The Carl Zeiss Distagon 2.8/21mm ZE T*(red)
I've owned my 21mm Distagon for about ten years now. It's in Canon mount so with my Metabones adapter I get electronic aperture control but of course it is manual focus only. On Canon cameras it will give you an indicator when you hit optimum focus though that doesn't carry over when adapted onto my A7RII.
This lens is probably the most expensive lens I own. Can't remember purchasing anything else that cost in the $1800 range as this was when it was purchased new. Which clearly indicates I haven't ever bought any new or even very good old Leica lenses other than the one 50mm Summicron R I purchased specifically because it was the only way I could afford a Leica Summicron lens. R lenses being SLR lenses rather than Rangefinder and not bringing nearly what the rangefinder Leica lenses do. Heck, I even have a Carl Zeiss C Sonnar 1.5/50mm ZM T*(red) on my pristine and rare serial number Leica M3 because I simply can't afford an equally nice Summicron to match with the M3. But now I've rambled a bit as I'm wan't to do.
The Zeiss 21mm Distagon is definitely a beast. Very heavy. Almost as heavy as my brass Nikkor-P.C(red) 1:2 f=8.5cm, which is like a little lump of lead. The Zeiss 21mm is so heavy, unbalanced front heavy from the grand front element that I've dropped this lens twice on the pavement. Both times in San Francisco due to me being in a hurry and the unbalanced weight flipping it out -- once from my hand and another time out of a partially unzipped compartment in my bag. Smack! Down on the pavement causing me to stop breathing until confirming it still appeared to be a working lens. Which it was/is save for several scratches. Which means I was lucky it didn't fall on my foot or ankle!
Now I'll spare you more of my run on and since I've already plagiarized Ken Rockwell for the excellent pic above which goes with a wonderfully humorous and insightful review he's written, I'll simply point you to his page on this great lens for all the skinny.