 '10 at 16:07
    
@Rowland had to reply to you at the end of my answer as it was too long to put in a comment! –  Matt Grum Oct 10 '10 at 17:53
    
I think what Rowland meant was that shutter failures tend to occur around the time they are expected to, with failures happening earlier or later occurring less and less. Think of it similar to IQ: You have the average IQ, 100, occurring most frequently, plotted center-graph, with IQ's of 80 and 120 occurring less often, and IQ's of 75 or 135 even less often, and anything beyond that a tiny fraction of the time. A shutter rated for 100k should fail at 50k or 150k less often than 100k, and 25k or 175k even less often, hence...a bell curve distribution. –  jrista Oct 11 '10 at 4:25
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@jrista That's exactly what I said - shutter lifetime (i.e. 100k actuations) follows the normal distribution, failure rate (i.e. the probability the shutter will fail at X actuations) follows the bathtub curve. –  Matt Grum Oct 11 '10 at 8:05

What happens when 100k is reached (or whatever the actual lifespan is) - does the shutter fail in a way that damages the camera? Can it be repaired, or is it effectively the end of that camera body's life?

**When the shutter goes it can be replaced for around £130 or free if under warranty and that is going by what I paid in June when my 450D stopped working. It doesnt as far as I know do any damage,dont try and force the camera to work.

You get a basic error code and when my camera died it failed at the zoo and playback of last 10 photos were damaged. The camera made some rattle noises and clunks before it died.

Since being replaced it works like a dream, make sure to store your own personal setting as 10days plus without a camera and it being reset made my best companion a stranger.**

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It's not a big concern. (Most) All current new DSLRs have Shutter Actuations Life Prediction from 100,000 (Nikon D5100) to 400,000 (Nikon D4). Average it's about 150,000 to 200,000. Like a car, besides mileage and age, how long it last also relies on the owner care.

If the shutter ever stops working, send it to Nikon and, depending on model of your Nikon DSLR, the cost to replace a new shutter assembly is $119 and up. Stop worrying and just continue to fire the shutter. :)

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