Collapsible Summicron’s Performance at f/2?

I have used the 50mm Summicron f2.0 collapsible lens as my main lens since 1967. The lens itself dates back to 1954. Like all Summicron it is very sharp, even at f2. It is unlike a modern lens of same name, in being lower contrast. Lower like almost minimal! I previously lived in Southern Africa, where the lower contrast was very welcome. You can always push up contrast..by longer developing of B/W or in Photoshop with scanned images.
The look of the softness at maximum aperture is very welcome in portraits of women! No soft focus filter required. This comment made me do an apology to another member, as my comment came to a photo posted while I made it! It was his wife and daughters. I used my lens at "Pride 2011 Toronto". All were shot at f2.0.I shot close ups of some of the participants. A few missed spot on focus(me) and a few to flare casualties.
The lens exhibits "doughnut shapes" in out of focus areas, at maximum aperture. It has always done it, as all its same series do! It is normal for the collapsible. Are there any special problems? Yes! One my lens is pristine, both front and back elements are not marked by cleaning. The front protected by a Leica UV or IA filter. Two. Flare! The lens gathers it's own internal haze so pix made with strong sources of light can kill your shot! A lens hood an absolute requirement. There will still be losses. The filter adds to the flare losses.
Finding a "clean" lens very difficult. It is worth it. It was good enough for Cartier-Bresson. He also used a Zeiss Sonnar 50mm collapsible! In some photos if you look carefully it is not always the Summicron! The Zeiss lens is sharper, higher contrast.
Sometimes I wish it had less flare. I have never added to my 50mm. I use other camera systems so easy today with falling prices. Some systems were gifts. The Super Takumars of Pentax have zero flare. The Nikkors are all sharper. The Micro-Nikkor my sharpest, contrastiest lens, even at infinity!
No other 50mm lens I use has this wonderful look. I actually hate the look of the aspherics of Leica. The backgrounds look like broken shards of glass. They are all obviously sharper and more contrasty.
The big plus is the collapsible feature. Easy fits under jackets, coats and outer clothing.A Leica with collapsed lens, no meter in shoe looks harmless. Get access to all sorts of events as it's not a real camera. A friend of mine tried that at a Jazz concert in Cape Town some years ago. He has similar rig. "NO way!" said security."you have the most professional camera!" That is a very rare instance.
I find the Elmar have higher contrast and a " solid block" look. Earlier Summilux appear to give a lighter more delicate image. All these are really subtle. In an age of overgrown monster size zooms, it's wonderful Leica has all these small lenses. Smaller than lenses supplied with smaller format digital cameras.

he said it well. However having owned and used one for many years I'd add that all up it's probably better than it's being described. It was the absolute top lens of its time and the working tool of MANY famous photographers. No,it's not at its best wide open, few lenes were, but as mentioned a bit of contrast and you'll have trouble picking out the print from more contemporary lenses. It's a fine lens as is its predecessor the Summitar.

I used a collapsing Summicron for years, often wide open, and loved it. There's no point in posting an example here: small digital images don't do this lens justice. Do be careful in cleaning these lenses. I finally retired mine due to cleaning marks. It was wonderful for photos of people with more wrinkles than they wanted to show, though.

A clean collapsible Summicron is not easy to find; but paired with a SOOFM hood, it can tackle just about anything. I'd not call it the best of its time, specially because of the contenders from Zeiss: but certainly it was an advance over the Summitar. Its wide open performance can be likened to that of earlier fast Leitz lenses: Summitar, Summar, Xenon, Hektor.

The cleaning marks issue is major with soft-coated Leica lenses like the collapsible Summicron. The coating is very soft, ANY pressure applied during cleaning will mark it or remove it. Under that, the glass of the front lens element is also very soft, it is "flint" (lead crystal) glass. Also, the whale-oil lubricants will fail over time, and they will leave haze inside the lens, which must then be chemically cleaned by an expert. Finally, the earliest ones had some elements with thorium-containing glass, which is naturally radioactive, and turns brown due to the radioactivity. (That can be bleached temporarily with strong UV light.)
So condition is EVERYTHING on the collapsible Summicron.
If you want something that's closer to a "sure bet", and is a very fine lens, consider the LTM Canon 50/1.8. The all-chrome ones only rarely have haze problems, the black and aluminum ones are more prone to internal haze, which may be fater. They are hard-coated, so they are rarely scratched-up.

