Sunday, September 02, 2007

De-centering Defects of Pentax Lenses

Klaus Schroiff of the PhotoZone recently has cancelled his tests on both of the two latest DA* zooms, owing to the pronounced "centering defects" found. In fact, he has already found so many and too many similar defects with Pentax lenses during his tests on Pentax lenses carried out up till now. With those centering defects found, Klaus either re-acquired another sample from the PhotoZone community or he simply cancelled the tests, which is indeed a rather disappointing thing, especially when this keeps repeatedly happened, very unfortunately.

A search of the term "centering defect" in the PhotoZone forum datebase using its search function will reveal how many times this problem has been appeared and reported during the course of his testings in recent months. I'm actually not being totally surprised for having alignment issues with Pentax products from my own "unfortunate" experience, especially for the recent Pentax products which were made and are being made outside Japan.

Nevertheless, I am a bit sceptical about if it is really about the poor QC of the Pentax lenses instead of the mis-alignment of Klaus's K10D body instead. Coincidently, I have asked Klaus the similar questions more than twice in different posts in which he reported the problem when he tested different Pentax lenses (which I can see many of the conversations again when I have done the search on the keywords "centering defects". Below were some of his answers to my questions:-

http://www.photozone.de/active/forum/ShowMessage?ID=108899021463946422146394641A

"This is very unlikely. There were no significant centering defects in the Tamron 70-300, Cosina 100 and the Sigma 10-20 tests - these were among the most recent test runs in Pentax land."

http://www.photozone.de/active/forum/ShowMessage?ID=108552321463980702146398065A

"An asymmetrical centering defect isn't all that severe from a testing perspective.
If I reject a lens it is mostly because the _center_ portion shows both sharp (although suboptimal) edges as well as "edge shadows". In the real life this kind of defect shows up as weak contrast but not as asymmetry."

Here is a capture of the *image center* for a chessboard like resolution chart pattern:-

http://www.photozone.de/active/forum/ShowMessage?ID=10829312146400715A

As we can see from the above diagram, asymmetricity or the phenomenon of directional "edge shadows" does really exist. As Klaus has mentioned in so many of his Pentax lens review and posts about his tests that there are centering defects in common (more or less), objective facts tell me that I should admit that there is a problem with even the Pentax optics, despite I have already tried to think objectively about any other possibly cause and asked for times if "it should be the body". (Well, I do not have very good faith or impression on the quality control and perfect alignment of the K10D body but I can't imagine even a bundle of different Pentax lens models could have serious alignment problem - even for the optical center).

Very interestingly, MTF tests like those conducted by Photodo indeed can already show the presence of centering defects, as cleverly pointed out by this PZ poster:-

http://www.photozone.de/active/forum/ShowMessage?ID=1082931214640066121464006602146400658A

Now, the DA* 16-50 and DA* 50-135 samples which have been got from the street have very significant and pronounced centering defects. Despite the tests have been cancelled and Klaus will not publish the test results formally anymore, he is yet kind enough to post briefly the unpublished results in his forum:-

http://www.photozone.de/active/forum/ShowMessage?ID=10889902146394636A

Well, as we can see, actually both DA* perform not so well especially for the poor/low resolution at wider apertures and at the image borders as well as the huge amount of CA present. Whilst the centering defect, which is found to be existent in both DA* lenses, could affect image quality and "spoiled the MTF figures a bit", which has been verified, here, possibly the lenses' optical performances are not that good by themselves. As remarked by the tester, the inferior CA performance is just "Tokina alike".

Last but not least, as those lens samples obtained are new products which have passed the factory QC and those are acquired from the streets, we may think it in the following two additional possible ways:

1. The de-centering amount is just within Pentax's factory specs but should not be considered as a defect by Pentax's own standard - but then Klaus compared the Pentax lenses from Canon, Nikon etc. or even to Sigma and Cosina (on the same K10D) but he found that particular Pentax lenses are worse, including even the latest "luxury" DA Star zooms;

2. Those samples put under test are just lemons and they leaked through the Quality Control system/net from the factory - if so, I'm afraid that the QC system of Pentax is really rather ineffective or even useless as there are so many bad samples out there as picked up in the streets and ultimately been borrowed/bought by Klaus and very unfortunately even been put to the lab test.

All in all, my opinion is simple: for lower priced lenses, such defects are more acceptable as the customers should get what they paid (for). However, for "Star" lenses that marked with a new golden "Star" label on them, with a "Star" price, shouldn't we expect a "Star" quality also, in terms of *real* stringent QC tolerance and inside performance as well.. But, so far from what we can see from all those specific adverse user or even test reports of the new DA Star lenses (which are shown together with quite some evidences), I'm really afraid that our above assumption has not been proved valid and maybe even just wishful thinking of we Pentaxians. Really sad.. :-(

10 Comments:

Anonymous said...

