To begin with, apparently, the "lottery" Tamron about the front-focus would not be a legend: the first copy I received was indeed afflicted with a pronounced forehead-focus, which exceeded the possibilities for correcting my Box (K II-5 is provided with a correction system AF). In short unusable unless one is as blind as a mole.
Fortunately Amazon replaced me the copy without question, and the second received was tip-top sounds spot, no correction required, all good.
I've tried this goal half journé and found it very enjoyable. Lightweight, easy to handle, and frankly for the price the optical quality is excellent. It deserves its good reputation. For the daytime and 90% of the photos, I do not see what would justify getting into ranges and prices.
The problem is that I am passionate night shot without the flash (concerts, night scenes of city life, various holidays ...), so I have long dreamed of a zoom "to do everything" brighter goal and Sigma did, I tried also the Sigma 18-35 f / 1.8 (careful I am not referring to the Sigma 18-50 - less bright - which is the "natural" competitor to the Tamron 17-50) .
I fell in love with the Sigma 18-55 ... much higher resolution, but hey, that without pixel-peeping, it does not make much difference in practice.
As against making a beautiful difference is:
- The gain in brightness of f / 2.8 to f / 1.8, it's more of a stop ... in night shooting that makes a nice difference, when you can stay at ISO 800 instead of up to 1600, it changes!
- Chromatic aberration, well below the Sigma 18-55. If your housing or your "dérawtiseur" preferred well corrects chromatic aberrations, no problemo. I for reasons too long to explain here it makes me a very foolish to have a zoom with almost 0 chromatic aberration.
Well now, the Sigma 18-55 is much more expensive, longer, and MUCH heavier, so the comparison is not very fair to poor Tamron honestly that fills his contract. Could not find better at this price. Some prefer the Sigma 18-50, not me. I tried it too. And then by comparing the two, I preferred the Tamron. It is the 18-55 f / 1.8 that attracted me in Sigma. If it did not exist, I would have adopted this Tamron and I think I would not have regretted.
