Pentax Quality Control Strikes Again

Started Apr 23, 2015 | Discussions
Dukhat
Dukhat Veteran Member • Posts: 3,810
Re: Pentax Quality Control Strikes Again

Joseph Tainter wrote:

Gosman wrote:

How do you test for as decentered lens?

Photograph a brick wall with the camera on a tripod. As others pointed out, the camera body must be parallel to the wall. Shoot wide open. For a zoom lens, test across the focal length range. View images onscreen at 100%. Inspect edges and corners for unbalanced weaknesses.

Joe

Joe, are you taking field curvature into account? I'm presuming yes, you seem like one of the more knowledgeable people floating around out there.

OP Joseph Tainter Forum Pro • Posts: 10,996
Follow-up
1

I leave for Stockholm on May 2 and had hoped to give the DA 16-85 a workout. I am disappointed at not being able to. Instead I will take my DA 20-40 Limited, which has been a fine performer, although I wish it had more at the long end.

I have many lenses, mostly by Pentax. I have Pentax lenses from 10 to 600 mm, and most of everything in between. The majority of them have not had problems. So why do I test lenses? Here's why:

DA* 50-135:

My first copy arrived with a lens element loose and rattling around inside. Pentax used to individually inspect every * lens. Clearly they no longer do so. Pentax replaced it.

Second copy: I was in Rome. It worked fine. At the end of one day I put it to rest in my camera bag. The next day I took it out and it wouldn't focus. SDM dead. Pentax replaced it.

Third copy: It has been okay so far, but I haven't used it in a while. Letting an SDM lens sit around is apparently a primary cause of SDM failure.

DA* 16-50:

Copy 1: Optical decentering. Pentax replaced it.

Copy 2: Even worse optical decentering. I was busy and didn't have time to test the lens. As a result, I have many ruined photos from what will probably be my only trip to China. Pentax replaced it.

Copy 3: Slight decentering, but withing acceptable limits. SDM failed, and I paid to replace that.

DA 55-300:

Copy 1: Severe optical decentering at 150 to 170 mm.

Copy 2: Severe optical decentering.

Copy 3: Okay (I think).

DA 16-85:

Copy 1: Severe optical decentering.

Copy 2: I'll know in a couple of weeks.

I do much of my photography when traveling overseas. I have had photos from Italy, China, Sweden, and Tunisia ruined by faulty Pentax gear. I no longer take SDM lenses on these travels because I don't trust them.

Joe

OP Joseph Tainter Forum Pro • Posts: 10,996
Re: Pentax Quality Control Strikes Again
4

Dukhat wrote:

Joseph Tainter wrote:

Gosman wrote:

How do you test for as decentered lens?

Photograph a brick wall with the camera on a tripod. As others pointed out, the camera body must be parallel to the wall. Shoot wide open. For a zoom lens, test across the focal length range. View images onscreen at 100%. Inspect edges and corners for unbalanced weaknesses.

Joe

Joe, are you taking field curvature into account? I'm presuming yes, you seem like one of the more knowledgeable people floating around out there.

Field curvature doesn't matter. I check carefully for side vs. side, top vs. bottom, corners vs. corners for unbalanced weakness. It is lack of symmetry in weakness that tells that one has a lens with optical decentering.

Joe

DAVID MANZE Veteran Member • Posts: 5,767
Re: Pentax Quality Control Strikes Again
3

Joseph Tainter wrote:

Thanks, Dave.

Joe

I know your right Joe, there's no doubt in my mind, I have had a never never ending amount of de-centered lenses, the latest of which is the Tamron 150-600mm VC USD of which I am waiting for a replacement. I don't post about it much because I know the responses I will get from people who haven't seen the problems telling you how you've got it wrong, how your testing methods are awry etc., I just quietly return the lenses.

It's a shame we cannot be sympathetic towards those with woes, but it seems if you bring faults to light, it offends supporters of the brand who want to live in "no problems brand heaven"!

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MJSfoto1956 Contributing Member • Posts: 560
Re: Pentax Quality Control Strikes Again
1

Gosman wrote:

How do you test for as decentered lens?

