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03-15-2011, 05:53 AM   #1
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Experiences with Tamron 17-50mm or Sigma 18-50mm 2.8 Macro on K-5?

Ok, I know that these lenses are extensively compared here and elsewhere, but I am about to make a decision for one of these two lenses and I just want to know if anyone with a Pentax K-5 and a Tamron 17-50 (non VC) has experienced problems with the AF in low light as I have read multiple posts over at DPreview describing the AF inaccuracy in low light as the major drawback.

Thanks for helping!

03-15-2011, 06:40 AM   #2
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I have the K-r and the Tamron 17-50

The K-r also has the FF issue in low Tungsten light, I dont notice it in any other low-light myself. Otherwise it works great.

The Tamron 17-50 is also fantastic. Super sharp, nice quality lens and great price. My tamron focuses fine. I notice that the focus is a tiny bit off at the long end (which I dont really use anyways) could be the lens or my body not sure.

I would say though that unless you work in Tungsten low-light a lot it will be a non-issue. Plus there are some firmware fixes out there and on the way which can help the problem a little bit at least
03-15-2011, 08:34 AM   #3
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Thanks for your reply, but I am now even more confused... Just browsed the web some more for user reviews and the problems with AF in low light do not only happen with Pentax bodies, but also with Nikon or Canon.

And I am not buying an f2.8 lens to shoot in environments with plenty of light...

Problem is that the Sigma is not longer produced or sold in the Netherlands, so there is only one store left that has the Sigma in stock, but unfortunately that store does not have the Tamron in Pentax mount, so no side by side comparison is possible.
03-15-2011, 08:50 AM   #4
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QuoteOriginally posted by Lampo Quote
Just browsed the web some more for user reviews and the problems with AF in low light do not only happen with Pentax bodies, but also with Nikon or Canon.
Yes the fast wide angle zooms are especially tricky lenses to manufacture. You may be lucky with Tamron or Sigma and get great results. But there is a reason for the original lenses to be more expensive - they are more likely to AF accurately.
I only had experience with two 17-50 Tamrons (one great, one acceptable), Canon EF-S 17-55/2,8 (OK on 30D body, probably much better on 40D but I never tried) and one DA*16-50 (excellent once the AF microadjustment was set on K-5). I saw a Sigma 18-50/2,8 offered used for very good price but TBH I didn't even try to mount the lens on my camera when I met the seller saw it's condition. The lens barrel was shaky, focusing ring rubber fell off. He said it works fine but I still I couldn't use such atrocity of a lens. EX Sigmas are acceptable, but not regular DC ones...

03-15-2011, 08:53 AM   #5
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I have had low light FF problems with the Tamron 17-50 and K-5. My impression at this point is that these continue with FW 1.03, which made a marked difference for the DFA 100mm 1:2.8 so I'm puzzled. Then again it might be just the my particular copy; it could use a bit more than -10 of focus adjustment in daylight it seems. BF/FF complaints with this lens appear common enough to make it especially good idea to buy it new from reputable vendor so that a problematic copy can be exchanged / returned for refund. As such this seems like a fine lens worth recommending.
03-16-2011, 02:07 AM   #6
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Thanks for all your thoughts on this, I will check out the Sigma 18-50 2.8 EX DC Macro first, as it has a real good price that I can not ignore because of my budget restrictions. I will go to the store and check the lens before buying. If the lens fails to make decent images with f2.8 I will buy the Tamron in another store and check it out before I will buy it to see whether it has FF issues.
03-20-2011, 07:39 PM   #7
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I recently purchased a tamron 17-50 and I couldnt get a sharp pic at 2.8 on the long end. Do your copies offer sharp pics at 50mm @ 2.8? I tried indoor and outdoor lighting as Im still waiting on the firmware to fix my ff issues.
03-20-2011, 08:35 PM   #8
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I owned the Tamron 17-50 for 3 years and shot many thousands of shots with it on my K20d. The lens was excellent, focusing well in low light. This is not everyone's experience from what I read. My advice is to buy new, from a reputable dealer, & return it until you have a copy with which you're happy. I a good copy is gold!

Good Luck

The Sigma is an excellent choice too.


Last edited by Jewelltrail; 03-21-2011 at 10:57 AM.
03-21-2011, 06:14 AM   #9
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QuoteOriginally posted by mrjamesabels Quote
I recently purchased a tamron 17-50 and I couldnt get a sharp pic at 2.8 on the long end. Do your copies offer sharp pics at 50mm @ 2.8? I tried indoor and outdoor lighting as Im still waiting on the firmware to fix my ff issues.
Mine was also a bit off at the long end, although I used it at 17mm probably 98% of the time which was perfect
03-21-2011, 10:48 PM   #10
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QuoteOriginally posted by Deimos Quote
Mine was also a bit off at the long end, although I used it at 17mm probably 98% of the time which was perfect
Mine was spot on, throughout its range--amazing lens indeed.
03-22-2011, 07:00 PM   #11
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I just bought this lens and it arrived today. I haven't had a chance to thoroughly work it out yet, but so far from the simple tests I've done, mine looks like it's right on the money at 50mm @ f/2.8 and 17mm @ f/2.8. I'm going to test it in low light and I'll let you know what I find.
03-22-2011, 07:11 PM   #12
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Its possible mine was a tungsten or low light issue as well. I really didnt take too many shots at 50mm.
03-22-2011, 08:49 PM   #13
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After doing a little more testing, I'm still very pleased. In tungsten low light, the lens seems to lock on fine and is pretty accurate. At 50mm it did hunt a little bit, but I was in really poor lighting too. Seems to be acceptable for me anyway. Also did some tests at different focal lengths for FF and BF. Everything seems fine. At 17mm I may have had a very slight BF issue, but it could also be a poorly executed test. At any rate, it was very minimal and probably all the 17mm shooting I will do will be with a large DoF.

After one night of testing, I'd have to say I would definitely recommend this lens for low light.
10-07-2011, 06:06 PM   #14
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Tamy 17-50

I had this lens for several years. It had to be re-calibrated twice in 3 years. I sold it it as it was not a reliable lens. Pentax 17-70mm f4 as an replacement is not quite as sharp, but has better color and IS reliable. To each his own, but few people ever comment on long term performance.
10-08-2011, 09:36 AM   #15
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My wife has the 17-50 and there has been nothing to complain about - lovely lens on any Kxxx!

Just in another division, compared to the kit lens (no matter if you have the WR, or not)!

Last edited by Tord; 10-08-2011 at 11:21 AM.
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