I Googled. Indeed a nice and compact lens. Just the compactness alone stands out, but so do the rendering. Prices are attractive as well.
A FE 85 f1.8 has somewhat to be bigger, but how big?
Then there's the AF question? Not an issue for me since an 85 I will always go manual for critical focus.
I will not need a super wide other than the 21 Distagon 2.8. The A7S would not be the typical choice for landscape, even I think it would do fairly well just because of the beautiful color tone.
A better FE 35mm would be on my wish list.
Contax G lenses are very nice : sharp, contrasty, light and compact. Originally, they were AF lenses and there is a Techart adapter allowing AF. But I find it quite tricky. You can put it in manual mode and the wheel is very smooth to turn. However I always forget the procedure to switch from AF to manual and then I was never able to get magnification to work. it is very slow to AF and often miss the focus. The Metabones adapter I have for Canon lenses works better. I have the Techart adapter version 2, but a version 3 has been released recently.
There are probably more silver barrels than black barrels available, in case you care for the color.
The best Contax G lens is the 45mm F2 IMO, then the 21mm F2.8, the 90mm F2.8. The 28mm and the 35mm weren't as well regarded. On the A7r, only the 45mm and the 90mm are good performers. The 21mm and 28mm produce bad corners (the rear element is standing too near of the sensor).
The main problem of these lenses is purple fringing, but this is correctable in LR.
Since the adapter is tricky, I tend to use the Tamron 90mm F2.8 macro instead of the Contax : it supports AF (although rather slow) and produces excellent corners, better than the Sony FE 70-200mm F4. The Tamron is also a very light lens, although bigger than the Contax G 90.
