[tibbitts]

I hope everyone who sends in a lens in for what appears to be decentering issues will report their experiences. Honestly I'm not sure decentering can be "fixed", at least without replacing a good chunk of the lens, because of how modern lenses seem to be composed of integrated element groups. I just don't know how much adjustability is built-in compared to older generation lenses. It would be interesting to hear from an expert on that issue.

My experience was that I couldn't get the lens fixed/replaced, even within warranty, because it wasn't deemed to be bad enough.

Regarding the 1 year warranty, remember that buying with a credit card (at least in the US) gets you a second year free. Of course that might just buy you a second year of not being able to convince the manufacturer to fix/replace the lens.

[nicoprod]

Always the same discussion about lenses being soft wide open... If you want to use your FA31 wide open, do it in dim to moderate light, and somewhat close to your subject. That's what it's for. The closest you get to infinity, the softer and unreliable it gets. Your lens is just a tool, it has specs, It's not mother Teresa.

[ironlionzion]

I hope everyone who sends in a lens in for what appears to be decentering issues will report their experiences. Honestly I'm not sure decentering can be "fixed", at least without replacing a good chunk of the lens, because of how modern lenses seem to be composed of integrated element groups. I just don't know how much adjustability is built-in compared to older generation lenses. It would be interesting to hear from an expert on that issue.

My experience was that I couldn't get the lens fixed/replaced, even within warranty, because it wasn't deemed to be bad enough.

Regarding the 1 year warranty, remember that buying with a credit card (at least in the US) gets you a second year free. Of course that might just buy you a second year of not being able to convince the manufacturer to fix/replace the lens.

Did you send your lens into CRIS or directly to Pentax? My 31mm is still boxed up and about to ship, but I'm wondering if I'd be better off selling it at a discount on Ebay (declaring the decentering). Here's at picture at f5.6 from my 31mm showing the decentering. Fortunately, it only shows up on the far right of the image and is only somewhat noticeable at 100% on my 24 inch monitor. It's significant enough to me that I'm going to have to repair it or sell it. In my crop of the right side, you can see that the bottom bush is actually in focus, but the mid and far back bushes are totally blurred. Actually, the rock on the bottom right corner is actually in decent focus. Though this picture isn't a good example, the left side of the image is completely sharp.

[nicoprod]

it only shows up on the far right of the image and is only somewhat noticeable at 100% on my 24 inch monitor

What's wrong?

[normhead]

I hope everyone who sends in a lens in for what appears to be decentering issues will report their experiences. Honestly I'm not sure decentering can be "fixed", at least without replacing a good chunk of the lens, because of how modern lenses seem to be composed of integrated element groups. I just don't know how much adjustability is built-in compared to older generation lenses. It would be interesting to hear from an expert on that issue.

My experience was that I couldn't get the lens fixed/replaced, even within warranty, because it wasn't deemed to be bad enough.

Regarding the 1 year warranty, remember that buying with a credit card (at least in the US) gets you a second year free. Of course that might just buy you a second year of not being able to convince the manufacturer to fix/replace the lens.

My experience would suggest you want to be dealing with a seller that will do an over the counter exchange if you judge the lens to be defective within 7 days of purchase. I use mail order, and Henry's gives me two weeks. Essentially, I don't want to pay for a defective lens. I am willing to pay for a lens that works perfectly. Not a lottery shot at a good lens, I don't care who messed up, bad at the factory, dropped during shipping , dropped in the sellers warehouse, I don't care where or how it got knocked out of alignment or it ever was in alignment, I am only willing to pay for a good lens. Henry's took back two Sigma 120-400's before I gave up and bought the 60-250. And I could have gone for a total refund of my money. The law in Canada says I have 7 days I believe, Henry's adds another week to that because it's mail order, what they think about the lens is irrelevant, if for any reason I say it's not good enough, even if I made a mistake and ordered a lens that wasn't good enough (as in the second 120 to 400, it was working up to spec, I just didn't like their spec), they take it back. That's what you want to be dealing with.

The day I get a new lens, I run it through the mill, closeups, distance shots, low light , into the sun and backlit subject... if there's any question in my mind it goes back.

[ironlionzion]

What's wrong?

The lens focuses to 10 ft on the far right side of the image when set at infinity.

[nicoprod]

The lens focuses to 10 ft on the far right side of the image when set at infinity.

Where is your focus point set at?

[ironlionzion]

Where is your focus point set at?

I always use center point. It was focused at the main building. This is at f5.6. I have several other examples that all show the same blur only on the right side. I normally don't use my 31mm for landscape (usually just for portraits or other pics near wide open) so it's not noticeable on most of the pics from the lens.

[tibbitts]

My lens was a Sigma EX sent to the manufacturer, so not a Pentax experience. However I have a Pentax lens that I corresponded with Pentax about, but didn't bother sending in. I still have it. I'm just not convinced the repair facilities have the ability to test or repair these kinds of issues. If the inner barrel falls out or the mount falls off, they can fix your lens. Performance problems I think are hit-or-miss - you might end up with something better or worse.

