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A good lens sample?
Posted By: pacerr, 09-17-2012, 10:11 PM

QuoteQuote:
Was I was lucky and Providence picked a good lens sample [ -- or am I gonna have to return this one too ] ??
Here's an admittedly over-simplified look at manufacturing QA in general that may be useful. A sort of histogram for QA.

For the sake of discussion let's note some typical considerations for a DA-kit lens vs. a Star* or Limited quality lens.



Note 1 - Regardless of type or cost there'll always be a few random, defective items that for some reason escape notice in the QA screening process and make it into the market place. Higher cost items have a higher QA sampling rate as part of the inherent price tag. A 100-percent QA screening rate and life time guarantee can be extremely expensive, but possible.

Note 2 - depending on things like the quality of the design and materials, age of the tooling, experience of the work force and quality control measures the chance of getting a better or worse example of the lens may be spread over a wide bell curve or may be concentrated near the high (or low!) end of the curve.

Note 3 - the chances of getting a best quality lens is much greater of course as more expense is put into the manufacturing process. Random events will ensure there will still be less-good lenses to the left side of the distribution curve - just fewer of them.

Note 4 - but the interesting thing is there's still a chance that random events will produce a serendipitous winner on the far right side of the curve with even the lowest cost lens - within the constraints of the less expensive materials of course. You may have to search through a LOT more low-cost lenses to find that hidden 1 in 10,000 gem though.

I had an example of that a few years ago. I was fortunate enough to have three DA 50-200s in hand at the same time for side-by-side comparison and time enough to explore them. Two of them produced so-so, middle of the curve results as expected. The third one however was a real stand-out in image quality despite having a flaw in the lettering on the aperture ring. Those that can only experience a single sample of a given lens can only go by reviews and prior personal experience in judging that lens.

When a new product comes out or there's a disruption in the materials, manufacturing or QA process there'll be more random events to the left side of the curve unless extraordinary effort and expense is made to weed out the anomalies until normal activity returns.

A basic understanding of manufacturing processes and QA sampling helps reduce the frustration of finding gear you're satisfied with. Ultimately, you really do get what you pay for, but sometimes you just might get lucky anyway.

H2

Last edited by pacerr; 09-18-2012 at 09:00 AM.
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09-18-2012, 02:52 AM   #2
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Good point. And to your statement, "Ultimately, you really do get what you pay for", you might consider adding a third curve showing cost vs. quality because, it isn't just linear (unfortunately).
09-18-2012, 09:12 AM   #3
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QuoteOriginally posted by Stone G. Quote
because, it isn't just linear (unfortunately)
True, but I'll leave that graph to someone else. I'm already sort'a out of my league just offering a stat curve.

I'd note that one factor in the non-linear connection you mention is that regardless of the expense that goes into any given product, only a fraction of its cost is directly related to its intrinsic quality. There are other fixed costs like transportation, marketing, facilities maintenance, employee benefits, etc that aren't related to the quality of a specific item but contribute to the overall cost. Oh, an' don't forget enough profit to want to remain in business.

H2

Last edited by pacerr; 09-18-2012 at 10:39 AM.
09-18-2012, 11:06 AM   #4
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QuoteOriginally posted by Stone G. Quote
Good point. And to your statement, "Ultimately, you really do get what you pay for",........
I think the statement must be modified to emphasize the stochastic nature of the beast. In aggregate we collectively get what we pay for, but may individually get better (or worse) than we paid for.

Dave in Iowa

09-18-2012, 06:47 PM   #5
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While it would be nice if you got what you paid for, in reality there seems to be an inordinate amount of suboptimal DA* 55/1.4 (decentering) and FA 31/1.8 (lens barrel wobbles with a negative impact on IQ) copies, to name just two examples.

Hence I reckon your graphs are just conjecture rather than being based in reality. Or do you have access to any real data?
09-18-2012, 10:19 PM - 1 Like   #6
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QuoteQuote:
what about the older lenses that have been around for a long while?
I believe those that haven't been relegated to the trash all eventually end up on a shelf.

Those that were "born" on the right side of the performance graph are valued friends proudly displayed and ready still for work or play.

