[slava]

How about this: You can believe what you like based on your experience, and I'll believe what I like based on mine... fair enough?

.

Yes, absolutely fair enough. Everyone has right to his own opinions🙂

But let me explain why my opinion was so definite. I own one decentered lens. This is the old zoom FA 24-90 and photos taken with it look identical to the test photo which is being discussed here. The left side is blurry, dirty and is more prone to CA (Btw, did you notice there's more CA on left side of the test photo here? Please take a look). I tested my lens in many ways and indeed it is decentered. Based on this experience I drew my conclusion here. That's it.

Here's an article you might find interesting, from the always-informative-and-educational Roger Cicala at Lens Rentals:

Optical Quality Assurance - Lens Rentals | Blog

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I read it. Illuminating, indeed. Probably I required too much from Pentax. Thanks 🙂

---------- Post added 01-06-22 at 04:14 AM ----------

Welcome to the forum.
I find your two posts quite curious as they are both quite critical of Pentax. Although there is nothing wrong with expressing such opinion this seems strange for your first two posts on the forum. I truly hope criticizing Pentax wasn't your purpose in joining.
Perhaps you should sit back for a bit, review our forum rules, and peruse the forums to get a feel for the community. Maybe find a way to express your opinion without being quite so confrontational toward other members as your second post was.

No I didn't join the forum to critize Pentax. Actually the decentering issue is the only thing for which I am angry with them (however, I must admit that having read the article recommended by BigMackCam I am starting to be less angry&#128522. Besides, I'm a Pentax fan who collects their lenses . If my definite opinion seems confrontational to you I am sorry. It was not my intention, really. I only judged the based on the photo which imho looks badly.

[BigMackCam]

Close enough!

The reason for posting here was to get second opinions and help with looking at the samples as well as getting feedback from the reviewers. I should know by now that it's not possible on PF because very few users are willing/capable of just looking with their eyes at Pentax samples and seriously analyze potential issues (or rather users are unwilling to post in public about it because of the hassle they get, I know this from previous cases) There are always users that try to deflect any potential problems and turn a simple exercise of analyzing samples into strange irrelevant discussions about brand loyalty.

I think you do your fellow members a disservice, @house - I've looked (yes, with my eyes - how else?) and considered the potential cause of the softness... and I've agreed that it could be de-centering or tilt. I just don't think the evidence is conclusive, and I've expressed why.

On the one hand you want second opinions, while on the other you don't seem to like them when they don't match yours, pose alternative scenarios and/or suggest you may be wrong - which is exactly how @ChristianRock and I responded. But you also need to factor in that you have, as I recall, some considerable history of appearing (perhaps unintentionally?) highly critical of Pentax... of picking fault. So, there's an element of assumption from others, I think, that when you point out an issue it's just another one of your criticisms, when in fact sometimes you have perfectly valid concerns. Honestly, I often make that assumption with your posts - but I'll try to give you the benefit of the doubt more often in future...

I've explained to you before that I don't "do" brand loyalty, and I've been critical of Ricoh and several items of Pentax equipment in the past... but I do try to offer balance, relevant opinions and reasoning in discussions where there's criticism of the brand and its equipment. These forums are - as I already mentioned - publicly viewable, with discussion thread links appearing in web search engine results. In some considerable measure, we are the public face of Pentax - what we discuss in these forums impacts how the brand is viewed by others, and I very much want it to remain successful. As such, I think it's important to openly discuss both sides of an argument when criticism is levelled. This is, after all, a brand-specific forum of enthusiasts, so you should fully expect challenges and push-back to criticism...

[house]

I think you do your fellow members a disservice, @house - I've looked (yes, with my eyes - how else?) and considered the potential cause of the softness... and I've agreed that it could be de-centering or tilt. I just don't think the evidence is conclusive, and I've expressed why.

