I'm cross-posting some of this text from another forum, so apologies to those who read it twice
I received my lens this week and had some time to shoot it yesterday. Prior to this, I owned the Sony 16-35/4 (sold in anticipation of the Tamron), and I currently own the Voigtlander 15/4.5 III and Sony 28/2 for this range. For practical purposes regarding handling and usage, the Tamron is almost exactly the same size and weight as the two primes put together. Both setups feel small and light! There is an advantage to having two lenses in that I often carry just the Sony 28/2 as a walk-around lens. Or I can skip the 28/2 and carry the Voigtlander 15mm with my Voigtlander 40mm (sharing the same filters too). Whether I will sell these primes and stick with the Tamron, I haven't decided yet.
I compared shots of the two primes against the Tamron and tested the Tamron corners for centering. Mine is well centered, at least testing the extreme focal lengths, 17 and 28.
Between the Tamron and my CV15, you'd be hard pressed to tell them apart aside from the focal length difference. Wide open for both lenses (f2.8 vs. f4.5), the CV15 is just a bit better. Stopped down, there's not really much difference to talk about, but the Voigtlander has more CA. My CV15 has great corners, no smearing.
Against the Sony 28/2, I found the Tamron was better resolving at both f2.8 and f8. Most of the difference is in midfield and edge/corner resolution. Both lenses look good in the center. Bokeh-wise, compared at f2.8 the Tamron is a bit cleaner, but the Sony of course has f2. I would say 95% of my Sony 28/2 shots are family shots at f2 where center sharpness on the Sony is great. There's a bokeh comparison below, and I think the difference is small enough not to matter to me. For environmental portraits with maximum bokeh, I have the Voigtlander 40/1.2. The Tamron does focus more closely than the 28/2 by the way. Overall, I would say that I feel like the Tamron can pretty much replace everything the 28/2 does except for its size. For a look at bokeh--a quick comparison wide open between the Tamron at f2.8 and the Sony 28/2 at f2 with full-size links below (keep in mind there's no profile applied to the Tamron). Don't read too much into the colors, since I've adjusted both quite a bit:
Tamron at 28mm f2.8 by
Graham Gibson, on Flickr
Full-size:
https://live.staticflickr.com/65535/48439241986_a961b1806e_o.jpg
Sony 28mm at f2 by
Graham Gibson, on Flickr
Full-size:
https://live.staticflickr.com/65535/48439390032_277b876c27_o.jpg
And a few more shots--Tamron at 17mm, f2.8:
Cactus by
Graham Gibson, on Flickr
Tamron at 28mm, f2.8:
Bokeh test by
Graham Gibson, on Flickr
Tamron at 28mm, f2.8:
Bokeh Test by
Graham Gibson, on Flickr
Tamron at 17mm f2.8:
Close focus wide angle by
Graham Gibson, on Flickr
Tamron at 20mm at f22 (this was actually using Sky HDR, I forget what exposure was used for the sky):
Orinda Hills by
Graham Gibson, on Flickr
Tamron at 17mm at f13, Sunstar:
Sunstar by
Graham Gibson, on Flickr