[Klaus]

Good with a few caveats

https://www.opticallimits.com/sonyalphaff/1174-sigma2870f28dn

[Rover]

Kind of predictable given the positioning. I remember nearly buying the old DSLR 28-70/2.8 by Sigma back in the day - there was a huge amount of various "midrange" offerings from them in that time (2005ish), though they would all probably be considered appalling now. I ended up with the Minolta 28-75 then, though (a rebadged Tamron, of course).

By the way, the lens isn't in the master list of reviews on the Sony page?

[Klaus]

It seems that many of these std zoom lenses follow a similar pattern - being rather weak at 70mm.

[Rover]

Same deal as with the wide angle zooms like 12-24 / 16-35mm almost invariably being weakest at the long end... sometimes atrociously so.
Maybe the producers are thinking most users have something with overlapping, or at least adjacent zoom range (70-200 in case of the standard zoom, 24-70 in case of the wide zoom). Which is a little unfair (in theory - I don't think I've ever noticed any such weakness in practice) to those who prefer to have a gap, using the 16-35 + 70-200 or 24-70 + 100-400 combos, or even 16-35 + 100-400 like I do most of the time.

[fotorrhoe]

It seems that many of these std zoom lenses follow a similar pattern - being rather weak at 70mm.

Therefore I look for a test of the Tamron 20-40/2.8  that avoids this FL and complements quite well with the 70-180/2.8 for a lightweight and flexible Duo.

[Rover]

The 20-40 will probably be good at 20 and 28, and tank at 40. Though by how much if, of course, the million dollar (or rather, $800?) question.

[Klaus]

A 20-40mm is hardly a standard zoom lens.

Sony's 20-70mm is, though ...

I thought of reviewing the Tammy, but I'm not sure about the point of this lens anymore, given the existence of the Sony lens.
Locally, the Tammy goes for 1100AUD vs 1500AUD for the Sony so there's not a hell of a lot between them.
However, this may be different in your part of the world.

[Rover]

I say review a coke bottle if you can get your hands in it and have the time. But it's easy for me to say, of course...

I know I have a knack for using strange lenses. I was ridiculed by a gearhead / measurebator colleague for being seen with the Canon 24-85 mounted on the Z9 ("what next, you'll put a window glass on the camera?"). Admittedly I deliberately put it on visibly, to troll him for his insufferable attitude, but the lens makes good pictures so I'm not just keeping it for giggles, far from it.