50 Sonnar and the focus shift

[willie_901]

My feelings are similar to Noserider's.

Focusing a 50mm lens with a hand-held RF close up (inside of 8-10 ft.) at f-stops wider than 2.8 is pretty much hit or miss anyway. Movement (subject and/or photographer) between the time focus is set and the shutter is triggered has a profound effect because the DOF is so thin.

willie

 

[back alley]

i'm keeping mine as is also.
i will use it wide open but i am not usually at the minimum distance anyway.

joe

 

[Huck Finn]

I can see the front focus, too.

It would be great if you could share your experiences with us by posting some sample shots taken after the re-adjustment of the lens by Zeiss.

How much are the cost of the re-adjustment?

Michael

Michael there is no cost for the re-adjustment & no cost for return shipping. The customer pays only for the cost of the initial shipping to Zeiss in Germany.

 

[Huck Finn]

I too also wonder what the rationale was by the Zeiss engineers and designers to produce a fast expensive 50mm lens that front focuses at f1.5? ... as if the f 1.5 opening is not going to be used.
since the problem can be semi corrected or a lesser of an evil trade off can made,are the new current C f 1.5 Sonnars coming off the assembly line corrected or adjusted for this serious problem?

people are holding back from buying this lens because of all this mess.
I expect better from Zeiss.

Yes, xayraa33, the new current ZM 50/1.5 C-Sonnars coming off the assembly line have the cams adjusted for best focus at f/1.5 instead of f/2.8.

Whatever the rationale, for the original decision, I think that if you asked the decision makers at Zeiss today, they'd probably say it was a bad idea. I know that they felt that f/2.8 was the best compromise setting for a focus shift that affects apertures from f/1.5 to f/5.6 & enabled best performance at almost all apertures. I think that they believed that the user could learn to compromise for the shift at f/1.5 or use it for pictures in which the exact point of focus wasn't so important, which is probably why they advertised it as the "photojournalist's lens - as someone else on this forum suggested - intended for shots that were not close up & therefore not at the shallowest DOF. Again, my hunch is that they probably regret that decision. Even smart people selling expensive items sometimes make misguided decisions. I'm sure that Leica regrets the decision to come out with the M8 only to have to recall it to fix a problem that shouldn't have been there in the first place. These things happen.

Anyone who gets the lens maximized for f/1.5 should realize that the focus shift will then be transferred to smaller apertures as the apeture is stepped down. Although Zeiss appears to be saying that the shift will be covered by DOF, the intended point of focus will still not be at the optimum point of best focus & may appear softer than the same picture would with the lens optimized for f/2.8.

 

[back alley]

i wonder how one could tell when the shift was made, that is which serial numbers would indicate the changed lenses?

 

[Huck Finn]

I had the same question. When I contacted Zeiss, I was told that "unfortunately the order of serial numbers is not completely straight - so we can't tell from the serial numbers." Sooo . . . I guess you just shoot with it or run your own tests & if you don't like the results, send it back.

I had heard this rumor a couple of months back but have only been able to verify it recently, so my guess is that the change was made sometime in 2007 - late winter or early spring is my best guess. (Of course, it could have been earlier. I'm just guessing.) If someone who is buying new can verify from their dealer that it the dealer received it this spring, then chances are it's set for f/1.5.

 

[Noserider]

Oh here we go. If the bokeh of the lens is affected (which I'm sure it is, since the adjustment would be in the spacing of one of the elements) then I'd rather have a 2.8 optimized lens. Look for the value of 2.8 optimized lenses to go thru the roof. Or in another way, Zeiss just made an instant rare cult lens. Crap, I knew I should have bought the low serial number loaner from Zeiss.

 

[sebastel]

Oh here we go. If the bokeh of the lens is affected (which I'm sure it is, since the adjustment would be in the spacing of one of the elements) then I'd rather have a 2.8 optimized lens. Look for the value of 2.8 optimized lenses to go thru the roof. Or in another way, Zeiss just made an instant rare cult lens. Crap, I knew I should have bought the low serial number loaner from Zeiss.

bokeh NOT affected.
no changes in the spacing between single groups, but only in the spacing of the complete lens (relative to sensor/film surface).

