Huck,
The C Sonnar is tricky to use at short distances (< 6 ft).
I am 90% certain example does front-focus wide open at the minimum focus distance. It turns out I did tests using a 3D subject at the minimum focus distances of several of my lenses (RF, Nikkor AI/AIS and Mamiya/Sekor M42) during Christmas break. I would be happy to email you C Sonnar examples at the minimum focus distance for f 1.5, 2.0, 2.8 and 4.0. I'm not going to post them because at the time I didn't know this would become a hot topic, and while I focused carefully, the DOF for f 1.5 at the minimum focus distance of 0.9 M is only 0.027 M or 1 inch. With my subject a very small focus error could appear to large effect. Frankly I'm not sure I can focus that carefully. Also, somebody will jump in and say these photos are not a proper test, etc, etc.
I have three things to say about the C Sonnar.
1. My test is entirely consistent with the information from Zeiss posted about the C Sonnar focus shift posted in the LL update. At 2.8 the shift looks like it's gone and at f 4 the subject I chose is well rendered (sharp).
2. My serial number is 1560085X.
3. At the risk of being viewed as a Zeiss "fan boy" I really don't understand what the fuss is about. Is any fast 50mm lens versatile wide open at distances of less than 6'? For f 1.5 at less than 6' if the camera moves by a half inch between the time you focus and the time you push the shutter release, what you know you focused on is no longer the point of focus and much of your DOF moves.
Distance(ft)___DOF at f 1.5
4______________2"
6______________4.6"
10_____________1.1'
Using a Canon 50/1.2 LTM taught me that very fast lens are of limited practical use at relatively close distances. Now, consider that one useful way to focus (an any f stop) is to intentionally back focus a bit to make the most use of the DOF you have. Of course for fast apertures at close distances how much back focus to use is a guess. You can use the C Sonnar like any other fast 50mm lens, i.e. intentionally back focus. But a hand-held rangefinder with a wide open fast lens is not the way to make a carefully focused photo at close distance. You need a tripod or better yet, a fast lens on an SLR (and a tripod). My Nikkor 35/2 CRC with floating elements excels at non-macro close ups and it is really sharp too.
I accept that fact that the C Sonnar is not the lens to use if you want to take close ups at f 1.5. I would not hesitate to use it near the minimum focus distance at f 2.8. I have used it at distances of about 6 ft wide open and obtained useful images (one of these I posted here recently). It makes lovely photos wide open (in my opinion) at reasonable subject-to-lens distances. Joe posted several examples.
Fast 50mm lens are great. But all of them are a challenge to use wide open at distances of less than 10 ft. Like any lens, the C Sonnar has strengths and weaknesses, so in the end one compromises. Even a brand new 50mm Summilux is a compromise because the cost benefit ratio not favorable (but is is acceptable for many).
I plan to just go out and take photographs with my C Sonnar. What I've learned from this controversy will increase my chances of getting useful photos at distances of less than 10 ft. But I'm done reading or talking about this lens.
Huck, I hope this is of some use to you.
willie
