These reviews are from long time Leica shooter, Mr. Alfred Breull.
The Summar is Leitz's first f 2.0 lens, introduced in 1933. It shows it's best results between f 3.2 and 6.3. In this range, it is comparably sharp, like my Kodak Retina Ia 3.5/50 mm Xenar from the 50ies. In this range, it is a "high contrast lens", but different than we use the phrase today. Here it means, that the lens shows clear colors but hardly shadow details. To give an example: When you look at a tree at dawn or sunset, you clearly see the colors of the bright parts, but the shadows are gone and almost black. That's what the lens does, even in bright daylight. Additionally, the unsharp areas are more unsharp than in a "usual" 50 mm, almost like from the 2/90 mm M Summicron. Both effects (suppression of shadow details and "increased" unsharpness) result in the most impressive 3D or pictoral effect I've ever seen from a 50 mm, incl Noctilux. The highlights are over-pronounced, which gives an additional impression of light in your pictures (like in impressionism). At f 2.0 the corners tend to be dark and the colors are almost gone. It is a warm to neutral lens.
The Summitar is Leitz's second f 2.0 lens, introduced in 1939. There are uncoated and coated versions. In my experience, both appr. agree in their rendition. It shows it's best results between f 2.0 and f 4.0/ 4.5, but you may use it up to f 8 or f 9. It is more sharp than the Summar, and it's sharpness is comparable to the 2/50 coll Summicron or between the coll Summicron and the rigid chrome Summicron. At f 2.0 the Summar's dark corners are gone. The unsharpness compares to the rigid chrome Summicron. The color rendition is (far) more rich than from the Summar, comparable to the 1.5/50 Summarit or even the rigid chrome Summicron (but less than strong than in the coll Summicron). At low light (1/60 at f 2.0, E 100s), the color impression changes from saturated to transparent (like thin water colors in painting). There are many shadow details, but far far less than in the current 50 mm Summicron. The 3D effect compares to the rigid chrome Summicron (less strong than in the coll Summicron), but is significantly less strong compared to the Summar. It is a "cold" lens.
2/50 coll Summicron:
The coll Summicron was introduced in 1953 (1954 M version). There are at least 2 versions, maybe 3 (if you count different coatings as different versions). The first (usually below s/n 1 mio) has a high(-er) amount of rare earth included in the glass melting process, and was described by Marvin Moss 2, 3 months ago. If you look thru the lens, the glass appears slightly yellow ("yellow glass" Summicron). The pictures are a little more warm than from the other versions (Viewfinder article). The second, which I know, has a "blue" coating, which "peels off" after long year's claening, and was decribed by Marc J Small recently. The glass is not yellow anymore. The third version has a coating which looks like "reflecting light" or like a mirror if you look from the side, and yellow if you look from above (this lens is sometimes also described as "yellow glass" Summicron). I know nr 2 and 3 from experience. They show best results between f 2 and 5.6, and the optimum at f 4.0. Although they are "somehow" sharp at f 8, I often have wished, I had another lens mounted at this f-stop. In my impression, they are a (very) little less sharp than the 2/50 Summitar, but have a very beautiful out-of-focus rendition (strongly modeled, but less strong than from the Summar). The colors are very saturated, almost as strong as in the current Summicron (at daylight at or above f 4 and 1/250, E100s). They are more strong than from the rigid chrome Summicron in sun shine, but less strong than in pictures from the rigid chrome Summicron after rain. In general, the lens has a "soft" sharpness and saturated colors. It's a warm to neutral lens.
Rigid chrome 2/50 M Summicron:
The rigid chrome M Summicron was introduced in 1956, and is identical to the NF Summicron (Erwin Puts). There are two different coatings: The first goes off after (long years) cleaning, and the front element looks grey; the second is blue to blue-violett and stays untouched. The lens shows its best results between f 2 and f 8, with an optimum at f 4. It's sharpness is so impressing, that I feel it as comparable to the current Summicron at f 4 or f 8. It is definitely more soft at f 2.0 or f 2.8, specially in the corners, but it's a "pleasant unsharpness", like the 1/50 Noctilux at f 2.8. Different, I don't like it's sharpness at f 11 or 16 (it's like the coll Summciron at f 8), because the loss of sharpness between f 8 and f 11 is too strong. The out-of-focus rendition is soft and pleasant, and tends more to the Summitar, specially in lower f-stops (f 2.8 to f 4), than to the coll Summicron. The modeling effect is less strong than from the coll Summicron. The color and grey tone rendition is very rich, specially in daylight up to (max) f 4, 1/250, E100s. The color saturation depends on the type of pictures: In lower light (1/60, f 4, E100s) the colors are very saturated, the shades are very rich; in bright sun light (above f 4, 1/250 E100s), the lens looses it's magic and is as fine as the Summitar or Summarit. It is my "one and only" 50 mm lens for rainy or strongly overcast days (if I look for color richness), and in b/w up to f 4, 1/250, 200 ASA (if I look for richness in grey tone rendition). The lens is a "cold", low to middle contrast lens.
