I used to use Rollei 3003's and had a set of Zeiss lenses. I can't say how they'd do on a digital sensor but they were excellent on film.
There's a 25 f2.8 Distagon, 18 f4 Distagon and 15 Distagon. I can't remember the speed of the 15 but think it was f3.5 but could have been 2.8. I owned them for several years. The 25 was I think made in Singapore but the others were German.
I have the Nikkor 20 f3.5, the little one with 52mm filters. I use it on my DF and use it quite a bit. As 20's go from Nikon it's good. Wide open it's a little soft in the corners but really good in the center. At f8 it's really good overall. I'm very fond of it.
I owned the 20 f2.8 in the film days and it was quite good. I've also used the old 20 f3.5 that uses 72mm filters. My experience was on film and can't confirm on digital. It's just OK and nothing special. 20's haven't been Nikons strong point in those days. I don't think the 18's were either or the 15 f3.5. I had a 15 f3.5 and shot a lot of annual report and editorial work with it but had to be conciliatory all the time of flare and light sources just outside the frame. Matter of fact if any light source could hit the lens you would get big time flare. The one positive thing was it's pretty sharp, really great perspective and if you're creative could use the flare to your advantage.
I traded the 15 for the AF 14 which was a huge improvement in flare.
About 35 years ago I used Pentax MX in my work. Loved the bodies and most of the lenses with one e. Eption. The 18mm f3.5 was the worst lens I've ever owned. I had three copies and sent one back to the factory for adjustment twice. It was good in the center 1/3 and as you approached the edges it turned to smeared mush. All three lenses were the same. I don't think it was made for long.
Pentax took my 18 back and I got a sweet little 20 which was a jewel. The was in the 70's if that helps date the lens.
I understand th Zeiss 25 Flektagon is very good but never used one.
There's always the new Zeiss lenses in EOS mount. I tried a 25 f2, 35 f2 and 100 macro f2.when I bought my D800. I know people that swear by them especially the 21 but the three I had weren't anything special wide open at the outer 1/3. I felt my vintage Nikkors were as good. I wound up returning them to B&H.
