The LEICA SUMMICRON 90mm f/2 is 100% compatible with every LEICA M camera from the LEICA M3 of 1954 through today's LEICA M7, MP and the LEICA M9. It also came in screw mount.
Its performance is outstanding on film. It's very sharp when shot properly, especially wide-open at f/2, however if you're counting pixels on an M9, the sides are softer at the larger apertures. f/5.6 is optimum.
1.) The SUMMICRON 90mm f/2 was extremely popular in its day, so there are many of them available.
2.) It's heavy. When Leica came out with newer, smaller versions (the SUMMICRON-M and APO-SUMMICRON-M 90mm f/2 ASPH), shooters dumped these old SUMMICRON. Thus there is little demand for these among the truly Leica smitten.
3.) If you're counting pixels, this lens wants to be stopped down for best results. It looks fantastic on film wide-open, but if you're shooting flat test targets at larger apertures, other 90mm lenses are better at the sides on the M9.
To quote Leica's own sales material of its time (LEICA M5 sales brochure 110-87e, VI/75/DLX/w (1975)), this 90mm "at f/2 offers outstanding performance over the whole image field" and "Besides exceptional definition it offers high resolution and optimum image contrast."
Leica advertised it, along with the 35mm SUMMICRON and 50mm SUMMICRON as "the most advanced optics yet created by man."
If you want a great 90mm lens for your LEICA at a bargain price, this is it, especially if you get a beater. Beaters were lenses that were good enough to be carried by professionals day in and day out, so they are the good ones. Each of the beaters above performs exactly as well as the shiny silver one. Even if the lens has a small chip in its glass, that's a discount on price, and rarely on image quality.
The LEICA 90mm SUMMICRON was the world's reference for high performance, high speed teles for over twenty years. Newer teles are better under the microscope, but this bargain-priced lens can still create great images.
This SUMMICRON may no longer be the best from Leica, but its' still better than the Nikon 85mm f/1.4 AF-D shot on a Nikon D3X. I've compared them.
LEICA shooters don't waste time counting pixels. They just shoot.
Bokeh, the quality of out-of-focus areas as opposed to the degree of defocus, runs the range from fair to good.
f/2: fair; blur circles have brighter edges.
f/2.8: fair to neutral.
f/4: good.
f/5.6: neutral.
Here are crops from extremely enlarged prints of about 36 x 48 " (100 x 150cm), or the equivalent of looking at LEICA M9 images at 100% on-screen.
In these examples, a vertically polarized phase lattice was set up at 3 meters (10 feet) on which the SUMMICRON was focused, and the synthetic reference vegetation seen out of focus in the background was at 15 meters (50 feet).
As LEICA M lenses go, this is a big fat lens that handles great.
The only funny business is that different versions have aperture rings that go in different directions!
Look carefully: sometimes just the dot moves against a fixed scale (earlier versions), or the numbers move past an index on the newest version, just as today's lenses.
If the dot moves against a fixed scale, the numbers need to be in backwards order for the ring to move in the direction it usually does on most Leica lenses today.
Focus accuracy is a personal issue between your sample of body and your sample of lens.
If you're picky, it's very rare to find any combination of samples of rangefinder camera and long lens that give perfect results at every distance, every time.
The center is contrasty even at f/2, but resolution isn't as high. Sharpness improves at each stop, becoming optimum and really sharp at at f/5.6.
At f/2, the sides are less sharp. They improve as stopped down, becoming optimum, but never quite as sharp as the center, by f/5.6.
You're not going to see this unless you're shooting tests. Your biggest limitation to getting sharp results is how well the rangefinder of your sample of camera matches your sample of lens.
This beater Canadian 90mm f/2 is sharp at f/2, just as Leica's sales material claimed for it back when it was the best Leica had to sell.
I don't belive page 65 of today's "Leica M Lens Secrets," where the clever marketing people pull a rare double-switch and now claim that "Its performance at full aperture was moderate, so the ever-creative sales people invented the notion of a portrait lens."
In 1965, Leica described this lens' performance as "brilliant images with crisp edge-to-edge sharpness from f/2." (Leica lens brochure 11-34f, October 1964.)