The best/easiest way is to point the camera/lens at a dark sky star field and manually focus on a star in the center using live view. Take a picture (at high ISO if necessary) and then examine all the stars, particularly in the corners. If one corner or side is soft then the lens is decentered.

Michael

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awaldram
awaldram Forum Pro • Posts: 13,270
Re: Pentax Quality Control Strikes Again

DAVID MANZE wrote:

awaldram wrote:

Joseph Tainter wrote:

I just got a DA 16-85. As with any new Pentax lens, I immediately took it out for a brick wall test. Sure enough, it is optically decentered, with bad weakness on the right side.

That's my second bad Pentax lens (out of two new lenses purchased) since last summer.

It's going back.

Joe

I think Joe your version of acceptable is not the same as Pentax's , This isn't meant as a criticism just a fact.

No it's just bl....dy unsympathetic!

Rubish I would assume English isn't your first language only it is so your obviously driving an agenda !!!

I assume Pentax and all manufacturers assess what passes most peoples casual usage and doesn't generate returns when they set the pas/fail limit for quality control (not sure if there is any legal definition)

This obviously true else penta. Would go bust it everyone returned lens at the same rate Joe has to , Unless your of the opinion Joe is the unluckiespentaxian in the world

As all lens are decenterd it much more likely Joe tolerance is less than the average. Just as my tolerance for CA is lower than average.

Given the large number of failures you get I can only assume your more discerning than the average user and hence your only option is personally test and fail lens as you get them.

On the plus side its good that Pentax accept your version of 'faulty' and don't return them as no fault found.

We used to have a similar issue when TFT lcd's first became affordable users would try and return units for one dead pixel and seemed put out that this was 'acceptable' and within European giudlines as serviceable and as such woudl not be accepted for warranty repair/replacement.

This wasn't meanness on the part of the manufacturers but purely if we replaced a 1 dead pixel unit they'd possible get more dead, our QC limit was 5 where European (legal definition of serviceable ) guideline was 20 at the time.

What is your game Andrew?

Joe has bought yet another lens that is decentered and you make out that it is his ridiculous standards that are at fault and not the fault of Pentax. Do you not think that Pentax know damned well when a lens is out of kilter? If it wasn't the case why would they be using pixel shifting technology, so they can make the most out of decentered lenses?

Your good at the straw man. Otherwise known lying !! I did not imply or even think Joe's standardised are ridiculous.

So please stop lying in your effort to drive some pro penta. Fanboy crxp

Then we get "how generous Pentax are for accepting his opinion of the lens", as you know I know a guy at Pentax and his opinion is "absolutely not yours", as far as he is concerned de-centered means the lens has a problem and as such it should be replaced and as such will replace it!

I'm beginning to think your a little foolish in your personal attacks as well as boring

All lens are so who's the idiot you know who thinks every lens made has a problem ? Or are you again lying !

"Please be a bit sympathetic towards other peoples woes" when they are buying de-centered/faulty lenses at several hundred euros a pop.

My post was supportive showing I trusted and approved of Joe's testing and stance  , it is your warped mind which sees what's not written driven by your own crazed at end where you take very opportunity to snipe at me petty small minded if you ask. Me !!

Good luck Joe!

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Petroglyph
Petroglyph Veteran Member • Posts: 6,089
Re: Follow-up

I sent back my first copy of 60-250 because the box had clearly been smashed during delivery.  I thought I heard the 'squeak of death' from the lens motor and saw a lot more PF than I expected in my first test shots.  Second copy has been brilliant with no issues.

As for QA you have to run your own these days.

I sent back a Nikkor 24-85 for various reasons once upon a time, including it was leaking lubricant back onto the rear element.

Generally, though I've had pretty decent luck with all brands I've tried and the occasional clunker has been returned.

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McSpin Contributing Member • Posts: 502
Re: Pentax Quality Control Strikes Again

Joseph Tainter wrote:

Dukhat wrote:

Joseph Tainter wrote:

Gosman wrote:

How do you test for as decentered lens?

