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11-28-2009, 06:20 PM   #1
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K-7 vs Tamron 17-50mm and Tamron 28-75mm

Hello everyone!
I'm opening this thread hoping to find some answers to my questions, but also maybe it'll be useful for other K-7 owners.
I owned a Tamron 17-50mm and I found that on my K-7 body all images are front focused using the AF (I described the problem here).
After 30 days of waiting for a solution from the service, I went to the store and they decided to replace the lens with another copy. They tested the new one on my camera, but we discovered the exact same front focus values. They repeated the tests with all new copies they had in stock (6 pieces), but with the same result. I asked them to test with another Tamron lens type, the 28-75mm F/2.8, but unfortunately the big front focus was still present on all (3 pieces). It was so big that we didn't managed to compensate it in AF Adjustment menu.
Sad moment for me because I love the Tamron 17-50mm IQ & sharpness and I was also thinking that my camera is the source of the problem. Maybe it is...
Anyway, they gave my money back so I went to the local Pentax distributor and tried a DA* 16-50mm. And guess what? With this this lens my K-7 is focusing perfectly even in low light/poor contrast situations.
So now I own a brand new DA* 16-50mm (and I hope without any already reported issues on this forum), but being just a hobbyist & novice photographer I have now more unanswered questions:
Are there any K-7 owners that discovered the same focus issues with Tamron 17-50mm and/or 28-75mm lenses, or I am the only one on the planet?
I don't understand why all my Pentax (DA 18-55 WR, DA 50-200 WR, DA* 16-50) and Tamron (90mm F/2.8) lenses is focusing perfectly on my K-7 body, but the Tamron 17-50mm & 28-75mm don't. Can anyone give me a reasonable explanation for this?
Is it possible that K-7 has a compatibility problem with Tamron chipsets in those lenses?
To mention that I've installed the latest firmware available for K-7 a few days before I bought the Tamron lens, so I cannot tell if the AF issue is somehow related with this firmware release.
Thank you in advance.
PS - Please excuse me for my pretty bad English, it's not my native language and I don't use it very often.

11-28-2009, 06:28 PM   #2
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It isn't just the K-7. Do a quick google search for "Tamron 17-50 front focusing" or "Tamron 17-50 front focusing nikon/canon" and you'll get a slew of reported issues from an assortment of cameras and systems.
11-28-2009, 06:54 PM   #3
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Thank you for answer.
Yes, I've already googled before buying the lens and when I sent my lens to service and I found a lot of reports about focusing issues of this Tamron model. But everyone is telling that after 2-3-4 replacements they finally found some good copies or they get their lenses repaired.
It is hard for me to think that I've got the chance to put my hands only on bad copies. There was 6 copies of 17-50mm and 3 copies of 28-75mm tested on my K-7 body with the exact same front focus values/results. Statistically it is almost impossible. Or my luck has completely gone... It seems it's not the case with all my other lenses, thank God
11-28-2009, 08:14 PM   #4
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Is 17-28mm at f/2.8 really necessary? I also have the Tamron 28-75 and I've been thinking that to cover the gap between my 10-20 and 28-75 I should get the DA 16-45 instead.

edit: I noticed that you just got the 16-50 instead... congrats I think the BF/FF problem common with third party is a side effect of the reverse engineering... I got a perfect 28-75 on first try though.

11-29-2009, 01:35 AM   #5
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My Tamron 17-50 must be a "good one" since it is knife-edge sharp and never focus issues.

I have heard far more positive reviews and examples from this lens than negative.