 

[tbarker13]

I was told by Zeiss that the adjustment would have no impact on the character of the images created.
I just bought my lens about 3 weeks ago. I must have gotten one that was still in stock from the older 2.8-optimized versions.
Oh well, it should be arriving in Germany on Monday for its "fix."

 

[Noserider]

Um, I don't see how changing the 'spacing of the complete lens' would have any effect other than *focussing* the lens. Must be changing just the front group or rear group spacing. Which would cause change to spherical abb. and thus, optical character/bokeh. Must.

 

[sebastel]

oh dear ...
did you ever watch how a lens gets focused? the whole lens is moved relative to the film/sensor plane. and it is exactly this adjustment that gets correction.

things are so simple you cannot see them.

 

[rogue_designer]

Um, I don't see how changing the 'spacing of the complete lens' would have any effect other than *focussing* the lens. Must be changing just the front group or rear group spacing. Which would cause change to spherical abb. and thus, optical character/bokeh. Must.

In effect, the adjustment is pairing the lens to focus properly at 1.5, the same as shimming the lens to film distance to accomplish this. There is no other adjustment being made.

 

[xayraa33]

this is very good news from Zeiss.
an f 1.5 lens that can be used at f 1.5.

 

[kinoglass]

Me thinks no shimming and no spacing alterations. The key is the cam angle coupling to the Rf wheel. Changing or machining the cam is all what is required to make the focusing point of the lens at f1.5 coincide with the RF . . .The focus shift as a function of aperture setting will remain and according to Zeiss it is pretty predictable. The center image is mostly affected and little in the periphery is noticeable making the lens a great performer dealing with spatial non flat subjects. A very refine tool indeed.

 

[Rico]

I have an intriguing idea (patent pending 🙂). Correct RF feedback for distance and aperture is achievable for those optical designs that exhibit focus shift. While distance is linked to the RF cam in the normal fashion, the aperture setting in my design will also influence the cam. Mathematically speaking, it is a function of R²->R. The trick is a mechanical solution that can fit within the confines of a standard RF lens.

 

[kinoglass]

Well, ZEISS has already solved the problem. Very good spatial definition plus a FLOATING element to correct the focus shift. The results are sensational (and expensive) The problem is only one with no reflex systems like the ZM since with a reflex system the photographer focuses the lens to sharpness, he might not refocus closing down the lens, but how many CLASSIC Sonnars are there on reflex systems?

 

[xayraa33]

It would be nice if there was a way to ID the newer corrected ZM Sonnars.
I do not think that Zeiss would engrave a "Mk. II" or maybe a " * " on the front name ring.

 

[Krosya]

Well, ZEISS has already solved the problem. Very good spatial definition plus a FLOATING element to correct the focus shift. The results are sensational (and expensive) The problem is only one with no reflex systems like the ZM since with a reflex system the photographer focuses the lens to sharpness, he might not refocus closing down the lens, but how many CLASSIC Sonnars are there on reflex systems?

Do I understand you correctly - all currently sold ZM Sonnars are corrected and don't have this focus shift problem? If this is indeed the case - where did you get this info? Is there official statement from Zeiss?
Or did I misunderstand you completely and all current ZM Sonnars are same as before, - have focus shift issue?
Could you clarify pls.

 

[john_s]

Well, ZEISS has already solved the problem. Very good spatial definition plus a FLOATING element to correct the focus shift. The results are sensational (and expensive) ..........

Also, floating elements add complexity to the mount, making it bigger and heavier. One of the things I like about the C-Sonnar is its compact dimensions. A rangefinder camera feels different with a bigger lens. I still like my little pre-ASPH 35mm Summicron even though I have a better 35mm lens that happens to be significantly bigger.

 

[Mazurka]

Well, ZEISS has already solved the problem. Very good spatial definition plus a FLOATING element to correct the focus shift. The results are sensational (and expensive)

The C-Sonnar does not have any floating elements.