Photograph a brick wall with the camera on a tripod. As others pointed out, the camera body must be parallel to the wall. Shoot wide open. For a zoom lens, test across the focal length range. View images onscreen at 100%. Inspect edges and corners for unbalanced weaknesses.

Joe

Joe, are you taking field curvature into account? I'm presuming yes, you seem like one of the more knowledgeable people floating around out there.

Field curvature doesn't matter. I check carefully for side vs. side, top vs. bottom, corners vs. corners for unbalanced weakness. It is lack of symmetry in weakness that tells that one has a lens with optical decentering.

Joe

Could you define "unbalanced weakness"? I have no idea what that means and I'd like to check my lenses.

candgpics Regular Member • Posts: 143
Re: Shipping?

Hi. I often order lenses from Amazon.com. I wonder how much Amazon's packing and UPS' shipping--or whichever retalier and shipper was used--affect such failures. My first Sigma 70-200 was doa (would not focus at all). Sigma tech support suggested I return it to the retailer for a replacement, which I did.

Having said the above, I have had two sdm failures on the16-50 and one sdm failure on my 60-250. Plus, my first k5 would not focus with any of my lenses and the next had quite visible oil spots at f8. Also, a k5ii needed to be replaced due to a faulty mirror box.

So, I am not unsympathetic. I hope you get a good copy. I have become interested in this lens after initially dismissing it.

I am hoping Pentax will run a rebate when the k3ii is released.

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OP Joseph Tainter Forum Pro • Posts: 10,996
Re: Pentax Quality Control Strikes Again

McSpin wrote:

Could you define "unbalanced weakness"? I have no idea what that means and I'd like to check my lenses.

Check the procedure here:

http://www.dpreview.com/forums/post/55705482

Edges and corners are always softer than the center, especially wide open (largest aperture). Check whether sides, top/bottom, corners have equal softness, or if one side or corner is weaker and the others.

Joe

Timbukto Veteran Member • Posts: 4,988
Re: Pentax Quality Control Strikes Again
5

Joseph Tainter wrote:

Timbukto wrote:

I would suggest you do MFA tuning prior to brick wall tests. This is because if the lens is front focusing, it is possible that due to field curvature, some portions are within sharper focus than others. No lens in existence exhibits absolute perfect flat plane field curvature, but by not calibrating it first you may be seeing the tail end of your field of focus instead of the middle portion, etc.

Likewise my 18-55 by default looks to have soft portions in some areas and not others, but with MFA tuned, it can give me a sharp frame to frame 18mm f3.5 shot.

See here -

http://www.lensrentals.com/blog/2015/03/a-quick-zoom-variation-demonstration

Thanks for the recommendation, but this wouldn't account for unbalanced weakness. That can only come from defective assembly.

I've done this test on many lenses before testing for focus compensation. Nearly all have subsequently needed some degree of focus compensation adjustment.

Joe

It is not a black and white issue. Slight imbalance does not matter and can be exacerbated by not having the lens focus calibrated.

Lets pretend that the field curvature of a lens is like a rainbow...a double rainbow even. Lets pretend the area between a double rainbow is what is in focus. Now lets assume the rainbow is not a *perfectly* concentric cone and there is a slight tilt, but there is a good deal of space in the *middle* portion of the double rainbow. Can you see how back focus and front focus can thus exhibit *uneven* softness in the frame?

Like I said read Roger's article...no lenses are *perfect* at all focal lengths. But you *do* need to make sure your focus is dead on so that you are putting as much as possible in field of focus. My 18-55 clearly has the right side coming into focus slightly after the rest of the frame. I can consider it defective, or I can just make sure the focus is spot on and adjust it for rather good quality at 18mm f3.5.

Case in point...this is an image with the kit lens that looks like the upper right area is a soft blob.

Same lens...corrected focus...sharp all over on a kit lens...hurray for me. An f3.5 shot beating a stopped down f5.6 shot. This is how a lens transforms from junk to pretty damn good.

