Sonnar C 1.5/50 focus shift - Leica M6 vs ZI

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Peter_S

Peter_S
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Hi!

I was wondering - does anybody have practical experience with the focus shift of the Sonnar C on the Leica M6 and the Zeiss Ikon ZM?
I am not sure why it should differ, but here and there one reads it differs. I have an M6, had an M8 and briefly had a ZI before. The shift was certainly more of an issue on the M8 (which I somewhat understand), but I had the ZI too briefly to tell.

My M6 is down and I am pondering whether to get another M6 or an Ikon while my prime M6 goes off for repair.

Thanks,
Peter
 
Since focus shift is a function of the combination of lens + image recording surface there should be no difference between Leica M6 and ZI if the film has same degree of flatness in both cameras.
 
What Gabor said. I've shot my C-Sonnar on an M4-2, M4-P, M8, and M9. The focus shift occurs on each camera the same way, as far as I can tell, close to or at minimum focus distance.
 
Focus shift shoukd be the same as stated above. However, I have heard several claims that ZM lenses in general focus better on the ZI. I have not bothered so far to test these claims.
 
Chriscrawfordphoto said:
My ZM lenses focus flawlessly and VERY sharp on my two M6 bodies.
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I have no problems with my ZM on the M6 either. I read somewhere that the RF on M and ZI are calibrated for different distances. If this has any practical repercussions, I have no idea. I have also noticed that when no lens is attached, the RF patch position on my M6 is exactly at 2 meters, while on both my ZI, it is at 70 cm.
 
To be a bit more precise, the impact of focus shift is dependent on how the c-sonnar is optimized, subject distance, and f-stop. For example, if the lens is optimized at f2.8, focus shift will be most evident at MFD at f1.5. If the lens is optimized at f1.5, focus shift will be most evident at MFD around f2.8. In both cases, as you stop down and subject distance increases, the impact of focus shift will lessen.

Practically, imho, you may want a lens optimized at f1.5 if you shoot more wide open and close in. You may want a lens optimized at f2.8 if you shoot more at f2.8 and narrower apertures and not frequently close to MFD.

Hope this makes sense. In practice, honestly, I just shoot and don't notice the shift. If I'm really close, I'll "bow" a little toward the subject at f1.5-2.0 (mine is f2.8 optimized) if I remember. Doesn't seem to matter that much in use, really.
 
MCTuomey said:
To be a bit more precise, the impact of focus shift is dependent on how the c-sonnar is optimized, subject distance, and f-stop. For example, if the lens is optimized at f2.8, focus shift will be most evident at MFD at f1.5. If the lens is optimized at f1.5, focus shift will be most evident at MFD around f2.8. In both cases, as you stop down and subject distance increases, the impact of focus shift will lessen.

Practically, imho, you may want a lens optimized at f1.5 if you shoot more wide open and close in. You may want a lens optimized at f2.8 if you shoot more at f2.8 and narrower apertures and not frequently close to MFD.

Hope this makes sense. In practice, honestly, I just shoot and don't notice the shift. If I'm really close, I'll "bow" a little toward the subject at f1.5-2.0 (mine is f2.8 optimized) if I remember. Doesn't seem to matter that much in use, really.
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I have set my sights on the C-Sonnar as a fast 50 for some time already. Love the way it renders wide open and stopped down.

But the internet buzz about its focus shift issues always make me think twice about it. Nonetheless I had also read about people "compensating" for the focus shift by 1) not aligning the images in the focus patch 2) what you described.

Another question: is it "optimised" at f1.5 from factory?
 
Vincent.G said:
Another question: is it "optimised" at f1.5 from factory?
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I can't answer, Vincent. What I can say is that I bought mine new over 2 years ago from popflash and it is optimized at f2.8.

By the way, "optimized" signifies that the normal distribution of depth-of-field takes place at the optimized aperture setting. Thus, there should be less focus error at the optimized aperture than at other selected apertures between f1.5 and f2.8-4. At narrower apertures beyond f2.8-4, there is much less potential for focus error due to the greater depth-of-field, and so the optimization choice doesn't practically matter.
 
Vincent.G said:
I have set my sights on the C-Sonnar as a fast 50 for some time already. Love the way it renders wide open and stopped down.

But the internet buzz about its focus shift issues always make me think twice about it. Nonetheless I had also read about people "compensating" for the focus shift by 1) not aligning the images in the focus patch 2) what you described.

Another question: is it "optimised" at f1.5 from factory?
Click to expand...

The Zeiss sales mgr for USA told me that all of the 50 mm f1/5 Sonnar ZMs made since 2007 have been optimized for f1.5 at the factory. I've read that elsewhere too. OTOH, when I e-mailed Zeiss in the old country they told me that the lenses were optimized at f2.8. The USA rep sort of snorted when I told him that and said he'd need to take it up with the factory contact with whom I corresponded. I tend to think that the USA rep had it right. He's on the front line, and this is a question that gets raised a lot on variouis fora over here, so his dealers must have passed the question on to him too.

My real world experience is consistent with whoever posted that this doesn't play a big role in everyday photography. YMMV.
 
ChipMcD said:
The Zeiss sales mgr for USA told me that all of the 50 mm f1/5 Sonnar ZMs made since 2007 have been optimized for f1.5 at the factory.
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For what it's worth mine was purchased new from B&H in 2010 and is optimized at 2.8.

When shooting wide open and at close range I find the 'lean in' method the most accurate, but some like to compensate in the viewfinder. There is so much chatter about this issue on the internet that I nearly talked myself out of this lens (like Vincent is doing). I'm glad I didn't because the lens is just great.
 
I bought mine one year ago from Zeiss directly (after testing it) and it is definitely optimized for f/2.8. Also Zeiss Germany confirmed this.

I love the lens, I shot it 90% of the time, and would not trade if for anything (I sold my M8 and Biogon 2/35, it just did not compare to M6+Sonnar. Not because of film vs digital, but because of the lens).
I learned how to compensate, too, my initial questions was more curiousity than a real necessity. I keep shooting M6 + Sonnar C then.

Peter
 
Mike, ChipMcD and jawarden, many thanks for your input!

Looks like testing must be done to confirm the aperture it is "optimised" from factory. ;)
 
I'm interested in this lens too (for a Hexar RF body). Your cool explanations here did put away my fears on focus shift for daily use. But, not only for this lens, if I really would like to know the focus shift of my lens at wide apertures: Is there a simple test procedure (having no test equipment at all) to draw a dedicated FS curve for a specific lens using a film roll for this purpose?
 
dct said:
I'm interested in this lens too (for a Hexar RF body). Your cool explanations here did put away my fears on focus shift for daily use. But, not only for this lens, if I really would like to know the focus shift of my lens at wide apertures: Is there a simple test procedure (having no test equipment at all) to draw a dedicated FS curve for a specific lens using a film roll for this purpose?
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Well testing lenses is a rather boring and unrewarding activity, but if you feel it helps you to get to know your lenses better in the beginning, the easiest would be to take a series of closeup pictures of a diagonal ruler or something at minimum distance. Keep the camera on a tripod so that you don't move it between shots, vary the aperture and shutter speed and shoot the scene at various apertures. Write the aperture on a piece of paper that you keep in the picture for each shot. Keep focus at the same mark for all the pictures and see where focus falls at various apertures in the final picture.

You won't need a whole roll for that. Use the remaining pictures for taking a lot of nude closeup portraits of a beautiful woman (at various apertures if you want) and see what the Sonnar is really meant for.
 
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