Now the legendary Zeiss.
It is relatively heavy, which comes to meet me personally, because I prefer it that way.
The build quality is impeccable, albeit missing seals against dust and moisture are a small drawback.
So close in on the body, and out to take pictures. Immediately a big "Aha" effect - the autofocus is exorbitantly fast, ultra-quiet, and very precise. The quality of the photos are impressive throughout the entire zoom range. While you had to suffer significant loss of edge sharpness in at the Sigma, so here surprised the Zeiss lens. Distortions are (subjectively considered) only there if you look for that.
In theory, one can certainly complain about a few points, but that would be for me "nitpicking".
In the sum of its properties, the Zeiss 24-70 is absolutely convincing, the SSM is the best you can buy across brands, and so I think the rather high price as a perfectly adequate.
As a standard zoom to the 900 in my opinion a must. For APS-C area (I'm going to buy because of the weakness of the Lowlight 900 a a55 as a second Body) will be around something missing down, corresponds to it there just a 36-105.
Here is my summary:
++ Level of craftsmanship
++ Super Fast autofocus
++ Very quiet SSM
++ Very little distortion
++ Very good image quality at maximum aperture
++ Front lens does not rotate; thus not a problem for filter insert
- No sealing against dust and moisture