I've been across many brands and many lenses, preowned and new. I have more thoughts on the matter but my findings are like Rogers...a ton of lenses are imperfect especially zooms. Better is the enemy of good enough is the line he uses...that is exactly why I've gone all over the place from full frame L lenses to a Pentax with a double kit lens.

Overall thoughts on quality vs brands -

It is *largely* no big difference but there are some factors to consider.  IMO Full frame or larger systems have an advantage compared to APS-C and smaller systems in what I consider focal plane tolerance.  Overall it is more difficult to make lenses of wider focal lengths with perfect field flat field curvature with no tilt.  However systems of larger sensors make equivalent focal lengths provide wider AOVs.

In otherwords it *tends* to be the case that it is easier to make a sharp 85mm 1.8 than it is to make a sharp 50mm 1.8.  It is easier to make a sharp 50mm 1.8 than it is to make a 35mm 1.8.  So in otherwords larger sensor systems gain an advantage in terms of optical quality for the same AOV.  Keep in mind that it tends to be that Pentax has been criticized for optics but they have long been only APS-C.  Sony E-mount prior to any full-frame mount has largely been criticized for lens optics as well and deservedly so in some instances.

Very few *full-frame* systems and lens mounts invite as much criticism IMO because in general it is *easier* to build optics for because it tends to be that tele designs are inherently easier to make sharper(yes tele's can still be large and hideously expensive, but overall they provide the sharpest results compared to wide angles).

I've had hit and misses across brands and systems, but I do tend to believe its easier to make a sharper 85 than 50, and 50 than 35, etc.

I also believe that when people spec lenses for smaller sensor mount, they try to maximize sharpness for what is essentially far tighter pixel pitch, but for size reasons also under-engineer edges (to suit APS-C size vs FF size).  So in general many FF lenses aren't necessarily as sharp, but many should provide uniformity.  In addition because the 'peak' sharpness of FF lenses might not even be as high as the peak sharpness of an APS-C designed lens, instances of non-uniformity stand out much greater.  Sony e-mount lenses are designed to be small as possible exactly for APS-C...they have the SAME complaints in satisfying 24MP sensor.  Centers are sharp...borders and edges not close...and uniformity not that great.  IMO Pentax seems to have similar constraints (i.e. the 50-200 tele I have is very very compact...and brighter than the Sony one to boot).  Although IMO my double-kit lenses are better than the Sony's 16-50 and 55-210 double kit.  MFT often gets a pass but IMO the sensor size aspect ratio tends to make for easier to build optics...but even then I've had terrible times finding a good copy of a Oly 45mm 1.8.  Also mirrorless cameras can have terrible times getting everything in focus at infinity at times because many hybrid AF heuristics optimize on speed and the moment the *FOCUS* point in question is sharp that is where it is focused on...but like my image example shows there may be more careful focusing that gives better results.

Overall because Pentax has both focus peaking, catch focus, and focus tuning...it is one of the *best* brands to optimize IQ for at the entry level.

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soheil Veteran Member • Posts: 3,024
Re: Pentax Quality Control Strikes Again
1

Joseph Tainter wrote:

McSpin wrote:

Could you define "unbalanced weakness"? I have no idea what that means and I'd like to check my lenses.

Check the procedure here:

http://www.dpreview.com/forums/post/55705482

Edges and corners are always softer than the center, especially wide open (largest aperture). Check whether sides, top/bottom, corners have equal softness, or if one side or corner is weaker and the others.

Joe

Joe,

I'm sure you know this already butI'd like to remind you to do your test both in landscape and portrait modes and see if you get the same result at the same corner. This way you'll be sure if your setup is accurate or not.

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------------------------------
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DAVID MANZE Veteran Member • Posts: 5,767
Re: Pentax Quality Control Strikes Again
1

awaldram wrote:

DAVID MANZE wrote:

awaldram wrote:

Joseph Tainter wrote:

I just got a DA 16-85. As with any new Pentax lens, I immediately took it out for a brick wall test. Sure enough, it is optically decentered, with bad weakness on the right side.

That's my second bad Pentax lens (out of two new lenses purchased) since last summer.

It's going back.

