Archived posting to the Leica Users Group, 1997/06/11

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From: Otto Braasch <otto.braasch@bnla.baynet.de>
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Eng-Suan wrote:

>>>
You are correct to quote the MRBF of 322.6 rolls for your 4 bodies. What
I meant was if you take ANY RTS III randomly and use it *under the same
coditions* as you used for your 4 bodies, then the MRBF will be some
what more conservative. My calculation suggests it is at least 222
rolls. (based on one-sided Chi-square distribution at 95% confidence
level.)
  
If I have the data for R8 I could use what the reliability engineer
called time-truncated (without failure) to estimate the MRBF. But for
the two sets of data to have any meaningful comparison, the cameras must
worked under the same condition (the way you handled them and  the
environment they were subjected to.) 
 
And so far we are assuming the failure rates of the cameras are
constant, that is to say the MRBF of first 2 years is the same as that
of the subsequent 2 years. It is theoretically acceptable to consider
electronic circuits and equipment to have constant failure rate, but
rarely so for mechanical parts. You have been using RTS III for 3.25
years but the R8's are less that a year in the market....the
discrepancies are there.
<<<
 
Eng-Suan,

Thank you very much for commenting on the MRBF approach.

The objective I had in mind when posting the figures was to encourage 
other users to come up with their data - if they have any. Once users of 
Leica-R models post their figures, there might be some chance for a ROUGH 
comparison of body endurance between different R-models and other camera 
brands. Unfortunately photo magazines (for multiple reasons?) do not run 
any tests on durability of cameras, which, when done professionally under 
the same conditions, could supply users reasonable information.

I am fully aware of the many variables that will prevent a professional 
comparison when data are collected by different people under various 
conditions at different times. However at present it seems to be the only 
way to get rid of pure guesswork and hearsay when it comes to the 
question: "how long can I expect this camera to function under what 
conditions"?

Wonder, when we will see new MRBF figures here?

Regards,

Otto