Black 2/50 Summicron:
The "black" Summicron was introduced in 1969, and is - according to Laney - the officially 2nd version (thanks to i.e. Erwin Puts, we know better). I had this lens for some month, about 25 years ago, and I can give you my reasons why we "divorced" pretty soon - although you may call me something like a Summicron manic. Compared to the rigid chrome Summicron, my lens had an increased contrast but a reduced sharpness. The contrast agreed to the current 1.4/50 M Summilux, and the sharpness to the 2/50 coll Summicron. Maybe I had a "Monday production", maybe not. I was so disappointed by this lens at that time (in comparison to the rigid chrome Summicron), that I sold her pretty soon. In my memory (which may be errorous), the color rendition is comparable to the coll Summicron resulting from the enhanced contrast. Today, I'm sure, that I over-reacted 25 years ago, and that my expectations resulting from the rigid chrome Summicron (which I had sold to purchase the black Summicron) were too high. On the other side, I've never touched this type of lens again.
Current 2/50 Summicron:
The current Summicron was introduced in 1980. I bought it last year after reading Erwin Puts comments, which says in short: "simply the best". Whatever Erwin says on his site or in his recent Summicron evaluation and comparison, also agrees to my impression. The lens is astonishing sharp at f 2.0, and very sharp above. The color saturation is extraordinary rich, and the contrast is high. - But, it is not "my" Summicron (I sold it after half a year). For me, the color saturation in combination with it's high contrast was too strong, in all types of light, it reminds me on colors of children sweets (i.e. "Smarties" or "Easter eggs"). Additionally, I missed the rigid chrome's softness in the out-of-focus areas and the richness in grey tones. In my mind, and maybe depending on my type of film-development-print-paper-combination, the contrast in the grey tones is too strong. To give an example: If you have a soft/ tender (?, phrase) subject, like a landscape in fog, you need to underexpose the b/w film at least 1/2 or one f-stop with this lens to get a negative, which's print agree to your memory from the scene. The rigid chrome Summicron gives a correct negative without correction. The lens is a neutral, high contrast lens.
The Summarit was introduced in 1949 (M 1954), and is a coated Xenon (1936). It shows it's best performance between f 1.5 and f 4, with an optimum at f 2.8, but you may use it up to f 8 with fine results. It's sharpness is better than from the coll Summicron, if contrasts are not extremely large, and comparable to the 1-st version 2/90 M Summicron at f 2.8. It's out-of-focus rendition is soft to very soft, specially at lower f-stops (up to f 4). As in the Summar or in the rigid chrome Summicron, far out-of-focus light sources are shown as circles, whose outer borders are more bright than the center. The color rendition is a little "flat" (less saturated) in low light conditon, like from the Summitar at f 2.0, and less saturated than from the rigid chrome Summicron. Different, the color rendition is very fine, and almost as good as in the rigid chrome Summicron, when you have a little sun shine in your pictures. It's a very nice lens for 50 mm portraits, also from today's view. It's weak part are very high contrasts at low f-stops (f 1.5 to 2.8). It's a neutral lens with a very slight tendency to "warm".
1.4/50 M Summilux:
The Summilux was introduced in 1959, and there are 2 versions (2-nd, 1961). There are indications, that the coating has been changed around 1980; I have experiences with a 1981 lens. It's sharpness is comparable to the 2/50 R Summicron, 1-st version, which is slightly better than the 2/90 M Summicron, 1-st version. It's out-of-focus rendition also agrees to the 2/50 R Summicron, 1-st version. Color rendition is rich and saturated with lots of shades, and agrees to the visual impression. I see the most remarkable difference to the 1.5/50 M Summarit in the color and contrast management at lower f-stops under low light conditon: While the Summarit may produce "flat" or "thin" colors between f 1.5 and f 2.0 in very low light, the Summilux still shows saturated (and remarkable sharp) pictures. It's contrast is higher than in the rigid chrome or 2/50 R Summicron (1-st version), but still pleasant (in my perception). It's a "warm" lens.