Jason
11-29-2009, 05:52 AM   #6
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QuoteOriginally posted by Andi Lo Quote
Is 17-28mm at f/2.8 really necessary? I also have the Tamron 28-75 and I've been thinking that to cover the gap between my 10-20 and 28-75 I should get the DA 16-45 instead.
edit: I noticed that you just got the 16-50 instead... congrats I think the BF/FF problem common with third party is a side effect of the reverse engineering... I got a perfect 28-75 on first try though.
Yes. for me the 16/17-28mm focal range is important, especially when shoting indoors, in low light and small places, but it is good also for outdoors. It gives you more space for your creativity. Don't forget we have APS-C sensors in our Pentaxes, which has a 1.5x multiplication factor, so we're talking about a 24-42 focal range in fact.
Those two Tamrons (17-50 & 28-75) are very good lenses, that's why I first tired them first. Well, the price was another reason
Glad to hear that your Tammy 28-75 is a good one just out of the box, this is what I hoped for mine. I'm just curious, have you tried it on a K-7 body? On mine it doesn't focus properly and as I've said, many copies were tested.
QuoteOriginally posted by Jasvox Quote
My Tamron 17-50 must be a "good one" since it is knife-edge sharp and never focus issues.
I have heard far more positive reviews and examples from this lens than negative.
Jason
Same here Jason, that's why i bought it. On MF this 17-50 lens really is a piece of jewelry. But it seems that the K-7 body has something against this lens using the AF system. At least mine, so this is what I'm trying to find out.
Is it my specific K-7 body, or it is a general K-7 issue?
And if it's my K-7 body the guilty one, why it doesn't produce the same error with all my other lenses, including a Tamron 90mm?
Can anyone bring some light in my confusion?
11-29-2009, 09:33 AM   #7
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QuoteOriginally posted by pkata Quote
I'm just curious, have you tried it on a K-7 body? On mine it doesn't focus properly and as I've said, many copies were tested.
Same here Jason, that's why i bought it.
I haven't tried it on a K-7 since I dont own it yet... but my K10D does backfocus it a bit, although I've fixed that with the debug mode. My other lenses that focuses perfectly on K100d also backfocuses similar amount on the same K10d though, so rather than lens I think it's the K10d in my case.
11-29-2009, 11:17 AM   #8
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Thank you Andi for sharing your experience. Because this K-7 is my only camera I own for the moment, I didn't had the chance to test the Tamron lenses on another body. Before K-7, I owned a Fujifilm S6500fd, so I'm new to the DSLR world.
After all the readings I've done on the Internet and all the tests done by me and by the professionals in service, I came to the same conclusion: the problem is in the body. It's hardly to admit that all 9 Tamron lenses tested (six 17-50mm copies and three 28-75mm copies) could give the exact same amount of front focus on the same body due to a lens problem.
Now I hope that more K-7 owners which already have this Tammy 17-50mm (or 28-75mm) in their bags, or at least have tested it on K-7 will share their opinion, to help me find if this is an issue affecting my K-7 body only, or it can be extended to a production batch, let's say launched between two dates, or even to all K-7 bodies.
Now I'm thinking to write an email to Pentax, maybe they will be so kind to put the K-7 in test with Tamron lenses and, who knows, maybe they will discover some new bug in the firmware or some hardware incompatibilities.

11-29-2009, 01:56 PM   #9
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Hi Guys, I have a Tamron 17-50 on my GX 20 and it focuses fine at 17 and at 50 with some slight front focusing at 35. Now after going through and researching the possible whys... I believe it has to do with the engineering, and manufacturing process. The specs that Pentax and Samsing have to work with are 110% accurate while Tamron and Sigma's are about 99%. I will be sending my lens into the service center to have them calibrated and then it's all golden from there on. I hope this helps!
11-29-2009, 02:46 PM   #10
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Yes, this might be one reason, keeping in mind that the Tamron lenses I've tried were released years before the K-7 body.
Oh, I hope that Pentax did not changed something in their engineering and those previously released third-party lenses are not fully supported anymore.
But because Pentax didn't said anything like this, I think this is not the case here.
11-29-2009, 03:26 PM   #11
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Sorry pkata, I did not mean that there is an incompatibility, but rather, there is a small discrepancy in tolerances in manufacturing. and in addition, the Tamrons and Sigmas are made for many different brands, Nikons, Canons, Sony, and Pentax to name a few :-).
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