Those from the left side of the graph get passed around to hopeful LBA-ers by unscrupulous sellers until they end up in the hands of an ethical photographer who gives them a respectful retirement. In a moment of compassion, one may make space for 'em on the shelf next to their more gifted brethren -- a sort of Old Lens Home at Fiddler's Green.

(Yeah, okay, so there's a tot o' rum with a pipe an' tobacco for 'em on the shelf here. Maybe that explains why there's so damn many of 'em hanging around here anyway! )

I'd guess that as a given type of lens ages and its total numbers dwindle owing to misadventure, the bell curve tends to shift to the right as the poorer performing individuals get culled from the remaining active population. The cautionary situation here is finding a poor performer that was put away years ago and is being sold today in "like new" condition. A "gently" used older lens is a good indication it was a "good" lens, one from the right side of the curve. A seller's reputation is your best guide there.


[And before you ask about Fiddler's Green, in folklore it's an idealized afterlife for us old sailors where there's always rum and tobacco, the fiddler plays 'til dawn and the barmaids are all buxom beauties . . . sort of like Hooter's would've been before the invention of TV!

In the lyrics of an ancient mariner's song:

At Fiddler’s Green, for seamen true
When lo they’ve done their duty,
The pipe and bowl shall quick renew
And pledge to love and beauty.

That's not a bad retirement for a favorite old lens either, when 'lo it's done its duty'.

H2

Last edited by pacerr; 09-19-2012 at 09:53 AM.
09-18-2012, 10:52 PM   #7
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QuoteOriginally posted by Class A Quote
Hence I reckon your graphs are just conjecture rather than being based in reality. Or do you have access to any real data?
QuoteQuote:
. . . an admittedly over-simplified look . . .
The original question was, did I get lucky? The answer: maybe so and it might happen this way. How lucky? How much did you pay?

There's certainly a difference between a flawed design or assembly/QA process and the general nature of "quality" distribution for a mature product. Either the market place will cull the poor designs and processes or the manufacturer will correct the errors within the limitations of the profit margin of the product.

Note: Somewhere in the history of every unsatisfactory product, there's a pissed off design-engineer that fought the bean-counters over a process and/or design that couldn't be sold at a marketable, business-sustaining price.

H2
09-20-2012, 10:48 AM   #8
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a couple of points to highlight here, which I think people over or under estimate as a function of perspective.

There are numerous studies that show 100% inspection is only capable of capturing 80% of the defects. DOnt believe this, get a group of friends, and with a 1 minute time limit count the number of occurrances of the letter E on a page in a magazine. compare notes, then carefully count them all. The point of this is that inspection is NOT the way to achieve quality, it is a stop gap measure at best, or more importantly a means to either reject entire batches of something, or to be used as a means to "tweek" operating processes.d

To make real sustainable improvements in product quality requires Process not inspection.

design also plays a part, the comment about having one stellar example in 3 indicates the difference between ideal and non ideal limits of the assembly as considered by design. This gets you into the whole realm of the production tolerances and the impact on performance. From a purely engineering point of view, if the requirements can be met with very wide tolerances, that is (for me) the best design. That is what every designer should be aiming for, because the tighter the tolerances, the more expensive it is to make, but the tighter tolerances and additional cost do not necessairly directly imply a better IQ or even a better lens.

09-20-2012, 12:07 PM   #9
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Good points.

The "perfect" design would anticipate and avoid ALL potential faults
and failure modes and therefore require no QA screening processes.

Possible? Perhaps, but not probable in execution.

Remember, Murphy is alive and doin' well an' he breeds
often and promiscuously -- especially after 'last call'.

H2
09-21-2012, 10:53 AM   #10
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in a perfect world, teh design and assembly process should be such that no fancy tools are needed and no quality system is required, however, in order to reduce costs, waste , materials etc. the engineers come up with all sorts of bright ideas, and tricky designs that are a real bear to manufacture and maintain.

A great example of this is the Panzer tank, compared to the Shermin tank. Sure the Panzers were better performing, but the shermins were much easier to repair and manufacture, and with things like tanks, you expect them to take damage therefore simplicity of design and industrialization is everything. at least it won WW II
06-16-2013, 02:08 PM   #11
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Interesting and somewhat surprising that there is such a variation in consistency between kit lenses and limited lens.
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