50 Sonnar and the focus shift

[kinoglass]

I am sorry for the cconfusion I have created. I was referring to posting #42 suggesting a solution to corretc focursing. Indeed the sonnar C has not floating element. My comment was related to reflex systems, Hassselblad, Rolleiflex, etc., where the floating element iss used in certain Zeiss lenses. The ZM Sonnar Classic is designed to offer a modern lens, color correction, cotrast, aberrations, etc, with the image quality of the old classic.

 

[Huck Finn]

I am sorry for the cconfusion I have created. I was referring to posting #42 suggesting a solution to corretc focursing. Indeed the sonnar C has not floating element. My comment was related to reflex systems, Hassselblad, Rolleiflex, etc., where the floating element iss used in certain Zeiss lenses. The ZM Sonnar Classic is designed to offer a modern lens, color correction, cotrast, aberrations, etc, with the image quality of the old classic.

Kinoglass, I thought that your original post was clear that Zeiss has the technology to correct such problems - not that it had been implemented on the C-Sonnar lens in particular. 🙂

Huck

 

[kinoglass]

Well, as we know the greatly awaited 80mm Sonnar ZM has a floating element. And we also know that 50 C "problem" is not a problem but a virtue offered to the photographer to extend his ability to produce outstanding images. The fact that the focus shift moves in oposite directions with paterns along side the diagonal of the frame or square to it must give an enhanced sens of depth to the image.

 

[Huck Finn]

Well, as we know the greatly awaited 80mm Sonnar ZM has a floating element. And we also know that 50 C "problem" is not a problem but a virtue offered to the photographer to extend his ability to produce outstanding images. The fact that the focus shift moves in oposite directions with paterns along side the diagonal of the frame or square to it must give an enhanced sens of depth to the image.

There are also "work arounds" for any of these issues to exploit the characteristics of the lens. Focus shift on the C-Sonnar, for example is about half the depth of field & it is a front focus. Therefore, if after determining focus with the rangefinder, if the focus collar is re-set to the left DOF scale marker on the lens, the lens will then be set for the accurate point of focus. While this doesn't work for spontaneous shooting, it is perfectly doable for portraits, still lifes, etc. - many of the kinds of things that will be shot at or close to the minimum focus distance. For subjects that will be shot at a longer distance & when the precise point of focus is not so important, it is not so much of an issue.

 

[Huck Finn]

From Zeiss' TS -



:/

What does "TS" stand for? When was this correspondence dated?

 

[Huck Finn]

(T)ech (s)upport. 😀

I fired off an email to Zeiss sometime yesterday, and received a reply earlier this morning.

Strange. I received an e'mail from Zeiss in Germany 2 days ago saying the following:

Knowing the focus shift of the high speed Sonnar we had originally intended to adjust the rangefinder cam of the lens to a compromise: f/2.8. But this was probably not a good idea since many users seem to apply the lens very often wide open. In addition, the new Sonnar has much higher contrast wide open than the historical lens, which makes a focus error even more visible. So we have meanwhile decided to return the the cam adjustment at f/1.5. This is now applied in the production. But it implies that the focus shift at f/5.6 is even more significant.

Was your e-mail to Zeiss USA?

I had heard rumors a couple of months ago that they would be doing this, so I wasn't surprised when I received this report.

I wanted to know if the newer shipments of the Sonnar were calibrated for f/1.5 (to correct the shift); from the looks of it, it does not seem so. 🙁

It may be that they had not been doing this, but have just begun.

Do you (or anyone else for that matter) believe Zeiss created the Sonnar to shift at the 'lower' apertures?

No, I don't. But this is a design that was created more than 75 years ago before coatings. It was the first successful high speed lens that would be flare resistant. It was created to have a lens with improved speed over the Ernostar design for available light photography. Double Gauss designs were not viable until the creation of coatings that would reduce flare sufficiently for them to be usable. The fact that there is focus shift in this lens is something inherent in its asymmetrical design, not a feature that the designers were seeking to build into it.

 

[khagler]

people are holding back from buying this lens because of all this mess.

On the other hand, I didn't pay much attention to this lens at first (I already have a 50mm Summicron), but the large number of sample photos posted here supposedly illustrating the "front focus" problem have convinced me to buy one. ;-)

 

[galavanter]

Me too. I was going to get a 50 M-Hexanon (still might for $400.00) but the size and Tim's backyard tests have me seriously considering it. I am now telling myself I need one fast portrait lens, and a compact one at that.

On the other hand, I didn't pay much attention to this lens at first (I already have a 50mm Summicron), but the large number of sample photos posted here supposedly illustrating the "front focus" problem have convinced me to buy one. ;-)

 

[Noserider]

Ok, now I understand what Zeiss is doing for the fix. Readjustment of the initial group placement would do it, without altering the bokeh. Although, I still think altering the rear group a smidge would help. Like the DC Nikkors.

 

[FanMan]

I do not understand it! Is the focus shift after the re-adjustment now (a) not playing an important role anymore or (b) even more significant??? I think that would be good to know.

From Zeiss:


"Well, of course the focus shift still exists after re-adjusting the lens, but will not be visible at f/1.5. When you stop down to f/2.8 or smaller, there will be visible a slight focus shift, but sharpness will be covered within the depth-of-field. In practical use, after the adjustment the focus shift will not play an important role anymore."