Joe

I think Joe your version of acceptable is not the same as Pentax's , This isn't meant as a criticism just a fact.

Joe's lens was not tested optically........they don't check every lens optically just an occasional sample! . there's just a quick mechanical check.

...........so it comes off the line and goes into the box ...

So how would Pentax have known whether it was good or not?......

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Jim King
Jim King Veteran Member • Posts: 8,560
Re: Follow-up
2

Joe, like you, I have had my issues with various Pentax lenses over the years. Most of the time I have been able to adjust focusing to get acceptable if not stellar performance. But I am confident that your problems are real, not imagined or the result of flawed testing. That said, you seem to have had a worse run of bad luck with your Pentax lenses than most of us. That's very unfortunate.

Because I can't fully trust Pentax to get their lenses right I've been using Fuji X gear more of the time in the last several years. Fuji X lenses, while still not perfect, seem somewhat better than the average Pentax lenses I have owned (and that is most of them, as you know). Of course, CDF helps avoid the focusing errors of CDAF. Perhaps you should look outside the Pentax fold...

I still keep a Pentax kit and probably always will - after all, I've been a Pentaxian for over 50 years. There is much to love about Pentax photo gear. But sometimes you have to do what you have to do.

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Pentaxian for over 50 years.
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awaldram
awaldram Forum Pro • Posts: 13,270
Re: Pentax Quality Control Strikes Again
1

DAVID MANZE wrote:

awaldram wrote:

DAVID MANZE wrote:

awaldram wrote:

Joseph Tainter wrote:

I just got a DA 16-85. As with any new Pentax lens, I immediately took it out for a brick wall test. Sure enough, it is optically decentered, with bad weakness on the right side.

That's my second bad Pentax lens (out of two new lenses purchased) since last summer.

It's going back.

Joe

I think Joe your version of acceptable is not the same as Pentax's , This isn't meant as a criticism just a fact.

Joe's lens was not tested optically........they don't check every lens optically just an occasional sample! . there's just a quick mechanical check.

...........so it comes off the line and goes into the box ...

So how would Pentax have known whether it was good or not?......

You perhaps are not aware how manufacturing works in the modern age

The only reason 'occasional' lens are checked is to ensure the lens are coming off the manufacturing line within 'acceptable defined limits. It has nothing todo with checking the lens itself (it doesn’t get a 'checked' stamp)

Manufacturing plants use designs and build technique to achieve a set quality .... they then randomly check the plant is hitting that quality.

This doesn't mean things can't go wrong but is unlikely and even it it does not for an appreciable run before detected.

The company I work for has a 2% limit for failing memory simms , One of the manufacturers we 'badge' has a 5% limit consequently we QC every simm from this manufacturer so that we can deliver on our 'promise' with our label.

The same applies to Joe even though it's manufacturer to user, Pentax obviously have a lower standard than Joe therefore the only way Joe can be sure to get 'what he requires' is to test every lens he buys, As his standard is greater than the manufacturers a good proportion will fail his test.

This is because as designed they were never meant to pass his test hence he needs the better ones off the production run rather than average.

Pentax on the other hand couldn't care less they set their 'standards' to keep returns and warranty repairs to an acceptable level and if they can put two milk bottoms on a pepsi can and sell it for £1000 with low return they will.

To assume otherwise shows a level of brand blindness that is the true 'fanboy state' to believe Pentax make lens as a service to their users rather than make money !!! and leads to the disillusioned rants we often see in these forums ..... hell has no fury like pentaxian  spurned

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Jim King
Jim King Veteran Member • Posts: 8,560
Re: Pentax Quality Control Strikes Again

awaldram wrote:

You perhaps are not aware how manufacturing works in the modern age

The only reason 'occasional' lens are checked is to ensure the lens are coming off the manufacturing line within 'acceptable defined limits. It has nothing todo with checking the lens itself (it doesn’t get a 'checked' stamp)

Manufacturing plants use designs and build technique to achieve a set quality .... they then randomly check the plant is hitting that quality.

This doesn't mean things can't go wrong but is unlikely and even it it does not for an appreciable run before detected.