The 1.0 Noctilux was introduced in 1976 (1.2/50 in 1966); there are indications, that the coating has been changed in the early 80ies. I have (some) experiences with a 1981 lens. You may use it between f 1.0 and f 8, with astonishing results at f 8 (for a f 1.0-lens). I prefer the lens between f 2.8 and f 4.0. At f 2.8, the sharpness is lower than from the 1.5/50 Summarit, maybe comparable to the 2/90 M Summicron (1-st version) at f 2.0 or a 1981 2/90 R Summicron at f 2.0. It's out-of-focus rendition is soft to very soft and modeled, maybe as "creamy" as in the 2/90 M Summicron. Unfortunately I've never had a result like Tina's b/w "Mesquito Indian Man"; my own experiences at f 1.0 compare to well-known LUG members' pictures on various web sites. To me, it's most remarkable performance is based in the lens' management of (light) contrasts: no matter how strong, the lens can handle it. The color management, specially at f 2.8 or f 4.0, reminds more on the 2/90 M Summicron than on any 50 mm lens. It's a neutral to "warm" lens with a tendency to white-yellow.
2/35 M Summicron:
The 35 Summicron was introduced in 1958; there are at least 4 versions (1958, 1969, 1973, 1980). I have experiences with nr 2 and 4, I prefer nr 4 (although nr 2 was a remarkable lens already). The lens shows its best results between f 2.0 and f 8, and it's hard to define an optimum f-stop (which is theoretically at f 4.0). Already at f 2.0 the lens shows remarkable sharpness, and you have the impression that you just change the DOF (and not the sharpness) when you decide for a higher f-stop. Later you find out, that the lens is indeed more sharp, i.e. at f 4.0, but you are so impressed by the total of it's rendition at f 2.0, that you hardly realize the increase in sharpness at a first glance. The sharpness is continuous between 1 m and infinity, and at least one class better than in the 2/35 Nikkor with floating elements (nr 2 is appr equal to the Nikkor). It's out-of-focus rendition is soft (and beautiful), and almost as strong modeled as from the coll 2/50 Summicron. The color rendition compares to the 2/50 R Summicron (1-st version) or 2/90 R Summicron (mine is from 1981), rich in shades; the lens is able to handle even large contrasts (light and color) without problems, but different than the Noctilux. While the Noctilux seems to reduce or adapt strong light sources to its own standards, the 2/35 Summicron shows both, the brightness of the strong light and unchanged (not influenced) colors in areas which are very close to the strong light source (i.e. reflections of bright sun in water, and the color of the water around the reflections). It's performance in low light is remarkable with a tendencey to white-blue. It's a cold lens.
2/35 asph Summicron:
I've not used this lens, but I saw print film results (Fuji-something, no Ciba- or Digiprint) from pictures Ferdinand sent to me. From what I see in the pictures, the asph 2/35 Summicron compares to the nr 4 2/35 Summicron, except that the lens is as sharp as the 1.4/35 ASPH Summilux between f 2.0 and f 4.0. The out-of-focus redition is as beautiful as from the nr 4 version (2/35), except that it's more contrasty.
1.4/35 ASPH Summilux:
The ASPH version was introduced in 1994 (1990, "aspherical"); mine is from 1996 and belongs to an M6 ESL. Different than the first version, this lens' glass is pressed and has 1 asph surface (first: polished, 2 asph surfaces). It shows it's best results between f 1.4 and 5.6, and between 0.7 and 10, 15 meters. I've never seen any 35 mm lens, which is as sharp as this lens, even at f 1.4. The rendition of the out-of-focus area is less pleasant, and rather disappointing to me in comparison to the 4-th version 2/35 Summicron's rendition (when I bought the camera/lens, I bought it becasue I was highly attracted by it's design and shape - I'm still attracted, but ...). To me, the out-of-focus rendition looks rather like a collection of colored/ painted corns than a 3D or pictoral rendition of the unsharp (fore- and background) areas. The richness in color rendition is equally impressing as the shrapness of the lens, specially in low and very low light (i.e. between f 1.4, 1/15, to f 2.8, 1/60, E100s). In my experience you need a slide filme to really appreciate, what this lens does with low light colors (a print film can't handle it). Above f 5.6, and at infinity (all f-stops) my 2/35 Summcron (nr 4) was more sharp. The lens is a high contrast lens; it's a neutral lens.
