The... horrible suspicion

[AlanF]

I've never had a problem with Canon lenses (except for a 50mm 1.8) but I recently bought a Tamron 85mm 1.8 and thought I got a dud.
I amfa'd it on a tripod and it still wasn't focussing correctly, then decided to amfa it hand held (as that's how it's going to be used), and after around 30 minutes of fiddling, it now focusses very well.

Sometimes you need to make adjustments in different ways to get a lens to play nicely.

You could get a steady job as a human tripod.

 

[GP.Masserano]

Many thanks for your answers.
Can you explain (In extreme synthesis) what is the 6 SIGMA QA process that you have mentioned in many topic?

 

[mackguyver]

Many thanks for your answers.
Can you explain (In extreme synthesis) what is the 6 SIGMA QA process that you have mentioned in many topic?

It's something I work in as well, and the simplest way to explain it is that you're targeting 99.99966% of whatever you make or do to be within specifications (i.e. not defective). That's 3.4 defects per million lenses (or bank transactions, email transmissions, etc.). The key is in have reliable ways to measure the product (lens in this case) is within specifications, detect when it is not, and better yet, engineering it up front so that the product is within specs 99.99966% of the time. Getting there is pretty complicated, but that's what the goal of Six Sigma is in essence.

One area where you will have noticed the impact of Six Sigma is in the thickness of aluminum cans and plastic water bottles. By engineering much better quality into the manufacturing, they have been able to reduce the specification (range of acceptable thicknesses) to the point where they can consistently make them near what used to be the lower limit (thinnest measurement of thickness). Thus, bottles are much thinner and by using less plastic while still having a strong enough bottle, they are saving millions each year. Too bad they don't pass on the savings, right?

For lenses, it means that whatever range of quality they have deemed acceptable for each lens can be manufactured more reliably and saving them money by having less lenses that don't meet spec and must be recycled/remanufactured. For us, that means that their newest lenses, no matter the price, are going to be more consistent than their older lenses, because those lines are still in use, but likely haven't been modernized with Six Sigma or other processes to improve quality/consistency. Lensrentals has noted that about the newer Canon lenses.

 

[C4userguy]

The Japanese do not use QC, but 6 Sigma QA which is much more demanding than QC. QC samples lenses off the production line, and verifies that "X" percent meet standards, usually 2-5% are allowed to be out of specification. That practice has long long ago been abandoned by Japanese manufacturers and most others major manufacturers.

Six Sigma processes inspect every lens. They are inspected by the assemblers at defined steps during manufacturing and assembly, and every finished lens is tested. There is variation, of course, tha'ts where the 6 Sigma name comes in.

" A six sigma process is one in which 99.99966% of all opportunities to produce some feature of a part are statistically expected to be free of defects (3.4 defective features per million opportunities). "

But ...assuming every lens leaves the factory perfect, how many would arrive in the same condition, considering the transportation process which is entirely out of Canon's hands.

There is no 6 Sigma in transportation, containers of products get banged around loading and unloading from ships, while being moved on trucks and trains, pallets get dropped by forklifts, then lenses are transferred to pallets in boxes for shipping to retailers, and get more rough handling. Within a large retailer, they can be subjected to dropping and spearing with forklifts, and then, from the retailer to the consumer, by UPS , FedEx, etc, they get extremely rough handling.

I believe that when a decentered lens is received, the odds are that it left the factory in perfect condition.

Have you noticed Roger Cicalas tear-downs of the newer "L" lenses, they are being built much more robust, I suspect that's mainly due to Canons recognition of the cost due to failures during shipping. The last new lens I bought (100-400mm L II) was packed much better than older lenses were, again a sign that Canon recognizes the problems during transportation.

And, of course, Roger has published articles about how many lenses of his are damaged in transportation. That's why they do a 100% inspection, yet, customers receive bad lenses.

I don't even know where to start with this post.

 

[AcutancePhotography]

I don't even know where to start with this post.

Then maybe you should give it some thought and decide what you want to write before you post a reply?

 

[Zeidora]

sigma = statistical standard deviation. 2 sigma (precisely 1.96 for larger number of observations, usually taken as >>100, but usually rounded to 2 for ease and good measure) is the 95% confidence interval. 6 sigmas is way further our on the bell curve. As Mt spokane pointed out, 99.99966% confidence interval. Haven't checked, but sounds about right.

Standard deviation = Square root of sum of squared deviations from mean divided by number of observations minus one.

hope that helps. If not, google standard deviation in statistics.