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10-28-2018, 05:14 PM   #1
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Tammy 17-50 lens or K-5 body causing major issues - return lens or replace body?

Hello,

I hope someone can help. I recently purchased a new Tamron 17-50 f/2.8 because my old one seemed way out of focus when shooting at infinity. I've come to realize that the old lens was actually severely front-focusing. It had, in the past, developed the dreaded loose front element, which I fixed myself. I thought I had maybe not tightened up the front element properly (some may know that the front element can be loosened and rotated in and out slightly to calibrate, or this is what I have read). I tried the front element tightened down at various points along its possible rotation path, but the lens was still severely front-focusing (maximum AF fine adjustment in the K-5 menu was not able to solve the problem completely, but gets it fairly close at f/2.8. It could probably use an adjustment of -11 or -12, if it were possible)

So, I ordered a new lens. The new lens requires -9 AF fine adjustment, or almost the maximum possible of -10! Also, the new lens is less sharp (or less contrasty, I can't really tell) than my old lens when shot wide open using live view AF and self timer on a tripod. Is this two bad lenses or is my K-5 body messed up?

Also of note are the two lenses do not seem to have the exact same optical axis when mounted. Carefully mounting both copies so as not to disturb my set-up, the exact center of the image of my test target is in a slightly different spot in the frame when shot with each lens. This leads me to think my new lens and/or my old one is bad...

But, I also made some observations that lead me to think at least part of the problem is with my K-5 body: images of the target taken with both lenses are rotated about 1.25 degrees counter-clockwise. I was very careful to make sure both the target and camera were dead level before taking photos. Also, the center point of the image migrates slightly to the upper left of the frame as the lenses are zoomed in - this happens on both lenses. Is this normal? These results lead me to think that I have a misaligned image and or phase-detect sensor in my K-5 body. In addition, the images from both lenses appear softer on the left side.

So, do I have bad lenses, a bad body, or a combination of the two, and what do you think I should do? I must return the new lens very soon if I am to get a refund on it. Thanks, in advance, for your help!

~ Jon

P.S. My K-5 was purchased new from an authorized dealer and has just under 5000 clicks on the shutter, and I have taken very careful care of it (not that this precludes it from developing problems)

P.P.S My Tammy 90mm f/2.8 macro requires -5 AF fine adjustment on my K-5 at this point, but I have not tested it further yet.

P.P.P.S. Here are 100% crops of the old (self-repaired) lens and the new Tammy 17-50 that I just ordered:

Attached Images
 

Last edited by jon.partsch; 10-28-2018 at 08:52 PM. Reason: Add photo attachment
10-28-2018, 05:30 PM - 1 Like   #2
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The Tamron 17-50 just seems like it has poor QC. Mine severely front focuses and it has extremely bad barrel wobble with rubbing elements when at 17mm and close focusing. Mine however only cost me 20 dollars so I can hardly complain.

In your case I'd just look for the Sigma 17-50 as that seems to be more solid, or upgrade to the 16-85 from Pentax. The Tammy just doesn't hold up to any sort of abuse.
10-28-2018, 05:44 PM   #3
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QuoteOriginally posted by ZombieArmy Quote
The Tamron 17-50 just seems like it has poor QC. Mine severely front focuses and it has extremely bad barrel wobble with rubbing elements when at 17mm and close focusing. Mine however only cost me 20 dollars so I can hardly complain.

In your case I'd just look for the Sigma 17-50 as that seems to be more solid, or upgrade to the 16-85 from Pentax. The Tammy just doesn't hold up to any sort of abuse.
Thanks, ZombieArmy.

I appreciate this viewpoint. My concern is that the Sigma is more expensive and heavier. I am tight on cash, and with physical problems that I have, I am looking for the lightest kit possible. Also, I have heard that the IQ on the Tamron (good copy) easily exceeds the IQ of the Sigma (though I realize this is probably trivial in practice). Pentax options are out due to price and that I need to be able to work at F/2.8.
10-28-2018, 07:30 PM   #4
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Okay, I added some 100% crops of my tests at 50mm and f/2.8 to the original post above.

It's 100% obvious that, regardless of possible problems with my K-5 body, the new Tamron 17-50 that I ordered is complete junk. The performance of my old lens, even with slightly sub-optimal AF fine adjustment, should totally outperform the new lens.

I will return the new lens, hold on to the old lens, and hope for a K-3 iii soon to replace my K-5. I'm suspicious that my K-5 really does have some issues with the image sensor and/or phase-detect sensor.

Problem solved (sorta'). Still, I welcome any comments.

