One point of failure vs many?

[Peter Rush]

A little off-topic but taking up Roger's point about camera failure - during the ceremony/speeches I have a CX730 slung around my neck so I can lock off my camera and get some cutaways, but it would also come into play if my main camera went down.

Pete

[Robert Benda]

Adrian, the correct probability is always the same. If a card fails one out of 1000 times, that will stay true.

Then, the chance that two of your cards will fail at the same time is 1/1000X1000, or 1 in 1,000,000.

Back to the original question, I like to use 32GB cards, and we switch them out as we move between the 3 main parts of the day: before, during, and after the ceremony. With 3 cameras of coverage, if one card failed, we're not completely and utterly screwed.

[Michael Silverman]

Roger, now I'm tempted to have a backup vehicle at all times in case my car dies!

[Roger Gunkel]

Originally Posted by Michael Silverman

Roger, now I'm tempted to have a backup vehicle at all times in case my car dies!

Hi Mike, Didn't mean to scare you :-)

Roger

[Adrian Tan]

Originally Posted by Robert Benda

Adrian, the correct probability is always the same.

Hey Robert, let me have one more go at persuading you, because this question bugs me! And if this attempt fails, I promise I'll stop annoying everyone and won’t say another word about probability (but will be happy to read anyone’s correction to my half-remembered maths).

I flip a coin twice. What are the possible combinations?

HH
HT
TT
TH

And they’re all equally likely, right?

Question 1: What is the chance that I flip no heads at all? Well, there’s only one combination out of four that has no heads. So the probability is 1/4, right?

Question 2: What is the chance that I flip at least one head? Well, you could work it out by counting how many combinations out of four contain at least one head (ie, three). Or you could say the probability is:

1 - (chance of no heads)
= 1 - 1/4
= 3/4

I then flip the coin a third time.

HHH
HHT
HTH
HTT
TTT
THT
TTH
THH

Question 3: What is the chance that you've got at least one head over the course of the previous three flips?

By similar reasoning, it’s 7/8 (I'm hoping you'll agree). 7/8 is larger than 3/4, so the upshot is that the more you flip, the higher the chance that you’ll have flipped at least one head. (Or: the more memory cards you use, the higher the chance that at least one will be faulty.)

I then flip the coin one more time.

Question 4: What is the chance that it’s a head?

Well, possible outcomes are:

H
T

and the number of combinations that contain a head is one.

So the chance is 1/2. All the previous flips don’t affect the next flip.

Incidentally, if one really wanted to think like a robot, it's actually possible to go a step further beyond probability and apply "decision theory". To cut a long story short, I think the four-card choice vs the one-card choice, on decision theory, is the rational choice. Won't bore everyone with the explanation.

[Robert Benda]

Originally Posted by Adrian Tan

So the chance is 1/2. All the previous flips don’t affect the next flip.

Correct, though there is always the regression to the mean. If you flip you start flipping your coin, maybe you start with 8 'heads' in a row, which is statistically unlikely, but possible. The longer you flip the coin, the more likely it will regress back to the mean, or 50% heads and tails. Of course, every individual toss is still a 50% chance of heads or tails.
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Our problem, of course, is that we're talking about our gear. We have no idea what the actual failure rate is for our memory cards, and the longer we use them, the higher that failure rate likely is. It doesn't mean its likely to fail, though, from a math point of view.

From a practical point of view, none of us take that chance, though. I'm sure we'd all say that, the day you're not prepared is the day something will break or fail for you.

We just all have to balance convenience to safety. I like 32GB cards and start fresh for the ceremony, then new cards once its over, etc. That's not really my safety measure. Running 3 cameras is (and I'll move to 4 soon). This protects me both from equipment failure, and from bad situations, like obstructed views. Same reason most of us use more than one audio recording method.

[Chris Harding]

Hey Adrian

OK so the bottom line is that you need a backup for everything ...spare car, spare clothes, spare cameras, batteries, tripods, lights, and the list just goes on and on.

I think this really comes down to being practical surely?? Carry spare cards and batteries with you but don't become obsessive about failing gear ... The likelihood of it happening is very remote so rather enjoy filming your weddings and let the gear look after itself

Chris

[Dave Blackhurst]

Dice don't have any mean time between failure...

Because electronics DO, there should always be a clause in the contract/retainer limiting exposure to the original amount paid (for a full catastrophe, or loss/theft), or a part thereof, should there be an "equipment malfunction".

While any piece of electronics CAN fail, generally if it works initially (burn in or a few usage cycles), it will work for quite some time if not subject to abuse (liqiud, impact, crushing). This is presuming that you're not buying fakes/knockoffs or substandard quality products.

It's quite likely that decent quality cards will become unusable due to a requirement for larger file sizes or faster speeds before they "wear out" due to read/write cycles... my 8G cards are still working just fine, but when shooting XAVCS, 64 and 128G are the rule...

[Roger Gunkel]

Dave is absolutely right, rather than failing, cards etc tend to become obsolete as the technology progresses.

Another point is that card failure is more likely to be as a result of mishandling or placing somewhere where there is a high electro/magnetic risk. If a card is working fine in my camera at the start of the day, it is unlikely to suddenly fail. There is a remote chance of failure on removal by damage to the contacts, so the footage could be downloaded before removal to prevent that possibility.

I also like to make sure that the performance requirement of the camera doesn't exceed the performance of the card, to avoid glitches and lockups etc.

Roger

[Dave Blackhurst]

And I'd point out that there have been "found" cards that were lost by their owners when the cam went overboard or down a crevasse or into a mudslide... and the images were recoverable.

Generally speaking, short of destruction, or an EMP, cards tend to be fairly reliable - some manufacturers do list use cycles or such that can give you some idea of "potential" failure rates, and I really suspect if a card is "good" through a couple write/read cycles, it's probably good for more than most of us will ever shoot before it's obsolete and no longer big enough or fast enough to hold our files...

[Kyle Root]

This kind of thing has always been a concern and now that I'm charging much more than I did years ago... the thought of a failure is always at the front of my mind when setting up.

This is why I shoot all wedding ceremonies with 4 or 5 cameras and individual audio recorders with wireless and wired mics going to my main cam and DR40.

As far as cards go, that's what I love about the Sony NX5. I get an instant backup to the FMU128 in real time.