The company I work for has a 2% limit for failing memory simms , One of the manufacturers we 'badge' has a 5% limit consequently we QC every simm from this manufacturer so that we can deliver on our 'promise' with our label.

The same applies to Joe even though it's manufacturer to user, Pentax obviously have a lower standard than Joe therefore the only way Joe can be sure to get 'what he requires' is to test every lens he buys, As his standard is greater than the manufacturers a good proportion will fail his test.

This is because as designed they were never meant to pass his test hence he needs the better ones off the production run rather than average.

Pentax on the other hand couldn't care less they set their 'standards' to keep returns and warranty repairs to an acceptable level and if they can put two milk bottoms on a pepsi can and sell it for £1000 with low return they will.

To assume otherwise shows a level of brand blindness that is the true 'fanboy state' to believe Pentax make lens as a service to their users rather than make money !!! and leads to the disillusioned rants we often see in these forums ..... hell has no fury like pentaxian spurned

Andrew, wouldn't you expect to something close to a standard distribution of "quality" around the center point of the design spec, with outliers and and beyond the edges of the spec?  if so, even if Joe's acceptance criteria are higher than Pentax's limits, I would think that he would still see a good proportion of acceptable lenses, with a few outliers.  Instead, most of the lenses he gets seem to be unacceptable to him.  Either his standards are absurdly high (and I don't think this is the case), his testing methodology is faulty, or he has had an extreme run of bad luck...

Your thoughts?

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Jim King - Retired Colormonger - Suburban Detroit, Michigan, USA; GMT -4h (EDT)
Pentaxian for over 50 years.
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- Sir Winston Churchill
* * * * *
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- George Santayana
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awaldram
awaldram Forum Pro • Posts: 13,270
Re: Pentax Quality Control Strikes Again

Jim King wrote:

awaldram wrote:

You perhaps are not aware how manufacturing works in the modern age

The only reason 'occasional' lens are checked is to ensure the lens are coming off the manufacturing line within 'acceptable defined limits. It has nothing todo with checking the lens itself (it doesn’t get a 'checked' stamp)

Manufacturing plants use designs and build technique to achieve a set quality .... they then randomly check the plant is hitting that quality.

This doesn't mean things can't go wrong but is unlikely and even it it does not for an appreciable run before detected.

The company I work for has a 2% limit for failing memory simms , One of the manufacturers we 'badge' has a 5% limit consequently we QC every simm from this manufacturer so that we can deliver on our 'promise' with our label.

The same applies to Joe even though it's manufacturer to user, Pentax obviously have a lower standard than Joe therefore the only way Joe can be sure to get 'what he requires' is to test every lens he buys, As his standard is greater than the manufacturers a good proportion will fail his test.

This is because as designed they were never meant to pass his test hence he needs the better ones off the production run rather than average.

Pentax on the other hand couldn't care less they set their 'standards' to keep returns and warranty repairs to an acceptable level and if they can put two milk bottoms on a pepsi can and sell it for £1000 with low return they will.

To assume otherwise shows a level of brand blindness that is the true 'fanboy state' to believe Pentax make lens as a service to their users rather than make money !!! and leads to the disillusioned rants we often see in these forums ..... hell has no fury like pentaxian spurned

Andrew, wouldn't you expect to something close to a standard distribution of "quality" around the center point of the design spec, with outliers and and beyond the edges of the spec? if so, even if Joe's acceptance criteria are higher than Pentax's limits, I would think that he would still see a good proportion of acceptable lenses, with a few outliers. Instead, most of the lenses he gets seem to be unacceptable to him. Either his standards are absurdly high (and I don't think this is the case), his testing methodology is faulty, or he has had an extreme run of bad luck...

Your thoughts?

I would agree and honestly don't know why Joe suffers such high failures.

I trust Joes testing so when he says a lens is d-centered I'm confident it is (at a level that easily users see-able)

Also the SDM and Barrel seizures his lens have suffered are also way above the norm as these are physical they maybe point at transport or environment issues.

on the other hand if it was Pentax QC issues then surely every Pentax lens buyer would experience the same failure rates and though there is plenty of examples of poor service and quality they appear unlike Joe's isolated.

