Tony is that the pre-asph you have? Those I see for around a grand. Or is it the ASPH, which fetches close to 2k?
I think you have a good question, very interesting really.
Here is Puts on what I think is your version, the pre-asph:
"The general performance of the Elmarit-M lens is better than that of the Super-Angulon at f/3.4. This is partly due to the reduction of astigmatism, which results in improved rendition of fine details.
At f/4.0 extremely fine details are vis- ible with good contrast in the center and within a 12 mm diameter circle around the center. From there to the corners the image details become progressively softer, but fine details remain within a detectable range.
Optimum performance is reached at f/ 5.6 with extremely fine details now vis- ible over the entire image area into the outermost corners. Subject outlines, es- pecially in the outer zones, have soft edges, giving an overall impression of a smooth, somewhat subdued image. Stopping down to f/11 and smaller aper- tures diminishes image quality. Decentering was not measurable.
Generally speaking, this lens is a com- mendable performer and an improve- ment over the Super-Angulon lens. In the field at the wider apertures, image quality is a bit modest."
Now here he is talking about the ASPH:
"The overall image quality is a quantum leap forward in relation to all previous 21mm lenses in the Leica stable.
To place it in perspective: the perform- ance at f/2.8 is better in all respects than that of the f/3.4 Super-Angulon at f/ 5.6.
At f/4 contrast and the clear rendition of very fine details improve, with the corners still lagging a bit behind. Overall contrast is now at its optimum, with ex- ceptional performance over a large part of the image field. At f/5.6 overall con- trast drops a little, but very fine details are still crisp into the far outer zones.
From f/8 the performance drops ever so slightly and at f/16 it is noticeably be- low optimum.
Decentering is not measurable. Overall assessment: this lens produces out- standing image quality at full aperture, which continues to improve as it is stopped down as far as f/8.
It is by far the best 21mm lens in Leica history and the only recommended choice for the person who needs supe- rior performance from a 21 mm lens starting at f/2.8."
Check out the charts:
Leica 21/2.8 pre-asph by
unoh7, on Flickr
Leica 21/2.8 ASPH by
unoh7, on Flickr
Huge difference really. Puts makes an intriguing observation which may point to the absolute supremacy of the SEM 21:
"The performance of extremely wide- angle lenses at infinity is sometimes discussed as if it were a bit below expectation when compared to lenses with smaller angles of view. As I always use the same scene for a comparison, I was able to compare the image quality of a distant scene as recorded with a 28mm Elmarit-M lens (latest generation and a superb representative of its kind). The 28mm produces a high-contrast image, with extremely fine details, ren- dered very crisply. The overall image also has a clarity and lucidity that is diffi- cult to quantify.
In direct comparison, 21mm lenses are softer, they lack the overall clarity and crisp reproduction of very fine de- tails. The same amount of details as obtained with 28mm lenses can be noticed without difficulty, but image de- tails are slightly ‘fuzzier’.
Optical progress can easily be fol- lowed in the discussion that follows, with the 21 mm f/2.8 Elmarit-M ASPH representing a very high level of progress. It is the only 21 mm lens that compares favorably with the 28mm f/ 2.8 Elmarit-M."
I can tell you the SEM 21, like the ZM18, takes this another step with jaw dropping performance at infinty. Here is Puts on the SEM 21, which is one of his three favorite Leica lenses: "The Super-Elmar-M 21mm f/3.4 ASPH. approaches the ideal lens design: one does not often encounter a high-performance optical cell with homogeneous image quality at all apertures, distance settings and image height from centre to 21.6 mm wrapped up in a compact high-quality precision mount, even in the Leica stable."
But all that may be moot for you and your taste, and many others as well. You mention a zeiss characteristic "cold and clinical" and I think one might well observe the zeiss color signature as slightly cooler than Leica, but for all the rest, it's case by case, with great variation in performance between say, a contax g 45/2 and a ZM 50/2, etc. Both very crisp, but very very different render, especially at speed.
You love your elmarit, and who is to say you should not? Especially on an RD-1, where the outer field is absent, the pre-asph is going to do very very well.