That brings up the question of what to do if you want to sell the lens and try again, armed with a better ability to test/reject bad copies based on your experience. Say you have a lens that you know, on the basis of comparison with another of the same model, really isn't correct and underperforms enough for you to not want it. But the manufacturer tells you it meets factory specs, maybe multiple times. Is there really a problem and do you disclose the problem when selling? Would you feel differently about selling/trading to an expert in the photo business, who can presumably test and make conclusions for themselves, vs. a consumer? Obviously the manufacturer considered it good enough to sell, so what do/should you do?

[nicoprod]

I always use center point. It was focused at the main building

If it's focused on the main building at 5.6, you can't expect objects that are standing 20 ft in front to be in focus to. Looking at this image it looks like the focus is in the middle, that bush on the foreground seems to confirm that. An image like that you need to stop it down to f11.

[tibbitts]

My experience would suggest you want to be dealing with a seller that will do an over the counter exchange if you judge the lens to be defective within 7 days of purchase. I use mail order, and Henry's gives me two weeks. Essentially, I don't want to pay for a defective lens. I am willing to pay for a lens that works perfectly. Not a lottery shot at a good lens, I don't care who messed up, bad at the factory, dropped during shipping , dropped in the sellers warehouse, I don't care where or how it got knocked out of alignment or it ever was in alignment, I am only willing to pay for a good lens. Henry's took back two Sigma 120-400's before I gave up and bought the 60-250. And I could have gone for a total refund of my money. The law in Canada says I have 7 days I believe, Henry's adds another week to that because it's mail order, what they think about the lens is irrelevant, if for any reason I say it's not good enough, even if I made a mistake and ordered a lens that wasn't good enough (as in the second 120 to 400, it was working up to spec, I just didn't like their spec), they take it back. That's what you want to be dealing with.

The day I get a new lens, I run it through the mill, closeups, distance shots, low light , into the sun and backlit subject... if there's any question in my mind it goes back.

I do this now, and completely agree. Back in the film days I never did this, but was also never disappointed in any of my lenses (admittedly somewhat more conservative Pentax and Canon designs than the Pentax/Sigma/Tamrons that I have now.) So when I started with digital I wasn't critical enough and got stuck with some clunkers before I gradually learned (and continue to learn) how to test what to look for. Also I think as we move up to higher-res bodies, lenses that appeared fairly consistent across the frame at, say, 6mp, might not appear that way at 36mp.

[ironlionzion]

My lens was a Sigma EX sent to the manufacturer, so not a Pentax experience. However I have a Pentax lens that I corresponded with Pentax about, but didn't bother sending in. I still have it. I'm just not convinced the repair facilities have the ability to test or repair these kinds of issues. If the inner barrel falls out or the mount falls off, they can fix your lens. Performance problems I think are hit-or-miss - you might end up with something better or worse.

That brings up the question of what to do if you want to sell the lens and try again, armed with a better ability to test/reject bad copies based on your experience. Say you have a lens that you know, on the basis of comparison with another of the same model, really isn't correct and underperforms enough for you to not want it. But the manufacturer tells you it meets factory specs, maybe multiple times. Is there really a problem and do you disclose the problem when selling? Would you feel differently about selling/trading to an expert in the photo business, who can presumably test and make conclusions for themselves, vs. a consumer? Obviously the manufacturer considered it good enough to sell, so what do/should you do?

(Sorry to hijack this thread)

Here's another example of my decentering

Full pic, center near focus point, left side, and problematic right side.

---------- Post added 03-23-14 at 06:32 AM ----------

If it's focused on the main building at 5.6, you can't expect objects that are standing 20 ft in front to be in focus to. Looking at this image it looks like the focus is in the middle, that bush on the foreground seems to confirm that. An image like that you need to stop it down to f11.

The second picture shows objects in the plane of focus. Like I said, on the right side of the image, objects that are 20 ft in front are in focus, even though focus is set at about 200 yards.

[ironlionzion]

Here's an example at f2.8, where the image shows significant blurring on the right side even at websize, and the affected area is greater. Check out those rocks and the blurred snow on the right. Compare with the left side.

[tibbitts]

Always the same discussion about lenses being soft wide open... If you want to use your FA31 wide open, do it in dim to moderate light, and somewhat close to your subject. That's what it's for. The closest you get to infinity, the softer and unreliable it gets. Your lens is just a tool, it has specs, It's not mother Teresa.

So how should a consumer know what the lens "was meant for?" An FA31 isn't, for example, a Medical Nikkor, which was very obviously designed for a particular purpose. I've bought several Pentax prime lenses. Since I never had an issue with any of them wide open at infinity (well, other than the general not-quite-as-good wide open vs. stopped down a little characteristic that I think everyone would expect), why should I anticipate such a limitation with the FA31? Where in the specs would a consumer look to find a clue to this?

[nicoprod]

Here's an example at f2.8, where the image shows significant blurring on the right side even at websize, and the affected area is greater. Check out those rocks and the blurred snow on the right. Compare with the left side.

I kind of see what you mean. Can you take a picture of a brick wall at 5.6 or a cereal box at 2.8? I think it would be easier to determine if there's something wrong with your fa31.

---------- Post added 03-23-14 at 11:48 AM ----------

(well, other than the general not-quite-as-good wide open vs. stopped down a little characteristic that I think everyone would expect

That's all I mean.