Even if you consider Pentax's two most fragile lens the 16-50 and 50-135 who at their peak appear to have been around 10% failure over 3 years (2008-2012) Joe is still considerably higher being around 75% failure over the same period.

As I don't believe in good/bad luck and trust Joe's 'reports' I'm left at a loss with only external/environmental factors left.

My own experiences are different though I have my share of failures ....

1 k10d blown main fuse (possibly my fault) Pentax replaced Camera FoC 1 month outside warranty

2 k5 sensor stain (changed by shop) Nov 2010

3 k5 sensor stain (changed by shop) Nov 2010

4 k5 sensor stain (changed by Pentax shipped from factory for me) Jan 2011 (Pentax were very good enuring I had camera at all times)

5 50-135 SDM failure Pentax replaced 4 year old lens with refurbished review unit FoC under UK 6 year 'design' warranty

6 q7 locking up still at repair (France)

Over the years I have or do own Pentax  (modern cameras and lens)  ... k10d, k20d , Kx ,k5 and k3 ..18-55,50-200,55-300,da*55,da*16-50,da*50-135,da*300,8-15,15-45 and 8mm.... Q and Q7  .. fgz360,fgz360 and fgz540

My failure rate is pretty much in line with what I experienced with my Canon FD and Eos film cameras in the 80-90's

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Jim King - Retired Colormonger - Suburban Detroit, Michigan, USA; GMT -4h (EDT)
Pentaxian for over 50 years.
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There is hardly anything in the world that some man cannot make a little worse and sell a little cheaper, and the people who consider price only are this man's lawful prey.
- John Ruskin
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A fanatic is one who can't change his mind and won't change the subject.
- Sir Winston Churchill
* * * * *
A fanatic is one who redoubles his effort when he has forgotten his original aim.
- George Santayana
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The difference between genius and stupidity is that genius has its limits.
- Albert Einstein

 awaldram's gear list:awaldram's gear list
Pentax K-x Pentax Q Olympus PEN E-PM2 Pentax Q7 Pentax K-3 +17 more
DAVID MANZE Veteran Member • Posts: 5,767
Re: Pentax Quality Control Strikes Again

awaldram wrote:

Jim King wrote:

awaldram wrote:

You perhaps are not aware how manufacturing works in the modern age

The only reason 'occasional' lens are checked is to ensure the lens are coming off the manufacturing line within 'acceptable defined limits. It has nothing todo with checking the lens itself (it doesn’t get a 'checked' stamp)

There I agree wholeheartedly with you!

Manufacturing plants use designs and build technique to achieve a set quality .... they then randomly check the plant is hitting that quality.

This doesn't mean things can't go wrong but is unlikely and even it it does not for an appreciable run before detected.

I don't think it's a problem with a production run as such, the problem is mostly with the couplets and triplets which cemented together the cement takes a while to set and the top elements "float" out of true, speaking to both Sigma and Tamron service department they both stated they were waiting for parts, when I enquired "what parts" they said the couplets, I probed further and they both blamed the out of alignment couplets to be the problem with my lenses. I phoned a Sigma a while later and was told the parts had arrived , a week later my lens was returned and was perfectly centered, the same was the case for Tamron decently centered.

The company I work for has a 2% limit for failing memory simms , One of the manufacturers we 'badge' has a 5% limit consequently we QC every simm from this manufacturer so that we can deliver on our 'promise' with our label.

The same applies to Joe even though it's manufacturer to user, Pentax obviously have a lower standard than Joe therefore the only way Joe can be sure to get 'what he requires' is to test every lens he buys, As his standard is greater than the manufacturers a good proportion will fail his test.

I'm not sure why we are always saying that "only Joe" has very demanding standards, don't we all when paying out $500 or much more for a lens? at least we would like a well centered lens, I know for the most part I insist on it at least to the point within 1/2 stop, that to me is acceptable. I've had F2.8 lenses where at F11 they still didn't resolve the out of balance plane of field. (Tamron 17-50mm/ Sigma 50-150mm both F2.8) The incidence of decentered lens I've purchased is frightning frankly, the latest is the (Tamron 150-600) I've just had notice a new one is on it's way.

