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09-04-2008, 04:01 PM   #16
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QuoteOriginally posted by jamesm007 Quote
Yes you have found a problem I clearly see it and IMO 90% for sure you have softness in the corner; however its a common problem with that lens because it extends to zoom out. Here is a quote from dpreview review of that lens go take a read of the whole review if you like -

"One clear issue with our sample was extreme softness at the edge of the frame when shooting at wide angle and in portrait format, especially with the lens angled sharply upwards (perhaps not a common shooting situation, but distinctly noticeable in some architectural shots). We can only speculate that this could be a decentring phenomenon due to the play in the lens barrel when fully extended at 16mm."

So it seems you are not alone and the barrel is prone to movement. I am not sure what to advise but the softness at f8 is not that bad and is fairly deep into the corner.
I forgot to mention that the above two shots are at 45 mm, but maybe it doesn't matter. I agree that in these tests it doesn't look too bad... I still haven't figured out if this is related to my landscape shots. I guess the only question is whether to send the lens for repair. It should still be under warranty... though I am not the original owner but I do have the receipt, so I guess they wouldn't know...

09-04-2008, 05:01 PM   #17
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Sorry missed that you already read the dpreview. Personally I would try to get it fixed under warranty.
09-04-2008, 07:50 PM   #18
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Shim it

VERY gently shim the fully extended lens with something like a piece of a sheet of thin paper and repeat the rotation tests. You may still have softness but it should remain in the same relative position if lens slop in the extended position is actually the problem.

H2
09-04-2008, 08:00 PM   #19
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QuoteOriginally posted by pacerr Quote
VERY gently shim the fully extended lens with something like a piece of a sheet of thin paper and repeat the rotation tests. You may still have softness but it should remain in the same relative position if lens slop in the extended position is actually the problem.

H2
I might try this sort of thing, but the brick wall tests, newspaper etc. were all at 45mm focal length, which on this lens is the fully _retracted_ position. Yes, it is sort of backwards that way.

Edit: just played with the lens. It definitely shifts around with gravity as you rotate it, fully retracted and fully extended. Probably about a millimeter or something. Does seem a little "loose."

09-04-2008, 08:51 PM   #20
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Not just the front barrel, but one of the inner element molded in plastic barrel (about 5mm thick) is being guided by 3 Teflon rollers which were screwed on by hand w/o any sort of preciseness. Any of these 3 rollers could be not perfectly perpendicular and misalignment is guarantee. I have this lens for 2+ years and your samples look no worse than mine. The structural design of this lens is a recipe for optical misalignment after seeing how the lens was put together (a trend since the late FA series). IMHO, this lens is great for snaps at close range, but rather weak for landscape where you need sharp details corner to corner. But I must praise how they come up with the quick-shift mechanism which is so tiny yet effective. Unfortunately, it has come a little too late, as usual for Pentax, and we are now marching toward SDM (if Pentax shall live).
09-05-2008, 08:09 PM   #21
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Just tried a quick newspaper test again, first with just the camera on the tripod in portrait mode, then again with me physically pushing upwards on the front of the lens barrel (moves a little bit).

The first shot was the same as before (sharp bottom edge, soft top), the second shot was sharper up top and softer on the bottom, but much more symmetric, with sharp centre and softness slowly increasing as you move to the edge. Centre sharpness was the same, so me touching the camera on the tripod doesn't seem to have induced shake (it was a relatively fast shutter speed).

Also odd is that it seems that the effect might be lessened at wider apertures. It actually seems to be sharper in the upper corner at f/4 than f/8 (gets better beyond that). Maybe just depends on how you jiggle the lens.

Anyway, I guess I'll take it to the local Pentax repair centre and see if they can tighten it up or something as the issue definitely seems related to lens wobble. Of course this is a little scary as things currently seem fine in the usual landscape orientation that I use something like 70% of the time.

Interesting info wlachan... but it seems that quite a lot of people really like the optical quality of this lens, so I'd like to think it can be better.
10-17-2008, 12:30 PM   #22
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Update:

I took the lens into the Pentax Authorized Repair Centre here in Vancouver, and they told me that they would have to charge me $35 to send it to Pentax Canada, even though it was under warranty, so it would be cheaper for me to send it myself. Apparently the only service they actually do themselves is sensor cleaning.

So, I sent the lens to Pentax Canada a month ago. Today I got an estimate back from them for $137.54 despite the lens still being under warranty.

It says "item is impact damaged" and lists $7.80 for a lead ring (?), $5.00 for "digital miscellaneous" and $100 for labour. Once you add on another $10 for shipping it back to me and taxes the total is $137.54.

I know for sure that I did not "impact damage" this lens. But since I got it used, I suppose a previous owner could have. I guess I could argue, but maybe it is "obvious" to them that someone dropped the lens and they'll call me on it. I am leaning towards just paying up and getting my lens back, but when you add up the $275 I paid, but $25 to ship it back to them, plus this $137 you get $437 which is way more than I would have paid if I'd just bought it new.

Oh well, I guess thats the gamble you make when buying used... lens wasn't really all that bad though, which is what makes it more annoying. If the lens was totally busted, I'd happily pay $140 for a working DA16-45, but i don't know if I'm even going to notice. Maybe it was more broken than I realized.
10-17-2008, 05:16 PM   #23
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too bad about the lens ... maybe next time you can ask for full size samples?
what are you going to do now?

10-17-2008, 06:08 PM   #24
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QuoteOriginally posted by k100d Quote
too bad about the lens ... maybe next time you can ask for full size samples?
what are you going to do now?
I did get full size samples, and they looked fine. The problem was only noticeable with the lens in certain orientations, and even then, not usually obvious, unless you were taking a picture of a brick wall or newspaper. I was only able to notice it after using the lens for some time.

I might mention to pentax that I did not drop it, but presumably that is what some people who DO drop lenses tell them too. I'll just pay and hope that the lens is actually better I suppose. I guess I'm just unlucky that the first time I buy a used lens it has problems. Certainly turned me off the used market. I guess on average you will save money buying used, even if occasionally you have a problem like this...

One highly annoying thing is that Pentax received the lens on Sept. 11 (I can tell from the tracking). The estimate was prepared on Sept. 30 (dated on the sheet). This I guess I can excuse as perhaps they are busy. But I only got the actual estimate in the mail today, October 17! Usual mail delivery time for that distance is about 3 days. So essentially my lens sat on the shelf for 2 weeks for no reason. Too bad they didn't use the email or phone number I sent them, which they even noted down on the estimate sheet. Oh well.
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