[Tbear]

Both lenses had "pronounced centering defects". The link discussing this at Photozone:

Show Message

Ted

[LeoTaylor]

I read through the dozens of replies to the thread and I was not impressed. Some asked the reviewer to explain "centering defect", how it was measured, and how much error is considered severe. I did not see an answer.

As Johnny Five said, "Need More Input."

[Tbear]

I read through the dozens of replies to the thread and I was not impressed. Some asked the reviewer to explain "centering defect", how it was measured, and how much error is considered severe. I did not see an answer.

As Johnny Five said, "Need More Input."

Klaus Schroiff, the owner of Photozone, has tested hundreds of lenses using what I believe are reliable methods. Thousands of photographers respect and look forward to his reviews. He does not seem biased against Pentax and has given many Pentax lenses favorable reviews. If he considers the centering defect to be enough to cancel the review, then I consider that significant in my book.

Ted

[Ole]

Klaus Schroiff, the owner of Photozone, has tested hundreds of lenses using what I believe are reliable methods. Thousands of photographers respect and look forward to his reviews. He does not seem biased against Pentax and has given many Pentax lenses favorable reviews. If he considers the centering defect to be enough to cancel the review, then I consider that significant in my book.

Ted

I agree, and it would be nice to see a reaction from Pentax and hopefully some actions to improve assembly quality. I'm happy that I have secured some FA* lenses while I could.

[m8o]

one has to wonder what's behind all those delays in releasing the new DA* lenses after all... Maybe Hoya will succeed with crack'n the whip!

[jamesk8752]

Note that Klaus is willing to test a second set of lenses should someone provide them, and also that he has seem many decentering defects with Canikon lenses as well. Pentax is not the only company with lens QC issues...

It is a shame, though, that Pentax doesn't do a better job of QC on their premium DA* lenses. At that price point it would seem to me that they could afford the cost of individual lens testing to confirm good performance.

[jeffkrol]

and a bit of a black eye for Pentax. But apparently not that uncommom across the board: See Klaus'es own "estimate". I would have loved for Pentax to "beat the odds" though but apparently this is not the case.
1. all lenses are decentered - a perfect sample does not exist
2. expect 10% of the lenses to be severely decentered
3. expect 15% (+10%) of the lenses to be sub-standard
Show Message

Note that Klaus is willing to test a second set of lenses should someone provide them, and also that he has seem many decentering defects with Canikon lenses as well. Pentax is not the only company with lens QC issues...

It is a shame, though, that Pentax doesn't do a better job of QC on their premium DA* lenses. At that price point it would seem to me that they could afford the cost of individual lens testing to confirm good performance.

[Wethphotography]

I hope Ned Bunnell or someone from Pentax reads this forum or Photozone and provides Klaus with more samples.
For what it is worth, my copy of the DA* 50-135 seems to very good; I haven't used it enough to declare it perfect, but I am pleased with the photographs I have made with it. The DA* 16-50 is another matter, maybe Klaus ended up with the copy I returned....

[GaryML]

I hope Ned Bunnell or someone from Pentax reads this forum or Photozone and provides Klaus with more samples.

Photozone, i.e., Klaus, does not get test samples from manufacturers; he gets test samples from consumers who lend their lenses to Klaus for testing. I believe that Pentax does supply test samples to print publications like Popular Photography. You can judge for yourself whether Klaus' test methods are valid. He does not use an optical bench, but simply takes pictures through a digital camera and applies a software program for the test results. The consumer-supplied lens samples may have manufacturing defects, or damage from use and mishandling by whomever lent the sample.

The broader issue is whether Internet "journalists" are to be regarded as real "journalists" and entitled to the same privileges as traditional print journalists. Should they get press passes and access to the limited resources available to major newspapers? Is a guy with a blog on the Internet entitled to compete for one of the limited seats to an event reserved for the press against reporters from the New York Times or Wall Street Journal? This has become a significant issue when anyone can claim to be an "Internet journalist" simply by creating a Web site and putting any sort of stuff up on it.

[Tom Lusk]

What credibility could you give to a test done by a lens supplied directly from the manufacturer???

Do you think the manufacturer would randomly pick a lens off the production line and ship it off?

Sure, they would.

And to suggest Klaus got lenses from someone who mishandled and/or damaged them before lending them is really grasping at straws.

Saying that Klaus is "just some guy off the internet" is just shooting the messenger IMHO.

Pentax obviously has serious QC problems at their plants. There is no way these * lenses should be released with a high percentage of duds.

Like Ole, I am SO glad I have the FA* lens and the other quality glass I need.

[Wethphotography]

What credibility could you give to a test done by a lens supplied directly from the manufacturer???

Do you think the manufacturer would randomly pick a lens off the production line and ship it off?

Sure, they would.

Sounded a little naive, didn't I? Thanks Tom. I guess what I really should have said is that Pentax should get quality control straightened out and fast!

[m8o]

MTF graphs for any who didn't see the post:
http://www.photozone.de/active/forum/ShowMessage?ID=10889902146394636A

[little laker]

RiceHigh actually asked a very good question

Klaus, would it be your body? That is, the K10D? ..since you have found so many different Pentax lenses of different models or copies of the same models have the "centering defect" but you have only ONE body.

[jslifoaw]

RiceHigh actually asked a very good question

The body might be responsible for AF errors (which are a non-issue for testing), but in order for it to cause a problem otherwise, the CCD would have to be non-flat or not perfectly perpendicular to the lens' projection. This is unlikely given the previously recorded tests.

Also, rather than waiting for a review to tell you whether or not a lens is worthy of buying, a much easier way to decide as long as one is available locally is to simply obtain one and try it out. Shooting a distant landscape with detail in all areas is a very simple way to tell whether or not a lens is a lemon (four of mine were; I own none of them any longer).

As a student learning about probability and statistics, it's very easy to manipulate/interpret graphs to support just about anything, while maintaining their accuracy relative to the results they represent.

[jeffkrol]

Hope Klaus doesn't mind:


Tokina AF 16-50mm f/2.8 AT-X Pro DX (Nikon)- Photozone Lens Test Report / Review
Tokina:

Pentax:


Tokina MTF:

Pentax MTF:

MTF graphs for any who didn't see the post:
Show Message