This is because as designed they were never meant to pass his test hence he needs the better ones off the production run rather than average.

Pentax on the other hand couldn't care less they set their 'standards' to keep returns and warranty repairs to an acceptable level and if they can put two milk bottoms on a pepsi can and sell it for £1000 with low return they will.

To assume otherwise shows a level of brand blindness that is the true 'fanboy state' to believe Pentax make lens as a service to their users rather than make money !!! and leads to the disillusioned rants we often see in these forums ..... hell has no fury like pentaxian spurned

Andrew, wouldn't you expect to something close to a standard distribution of "quality" around the center point of the design spec, with outliers and and beyond the edges of the spec? if so, even if Joe's acceptance criteria are higher than Pentax's limits, I would think that he would still see a good proportion of acceptable lenses, with a few outliers. Instead, most of the lenses he gets seem to be unacceptable to him. Either his standards are absurdly high (and I don't think this is the case), his testing methodology is faulty, or he has had an extreme run of bad luck...

Your thoughts?

I would agree and honestly don't know why Joe suffers such high failures.

Probably because like me he checks his lenses, once bitten twice shy, a lot of folks find out a lot later on. Actually if you read Photozones reviews you will find Klaus Schroiff is "always complaining about de-centered lenses" (especially Sony's) often needing up to three copies to find a decent one, I think it would be hard to argue with his expertise.

I trust Joes testing so when he says a lens is d-centered I'm confident it is (at a level that easily users see-able)

I trust his findings because they equate with mine! I noticed already a few complaints of decentered DA 16-85mm copies in the very short time of their production. Photozone will be testing this lens soon!

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A fanatic is one who can't change his mind and won't change the subject.
- Sir Winston Churchill
* * * * *
A fanatic is one who redoubles his effort when he has forgotten his original aim.
- George Santayana

P.S. Love that quote BTW.

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Dave's clichés

 DAVID MANZE's gear list:DAVID MANZE's gear list
Nikon D750 Nikon D500 Nikon AF-S DX Nikkor 16-85mm f/3.5-5.6G ED VR Nikon AF Nikkor 24mm f/2.8D Nikon AF Nikkor 28mm f/2.8D +16 more
OP Joseph Tainter Forum Pro • Posts: 10,996
Re: Pentax Quality Control Strikes Again
3

awaldram wrote:

The same applies to Joe even though it's manufacturer to user, Pentax obviously have a lower standard than Joe therefore the only way Joe can be sure to get 'what he requires' is to test every lens he buys, As his standard is greater than the manufacturers a good proportion will fail his test.

This is because as designed they were never meant to pass his test hence he needs the better ones off the production run rather than average.

Actually, what I expect is a lens that is not defective.

Here's one I took in Tunisia last summer, with my first copy of the DA 55-300. Note how weak the left side is compared to the right.

Joe

DAVID MANZE Veteran Member • Posts: 5,767
Re: Pentax Quality Control Strikes Again
1

Joseph Tainter wrote:

awaldram wrote:

The same applies to Joe even though it's manufacturer to user, Pentax obviously have a lower standard than Joe therefore the only way Joe can be sure to get 'what he requires' is to test every lens he buys, As his standard is greater than the manufacturers a good proportion will fail his test.

This is because as designed they were never meant to pass his test hence he needs the better ones off the production run rather than average.

Actually, what I expect is a lens that is not defective.

Tell it like it is, I'm with you on this one!

Here's one I took in Tunisia last summer, with my first copy of the DA 55-300. Note how weak the left side is compared to the right.

Joe

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Dave's clichés

 DAVID MANZE's gear list:DAVID MANZE's gear list
Nikon D750 Nikon D500 Nikon AF-S DX Nikkor 16-85mm f/3.5-5.6G ED VR Nikon AF Nikkor 24mm f/2.8D Nikon AF Nikkor 28mm f/2.8D +16 more
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