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Old Jan 31, 2010, 2:47 PM   #21
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I'd like to clear something up.

We're not talking about "Average".

When the manufacturer rates a shutter at 100,000 actuations, there is a level of certainty to that number, probably 90%, maybe even 95%. That means that only 10%, possibly only 5% of the shutter mechanisms will fail before they reach 100,000 actuations. That's a lot better than "Average" which means that half of them will fail before 100,000.

The Mean (average) Cycles (in this case, shutter actuations) Between Failures (MCBF) is probably close to a million, and maybe even higher.
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Old Jan 31, 2010, 3:26 PM   #22
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Assuming you are correct that a shutter rated at 100k actuations means that 90% of cameras will reach that absolutely DOES NOT mean that MCBF is close to a million or more.

It is perfectly possible that 90% will reach 100k and only 1% or none at all will reach 1 million.

Think about it for a minute.
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Old Jan 31, 2010, 5:55 PM   #23
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Where the mean (the 50th percentile) lies with relation to the 90th percentile depends entirely on the distribution of the number of actuations until failure, and the manufaturers aren't publishing that data. But there's no reason to presume that the mean wouldn't be closer to 1,000,000 than to 100,000.
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Old Jan 31, 2010, 10:37 PM   #24
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Quote:
Originally Posted by TCav View Post
I'd like to clear something up.

We're not talking about "Average".

When the manufacturer rates a shutter at 100,000 actuations, there is a level of certainty to that number, probably 90%, maybe even 95%. That means that only 10%, possibly only 5% of the shutter mechanisms will fail before they reach 100,000 actuations. That's a lot better than "Average" which means that half of them will fail before 100,000.

The Mean (average) Cycles (in this case, shutter actuations) Between Failures (MCBF) is probably close to a million, and maybe even higher.
This is sort of what I was wondering when I asked the question. I knew there were published MCBF rates, but I wasnt sure if that was a fairly hard number, like around 100k you better start thinking about what you would do, or if it was just a way to gauge it's lifespan compared to other models. This answer cleared that up pretty well. Thanks as always.
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Old Feb 1, 2010, 7:00 AM   #25
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If 100,000 were the 50th percentile (the mean, or average) then a lot of shutters would fail at less than 70,000, and those people would all be ... very angry. And few if anyone would reach 200,000.

If 100,000 were the 90th percentile, or even the 95th percentile, the vast majority would get to 100,000. And most people probably would reach 200,000 and would be very pleased.

If you made cameras, which situation would you rather be in?
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Old Feb 1, 2010, 10:09 AM   #26
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Quote:
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... I knew there were published MCBF rates, ...
Actually, no. I think Seiko makes the shutter and mirror box assemblies (or components) for most camera manufacturers, and they don't publish the MCBF data to the general public.

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... but I wasnt sure if that was a fairly hard number, ...
That's a pretty hard number. They test the heck out of these things, and redesign failed components as required. They can test a batch of them, extrapolate reliability data from that, and make predictions about future reliability.

Predicting the future is easy; being right is tough. But they're doing everything they can.
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