The lens was introduced in 1965; there are at least 4 versions (1965, 1972, 1979, 1993). I had an early version, maybe nr 1 or 2. Though it was remarkable at close distances, it was unsharp above 10 meters. I sold it, and purchased a 3.4/21 SA. Recently, I saw b/w pictures taken with a later version. The lens' rendition was very impressive, but I've no own experiences.
3.4/21 Super Angulon:
The 3.4 SA was introduced in 1963 and followed the 4/21 SA (1958). It shows its best results between f 4.5 and f 11, I prefer f 8. It is the the only super wide, on which I thought a little miracle might have happened to the 35 mm format optical industry, and which I judge as impressing as the MF 4.5/38 Biogon [ I feel the 4.5/38 as the best super wide I ever saw; additionally, both lenses (3.4/21 SA and 4.5/38 Biogon) perform very similar (sharpness, color rendition, out-of-focus rendition), at least when stopped down to f 8 ]. The 3.4/21 is pretty sharp, and comparable to the pre-asph (version 4) 2/35 Summicron or rigid chrome 2/50 Summicron. Both, the out-of-focus and the color rendition, also agree to the pre-asph 2/35: rich and with a lot of shades. In low light (i.e. f 4, 1/30 to 1/60, 200 ASA), it additionally accentuates white or bright areas, increasing the modeling effects. In my experience, the 4/21 M SA performs similar (although less sharp by far), but both, the 2.8/21 asph Elmarit and 4/21 R SA, perform remarkably different. Though more sharp, specially at lower f-stops, the 2.8/21 asph lens shows colors and contrasts, which agree to the color and contrast rendition/ management of the current 2/50 M Summicron or 1.4/35 ASPH Summilux, and which I feel as "too strong" or too much saturated (not always, but too often). Different, the 4/21 R SA shows a (slightly) reduced color scale, specially in bright sun shine. The shadow parts are very dark, almost black. And, although this special performence remembers on the Summar's color rendition, there is a difference in the viewers picture perception: The pictures, specially landscapes in bright sun light, get "restless", "turbulent", "unsteady", "nervous" (?, phrase). This effect results from the large number of changements of bright sun shine and (almost) black shadow, which cannot be avoided most of the times. The large number of changements results from the wide angle of the lens: you simply get "very much" in your picture. Additionally, there is another difficulty: Specially unexperienced 21 mm VF/RF users pretty soon get desperate, because the forground is "too empty". So, although I feel the 3.4/21 SA's rendition as more pleasant, I'd suggest the 4/21 R SA to beginners, because it is more easy to create the picture (you get what you see). The 3.4/21 is a neutral lens with a slight tendency to cold, the 4/21 R SA is a warm lens.
2/90 M Summicron:
The 2/90 M Summicron was introduced in 1957 (1980, 2nd version). I know the 1-st version pretty good, which is so fine, that Leitz needed 22 years to replace it by a (slightly) improved version (Erwin). And, to be honest, I hardly see any difference. It shows it's best performance between f 2.8 and 8, with an optimum at f 4, but you will get very fine results at f 8 also. To give an impression of the lens' rendition: Whenever I see a large (and good !) black & white picture or poster on a wall, kiosk, etc showing a person/-s, I have the feeling that this picture _must_ have been taken with the 2/90 M Summicron. The idea is my mind, before I realize that it's - of course - from an LF camera, and that it should have been less sharp. But, the example gives an idea, how rich the very special grey tone rendition of this lens is (Erwin notes, that she is famous for her "creamy" rendition). She is definietly less sharp than the 2.8/90 M Elmarit, and is the wrong lens if you want to document events. But, you will be in the b/w portrait heaven if you use her for exactly those pictures or "emotional" sceneries, landscapes included. It's a cold lens.
(permission to reproduce these comments was obtained from Mr. Breull)