Please add Klaus's own verdict on centering defects in general. And this is for ALL brands w/ the possible exclusion of Olympus which seems to have the least amount of these sort of issues:(If there sensor wasn't so small and lenses EXPENSIVE I'd probably buy one.)
...........................
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
http://www.photozone.de/active/forum/ShowMessage?ID=108899021463946242146394623214639462021463946172146394601214639458921463945792146394578A
Not to defend Pentax but you will find these sorts of issues in L glass ect.. Just the state of the world........................
http://forums.dpreview.com/forums/read.asp?forum=1036&message=24633354
"I could mention countless bad lenses and cameras that I've encountered...The one that really comes to mind is the $4200 Canon 5D and 24-105L combo...The 5D viewfinder/prism had 4-5 hairs when opened brand new...No internal cleaning helped so I sent it in since many others were finding the same so I doubted a replacement would be any better...At this point the 5D iteself focused OK...However the 24-105L had what I assumed was a decentered element as about 30% of the entire left side remained soft even when stopped down to f11...It was outright blurry wide open...So I sent the camera to be cleaned and opted for a replacement 24-105L...When I finally had both together again they showed a dramatic front focus even though the 5D was fine with 3 other Canon lenses....So I sent them both to Canon and yes they came back spot on...So kudos to Canon for finally getting me an acceptible product..."
But then again you won't actually pay any attention....and no this is not any more acceptable than getting a bad copy of an "L" lens. I assume you think that these things don't happpen anywhere else???

Anonymous said...

More bad examples of Canon glass:
>>>>>>>>>>>>>>>>>>>>>>>>
The centering defects as someone stated earlier are not limited to just the Pentax models, many reviews even of Canon L glass have had the exact same issue. Generally in this case he will test multiple copies (he tested 4 consecutive copies once of a L series piece of glass and only on the 4th did he achieve a proper test bed).
As for the Canikon glass, I just purchased a 24-105 and a 70-200 f4 and it took me 3 different copies of the 24-105 to find a sharp lens and 2 field tests to get a good 70-200 f4. So yeah, even Canon users have the same problems and we're paying for supposed "Luxury" glass.
http://www.pentaxforums.com/forums/pentax-slr-lens-discussion/11374-photozone-cancels-testing-new-da-lenses-2.html
>>>>>>>>>>>>>>>>>>>>>>>>>>>
Flare problems:
It is worth to mention that this lens has been serviced by Canon due to the flare problem present in very early production lenses.
http://www.photozone.de/8Reviews/lenses/canon_24105_4_is/index.htm
>>>>>>>>>>>>>>>>>>>>>
And I could go on and on and on......

Anonymous said...

Found one more interesting comment from Klaus:
Klaus Schroiff wrote:
> If it feels better - the long term quality of Canon IS / Nikon VR
> lenses is pretty bad ... this is at least nothing to worry about in
> Pentax land.
Since as he put it IR/VR is just "controlled decentering" it seem like he feels this is a recipe for future failure as the antishake parts start to wear...

CuriousOnlooker said...

Anonymous, you're wasting your time writing a defense. Rice High has already come to the conclusion that Pentax makes second-rate equipment, and sees any defense of Pentax as fanboyism. Rice High makes many conclusive-sounding statements about the DA 16-50, but the bottom line is that these "facts" are based on hearsay. Simply put, he hasn't used the lens himself and merely picks and chooses negative news to post.

In reality, there have been both positive and negative postings on various forums about the DA 16-50, and he has chosen to emphasize the negative (yet again).

Olivier said...

Yesterday, in the evening, I could read 18 (eighteen) comments. Some didn't agree with you.

Did you have a server problem or a ego problem, highrice ?

RiceHigh said...

Boy, I've made a new blog entry already! It seems that you've just got crazy and thus having blind eyes. Anyway, I hope you could stay calm. Take care!

Anonymous said...

As I figured. Turn a blind eye to the truth....Sad. Hey were are those side by side shots???

Anonymous said...

To curiousonlooker. Yes I know, but like a moth to a flame I am drawn to this "tabloid style reporting". It's like a gossip column. Not to mention I consider it my duty to couterpoint a bit. What really infuriates me is the "I'm really trying to help Pentax" but in actuality is quite counter productive. Now the 16-55 is still an open debate but as I tried to show, and as he so lamely just ignored, is that these things do happen to all companies.Someone once told me to never argue with a moron. Apparently I didn't listen. And technically the posts are not for him but to give others a chance to do what they should do. Consider all sources and not let one doofus decide for you.

RiceHigh said...

> CuriousOnlooker said...
> Anonymous, you're wasting your time writing a defense. Rice High has already come to the conclusion that Pentax makes second-rate equipment

Really? Have you seen this (of mine)?

Anonymous said...

SIGH.... still tripe coming out of you? Anyway no comments to Klaus's decenetering estimates???? Seems he should be in a position of authority. Not you......
Looks like I wouldn't want to take a chance buying a Canon 24-105L. Would you after all the bad reports ;)

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