~ Jon

10-28-2018, 09:38 PM - 1 Like   #5
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I think returning it is the best course of action. The alternative would be to send it in to Tamron for service assuming it's covered by warranty. However, I had similar problems with my first copy of the 17-50 and two trips to the service centre did not fix it. I ended up selling that one for spares/ repair. I later got another which was bundled with a K-5 I bid on. That one was assembled in China rather than Vietnam or Japan and it works much better -- noticeably sharper in the corners and able to hit infinity at the wide end using AF (the old one would backfocus so much that it went beyond infinity meaning nothing was sharp within the frame). It is worth noting though that even the best copies seem to have some focus shift when you stop down so you may never get it dialed in precisely for all apertures and working distances.


If you need the 2.8 aperture though I might suggest avoiding this lens. While my good copy of the Tamron is usable wide open, it doesn't really excel until about f3.5. I also think the transmission (T-stop) isn't great. Nowadays for low light indoors I usually use my plastic fantastic DA 35 2.4 -- much lighter than the zoom and impressively sharp from wide open. To be honest, I still prefer my old 16-45 to the Tamron. while it's a nominally a stop slower, the Pentax lens is great wide open (above ~19mm: below this it's soft in the corners unless stopped down) and it is noticeably lighter, wider, has less distortion and vignetting -- and better colours.
01-27-2019, 12:19 AM   #6
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Conclusion: The new, made in Vietnam lens was sent back to B&H, and returning it was a breeze. B&H does have excellent customer service. I have done some work with the old lens, but haven't used it much in the last few months, and when I did, I focused in live view. I am in the process of purchasing a Sigma 17-50 HSM lens. I am hoping for an update to the K-3 line or a new crop sensor or full sensor MILC sooner rather than later, so I can upgrade from the K5.

~ Jon
02-15-2019, 05:52 PM - 1 Like   #7
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My 17-50 Tamron has been adjusted twice by Tamron and each time it has come back needing -10 on the K5. I did not send the body with the lens. Another sample I tried was also -10. Both had connectivity issues randomly on both my bodies, but Tamron fixed mine (I didn't try to have the other sample fixed.) So possibly -10-ish is just how Tamron adjusts the lens. I imagine they could do better if they had a body to adjust it on.

Your old lens looks like a good copy, and you did an excellent job of providing those test images. Mine is not great at f2.8. I'm not sure there is much performance difference between two good copies of the Tamron vs. the Sigma but I agree the Tamron is more physically appealing (smaller, smaller filter.) I only have a K5. I wonder if I bought a 24mp body I'd have to replace all my lenses, but I'm really discouraged by the difficulty of getting good copies (all brands including Pentax.)

I do have two K5 bodies which helps me eliminate body issues when evaluating lenses.
02-19-2019, 12:13 AM   #8
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QuoteOriginally posted by tibbitts Quote
My 17-50 Tamron has been adjusted twice by Tamron and each time it has come back needing -10 on the K5. I did not send the body with the lens. Another sample I tried was also -10. Both had connectivity issues randomly on both my bodies, but Tamron fixed mine (I didn't try to have the other sample fixed.) So possibly -10-ish is just how Tamron adjusts the lens. I imagine they could do better if they had a body to adjust it on.

Your old lens looks like a good copy, and you did an excellent job of providing those test images. Mine is not great at f2.8. I'm not sure there is much performance difference between two good copies of the Tamron vs. the Sigma but I agree the Tamron is more physically appealing (smaller, smaller filter.) I only have a K5. I wonder if I bought a 24mp body I'd have to replace all my lenses, but I'm really discouraged by the difficulty of getting good copies (all brands including Pentax.)

I do have two K5 bodies which helps me eliminate body issues when evaluating lenses.
tibbitts,

Thank you for this. I'm somewhat heartened to hear that your experience with this lens is similar to mine. I tested my copies wide open and different focal lengths, but this lens is known to be weakest (as is typical for zooms, I gather), wide open at it's longest focal length. The test comparison should best highlight the differences between copies at the focal length and aperture I presented. I don't have another body to test the lens on, so I can't determine if the -10 setting required is due to mis-adjustment of the lens or of the phase detection sensor in the body. I kinda' hate that focus adjustments that are always needed, and how hard it is to nail focus with the K5 in general, even after making these careful adjustments; not to mention that there is no way to adjust a zoom lens correctly for every focal length. I am longing for a great mirrorless option like Nikon, Canon, and Sony offer with sophisticated phase detection on the imaging sensor and/or great focus tracking. Those systems also have a much better selection of modern lenses available in the long focal lengths that a wildlife photographer like me needs. I am toying with the idea of jumping ship for Nikon, but waiting to see what Pentax releases this year first, and to see if there are any hints about Pentax joining the mirrorless revolution.

~ Jon

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