They say it takes about 10 days for the adjustment.

from Zeiss in Germany 2 days ago saying the following:

Knowing the focus shift of the high speed Sonnar we had originally intended to adjust the rangefinder cam of the lens to a compromise: f/2.8. But this was probably not a good idea since many users seem to apply the lens very often wide open. In addition, the new Sonnar has much higher contrast wide open than the historical lens, which makes a focus error even more visible. So we have meanwhile decided to return the the cam adjustment at f/1.5. This is now applied in the production. But it implies that the focus shift at f/5.6 is even more significant.

 

[summilux]

let us build a serial number database to track the "shift" from 2.8 to 1.5, mine is 156004xx, it is not optimised for 1.5, my friend has one 156007xx, which has seen much use.


I like the bokeh of this lens very much, and according to my personal experience, at wide open, discounting the focus shift, it is very sharp.

 

[Huck Finn]

let us build a serial number database to track the "shift" from 2.8 to 1.5, mine is 156004xx, it is not optimised for 1.5, my friend has one 156007xx, which has seen much use.

From Zeiss:

"Unfortunately the order of the serial numbers is not completely straight, so we can't tell from the serial numbers how the lens is adjusted."

 

[visiondr]

let us build a serial number database to track the "shift" from 2.8 to 1.5, mine is 156004xx, it is not optimised for 1.5, my friend has one 156007xx, which has seen much use.


I like the bokeh of this lens very much, and according to my personal experience, at wide open, discounting the focus shift, it is very sharp.

Holy Bokeh Batman!
That is beautiful.
Maybe this Sonnar can be my fast 50. However, I may have to have the focus shift adjustment.

 

[Krosya]

I do not understand it! Is the focus shift after the re-adjustment now (a) not playing an important role anymore or (b) even more significant??? I think that would be good to know.

Thats what I would like to know too - once adjusted to focus correctlt at 1.5 - is it worse at other settings? Did anyone have thier Sonnar re-adjusted to focus correctly at 1.5? If so - pls post results here.
I really want to like this lens as some of the results from it that I have seen are great, yet......this whole focus shift issue is stopping me.

 

[tbarker13]

If no one gets to it sooner I'll post photos from my adjusted sonnar once it returns home.

 

[back alley]

...once adjusted to fucus correctlt at 1.5 - is it worse at other settings?...

yes, the focus shift just moves to the smaller apertures but the greater dof should cover that.

 

[kinoglass]

The focus shift happens as the lens is stoping down and it is noticeable at close distances. Now, ZEISS decided originally to couple the lens focusing to the camera RF when the lens was stopped down at f2.8. That meant that between f2.8 and f5.6 the focus shift (always positive) would have been less noticeable than between f1.5 and f5.6 . . .now ZEISS is saying that because so many people are using the lens at full aperture f1.5 it will calibrate the lenses in proiduction at f1.5 meaning; when you focus and shoot at f1.5 no focus error will take place between the lens and the RF. ZEISS also says how to correct the focusing using the DOF scale and the lens index when closing down the lens. So, no problem.

The beauty of the SONNAR is that all this is happening in the center of the image, where things are this predictable, but on the perimeter the out of focus effect occurs in two directions, towards the front and towards the camera, depending of the patern of the image direction, what they call sagittal and tangential, this is WHAT MAKES THE SONNAR SO ESPECIAL and leads to its three dimentional BOUQUET.

The LAST thing we want to do is to give ZEISS the impression that photographers are disapointed with the lens focus shifting and that what we want is a flat field Plannar. We like the SONNAR and love its CLASSICAL image rendition! We want ot keep it so. And I am getting one.

The SONNAR was patented in 1931 for the f2 version and a year later for the f1.5 by Bertele. A job well done.

 

[foto_fool]

Me too. I was going to get a 50 M-Hexanon (still might for $400.00) but the size and Tim's backyard tests have me seriously considering it. I am now telling myself I need one fast portrait lens, and a compact one at that.

I have the M-Hexanon and love it, but went for the Sonnar for the "LOOK" - and my first roll back from the processor has made a believer of me.

And believe it - this lens is very small for a fast 50 - almost 1/4 inch shorter than the 1-stop-slower Hexanon.

NOTE TO ZEISS - Thanks for making this great lens!

- John

 

[FanMan]

Thats what I would like to know too - once adjusted to fucus correctlt at 1.5 - is it worse at other settings? Did anyone have thier Sonnar re-adjusted to focus correctly at 1.5? If so - pls post results here.
I really want to like this lens as some of the results from it that I have seen are great, yet......this whole focus shift issue is stopping me.

I want to be absolutely sure about the consequences of a re-adjustment. Before sending my c-sonnar to Zeiss I will wait definitely wait for results posted here. At the moment the statements of Zeiss seem to be contradictory (which applies btw also to the Zeiss statement that ZM lenses are especially corrected for focus shift).

 

[kinoglass]

If the lens and the camera RF agree at f1.5 the shift will be noticeable at f2.8 and f5.6 compared to f1.5. If the lens and the RF are adjusted for sharp focus at f2.8 there will a noticeable shift at f1.5 and f5.6.

The lens focus shift is NOT ADJUSTED as it is part of the lens behavour by design. The issue is at what APERTURE will the Range Finder and the lens match. Keep in mind either way corrections can be applied by the photgrapher to bring the lens back to sharp focus.