On the one hand you want second opinions, while on the other you don't seem to like them when they don't match yours, pose alternative scenarios and/or suggest you may be wrong - which is exactly how @ChristianRock and I responded.

Those comments about how to read the samples are all fine to me. I have no issue with people reading the samples differently. I might articulate why I think those readings are mistaken but I would hope to hear back with further precision about the thinking around it. The depth of field thinking is imho shown by the statue photo to be a red herring at 21mm f4 since both statue and building are reasonably sharp at f4. In fact surprisingly sharp. https://www.photopills.com/calculators/dof

[Sandy Hancock]

This thread seems to have run its course.

Some photos in a review show some problems. They may (or may not) be due to sample variation, which is an issue with every mass produced lens ever made. Why that is even a subject for discussion is beyond me.

If there is nothing worthwhile to add, closure is imminent.

[BigMackCam]

Those comments about how to read the samples are all fine to me. I have no issue with people reading the samples differently. I might articulate why I think those readings are mistaken but I would hope to hear back with further precision about the thinking around it. The depth of field thinking is imho shown by the statue photo to be a red herring at 21mm f4 since both statue and building are reasonably sharp at f4. In fact surprisingly sharp. https://www.photopills.com/calculators/dof

At this point, I'll leave you to your analysis. Whatever the reason for the softness observed, it's a single sample of a lens that otherwise reviewed extremely well. As such, I see no value in trying to prove whether de-centering or tilting was present on this individual lens. If it's somehow proven that one or both of these flaws was present (for which you either need access to the lens, or else convince Bernard to run additional tests), I don't see that we gain anything. But if your curiosity is piqued, you have the time and you'll get satisfaction from investigating this, have at it

[house]

This thread seems to have run its course.

Some photos in a review show some problems. They may (or may not) be due to sample variation, which is an issue with every mass produced lens ever made. Why that is even a subject for discussion is beyond me.

If there is nothing worthwhile to add, closure is imminent.

Sandy what about the sharpness tests if a damaged lens was used? I really struggle to understand why anyone would like to shut down a tread looking into this. The tone isn't that bad compared to other treads? If less posts were made about meta issues this thread would be appropriately slow with only people finding new 'evidence' or coming up with new readings posting.

Edges and corners, while usable, never reach the same resolution as the center.

"While usable" may become good or excellent with a good copy. Isn't it worth a bit of thinking and discussion to figure out if this is the case rather than letting a somewhat lackluster review sit there as the only review on the web. I can't see what anyone has to win from that scenario.

Back to the samples. The https://themotec1.netfirms.com/Users/Hosted/cdn/carl/DFA%2021/Samples/bdery/13.jpg image is actually very hard to explain without tilt.

1. The focus is on the statue (50m or more in front of the building?)
2. The left hand side of the building is closer to the camera than the right as seen by looking at the horizontal lines. The roofline goes down as it goes left whilst the ground goes up. Perspective means that the left part is closer to the camera.
3. Despite being closer to the focus point the left side is significantly more blurry than the right. Imho only tilt or other flaws could create this effect.
4. The sharpness of the right hand side of this photo and the distance between focus point and building shows that depth of field or curvature doesn't explain sample https://themotec1.netfirms.com/Users/Hosted/cdn/carl/DFA%2021/Samples/bdery/9.jpg where the plane of focus is nearly square on the building as seen in the near horisontal lines. The difference in distance to viewer between left and right is only a fraction of the distance between statue and building in the other shot. Despite this the right hand side is reasonably sharp in the statue photo.

There's a separate discussion about what performance is within spec. Only Pentax can answer that authoritatively. Users can only decide on their personal limits.

Mike the only reason a faulty lens is of interest to others than the owner is when the performance of the whole lens design is publicly determined based on that faulty sample. To me that's obvious.

[gatorguy]

I think the thread has run it's course. There is not going to be a definitive answer so it's devolved into the same talking points rehashed. And then re-re-hashed. Closing this thread so we can all move on to better things.