I had one (coupled to a fine 1950s double stroke M3) for too short a time in the mid 1980s to critically notice how it compared to others at that time (in particular, a more recent 1980s Sumnmicron). I guess I considered the softer contrast as having more to do with my darkroom development variations than anything else and which I compensated for in enlarger printing. I think that this early 50's lens (apparently designed in 1949), the successor to the Summitar, is described in Erwin Puts compendium (and which seems to agree with the above comments), where he says:

"At full aperture overall contrast is low to medium, and coarse detail is rendered with good clarity over most of the image field, corners excepted. The fingerprint of this lens is almost identical to that of the Summitar. Very critical inspection will reveal some finer differences. The Summitar has slightly better center performance, whereas the Summicron has a more even performance over the whole image area. One might assume that the designers paid more attention to an even coverage as this lens was supposed to be the prime lens for the Leica system."

It seems that one of the problems of that period was the availability of top glass compositions and a number of these lenses could be sharper and with better control of aberrations with modern glasses, irrespective of the advantage of more modern computer design of optics. Puts suggests that the suffix "cron" may well have been prompted by Leitz's ability in the early 50s to obtain a rare earth composed crown glass (Kron-glass) from a British supplier.

What usually overwhelms me more are the communicative/compositional qualities of good images than their absolute technical perfection and I even enjoy the effect of an admittedly flare-prone early 1930s Elmar in some images. I guess I wouldn't worry too much about any softness of contrast or off centre detail in the collapsible Summicron, unless I was doing landscape or architectural photography, in which case I probably would choose not to use my 35mm film camera.

Why not just buy a 1.5/50 Voigtlander? All 2/50coll are overpriced now (eBay: 700USD) with any amount of cleaning marks and haze thrown in for free. The CV1.5/50 costs new 700 USD. A used/pristine one on eBay goes for 350. Or are we talking antique jewelry here? The 2/50coll today is a special purpose lens, nicely reflected by the fact that a lot of owners also carry a more modern 50mm lens 'for general shooting'. Twice the price, twice the weight/bulk, more lens changes/time, lost shots...
Softening can be done much easier than sharpening (both in PS and wet processes). Besides, lots of H.C-B.'s pictures turned out truly soft whenever printed on 20x24 (plus margin), not only "low contrast".
I still shoot with a 2/50v4 I bought used ten years ago, for 400 USD. First M 50mm I bought. Unless I get a 1.4/50A for free, this Summicron is going to stay with me 'forever'. 'Upgrading lenses' makes no sense, economically. Knowledge (know the matter and yourself) and patience always get you the good deals in the long run.
If I ever needed softened portrait prints I'd produce them off of a sharp negative I could fearlessly blow up anytime in the future. Two lenses in one, kind of. That's what I pay for in a Leica lens.

In total, I think everyone has answered my initial question quite well. Thank you.

I am not looking for ‘antique jewelry’. I am looking for a faster lens, that gives good results, and is period-correct. It would help if it didn’t make my kit look like a jeepney. ;-)

The Zeiss Sonnar 50mm collapsible appears to be frequently faked and few were made for LTM. I probably wouldn't be able to tell the difference of fake vs. real over the web.

I'm also interested in the LTM Canon 50/1.8. These aren't cheap either but I have seen the results of these and have been very impressed.

"The 2/50coll today is a special purpose lens...", what is that purpose?

Thank you,
Jim

I love my Col. Summicron at all apertures, but to save money you should consider the LTM 50mm f:2.0 Nikkor. They came with "Tower" cameras from Sears, and are slightly improved, coated copies of the Zeiss Sonnar.