3 ZM lenses reviewed

Mine is 156008xx... I'm not generally one to make newspaper, ruler, or brick wall tests, nor do I often find myself using a fast lens wide open. But I did make some shots faster than f/2, wide open or very nearly so, with the C-Sonnar at a photo club meeting in October. While certainly not definitive data, I didn't notice anything unusual about the plane of focus. Focused on the front pear, and in the other on the Hasselblad.

Edit: Using Z-I body.
 

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For those considering a high speed 50 without rf coupling issues, tack sharp central zone of focus, flare free shots, excellent bokeh and minimum focus of 0.7 m at a price close to the Sonnar-C, I think a used late pre-aspheric Summilux might do better. The Nokton might do better on paper but I don't think it can touch the bokeh or build quality of the late pre-asph. Summilux.
 
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I might deserve a spanking for asking such a basic question, but, what does the aperature have to do with the actual plane of focus of a given lens? In other words, the focal plane distance is exclusively deterimined by the relationship of the lens elements to the film plane, and linked to the rangefinder mechanism via the cam and so on. The lens iris blade opening determines the aperature setting which effects the amount of light entering the lens and creates the apparent depth of field zone. At large and small aperature settings, certain anomolies can occur, such as diffraction, flare and vignetting. The actual focal plane remains constant at any given aperature setting because the lens elements are not moved by the adjustment of the aperature. I would propose that the lenses commented on above are in fact mis-adjusted at the factory, and they appear better focused at middle aperatures because the intended focal plane then falls into a widened focal zone. (whew!) Please correct me if I am not informed properly on this point.

I have not performed any scientific tests of my Sonnar C 50/1.5, but after reading this thread, I intend to. So far, my casual touristy snaps and informal interior portraits on a ZI body have been extremely satisfying. I've had no obvious focal plane problems. Nice and sharp where I want it. And, over-all, I love the signature of this lens, what ever that means. lens sr #156001xx
 
It does indeed sound like what you describe, Nebula: mis-adjustment in the factory, the focal wall (thickness determined by the DOF) does not overlap with the RF target. Check out http://www.rangefinderforum.com/forums/showthread.php?t=34185, if you do test shots as shown in the lower half of this thread you will know immediately. And I suggest you use a tripod and also compare real distance to lens distance markings. And, BTW, this type of QA issue can also happen with other lenses. I've seen it on a 50/1.5 Nokton,
and a 135 Tele Elmar.

Joe, I am very much looking forward to your pictures. Maybe some one-side lighted portraits in the near future with that lens ?

Thanks,

Roland.
 
awilder said:
For those considering a high speed 50 without rf coupling issues, tack sharp central zone of focus, flare free shots, excellent bokeh and minimum focus of 0.7 m at a price close to the Sonnar-C, I think a used late pre-aspheric Summilux might do better. The Nokton might do better on paper but I don't think it can touch the bokeh or build quality of the late pre-asph. Summilux.
Click to expand...


"The Nokton might do better on paper but I dont think it can touch the bokeh or build quality of the later pre-ASPH Summi."

🙁

Many regard the nokton as very well built and extremely solid. Bokeh is subjective as heck and a personal thing....this seems to be one of the more biased and groundless comments in this thread.
 
Nebulon said:
I might deserve a spanking for asking such a basic question, but, what does the aperature have to do with the actual plane of focus of a given lens? In other words, the focal plane distance is exclusively deterimined by the relationship of the lens elements to the film plane, and linked to the rangefinder mechanism via the cam and so on. The lens iris blade opening determines the aperature setting which effects the amount of light entering the lens and creates the apparent depth of field zone. At large and small aperature settings, certain anomolies can occur, such as diffraction, flare and vignetting. The actual focal plane remains constant at any given aperature setting because the lens elements are not moved by the adjustment of the aperature. I would propose that the lenses commented on above are in fact mis-adjusted at the factory, and they appear better focused at middle aperatures because the intended focal plane then falls into a widened focal zone. (whew!) Please correct me if I am not informed properly on this point.
Click to expand...

That was what I thought until recently. The 45/2.8 Tessar of the Contax SLR C/Y mount was also famous for this focus shift due to aperture setting problem. I owned this lens and also have so for no problem with it. The advice from the Contax people are when using this lens either u take at f2.8 (no focus shift problem) or beyond f8 (where the DOF will take care of the focus shift problem).

Just to share.
 
Nebulon said:
I might deserve a spanking for asking such a basic question, but, what does the aperature have to do with the actual plane of focus of a given lens? In other words, the focal plane distance is exclusively deterimined by the relationship of the lens elements to the film plane, and linked to the rangefinder mechanism via the cam and so on. The lens iris blade opening determines the aperature setting which effects the amount of light entering the lens and creates the apparent depth of field zone. At large and small aperature settings, certain anomolies can occur, such as diffraction, flare and vignetting. The actual focal plane remains constant at any given aperature setting because the lens elements are not moved by the adjustment of the aperature. I would propose that the lenses commented on above are in fact mis-adjusted at the factory, and they appear better focused at middle aperatures because the intended focal plane then falls into a widened focal zone. (whew!) Please correct me if I am not informed properly on this point.

I have not performed any scientific tests of my Sonnar C 50/1.5, but after reading this thread, I intend to. So far, my casual touristy snaps and informal interior portraits on a ZI body have been extremely satisfying. I've had no obvious focal plane problems. Nice and sharp where I want it. And, over-all, I love the signature of this lens, what ever that means. lens sr #156001xx
Click to expand...

The focal plane has to do with the point at which the light rays converge for the best point of focus. This plane shifts as the aperture is widened or narrowed & are rays are included or eliminated. It is why some lenses are made with floating elements so that the lens adjusts for this shift mechanically, thereby keeping the image in focus. See the link below for a better explanation than I could ever hope to offer:

www.vanwalree.com/optics/spherical.html

What I don't understand in some of the earlier posts is the idea that Zeiss may have optimized the C-Sonnar for different apertures. Normally a lens without floating is optimized for the maximum aperture so that any less-than-optimum plane of focus problems occur at smaller apertures where depth of field should cover any focus errors. At least, that is my understanding.
 
fuwen said:
... The 45/2.8 Tessar of the Contax SLR C/Y mount was also famous for this focus shift due to aperture setting problem. I owned this lens and also have so for no problem with it. The advice from the Contax people are when using this lens either u take at f2.8 (no focus shift problem) or beyond f8 (where the DOF will take care of the focus shift problem).
Click to expand...
You can focus at the taking aperture with an SLR, but using a lens with focus shift on an RF sounds like a real pain. You can have some fun with lenses that lack field flatness, but this focus-shift aberration is just bad optical design.
 
sebastel said:
i own one c-sonnar, and i also had some communication with zeiss technicians about it.
they told, that it is adjusted to focus correctly at f/2.8, and because of the focus shift it will front focus at wider apertures. they will adjust it to your needs, if you want it.
Click to expand...

This makes no sense to me. Why would an f/1.5 lens be adjusted to focus correctly at f/2.8? You buy the lens for its capabilities at f/1.5. If you cared more about its performance at f/2.8, you could save a lot of money & buy a cheaper lens. Not to mention the slim depth of field at f/1.5 which makes accurate focus at this aperture critical.
 
sebastel said:
i own one c-sonnar, and i also had some communication with zeiss technicians about it.
they told, that it is adjusted to focus correctly at f/2.8, and because of the focus shift it will front focus at wider apertures. they will adjust it to your needs, if you want it.
Click to expand...
If Zeiss technicians really telling such stuff they better should grab for the old blueprints redesign the mount and took the last series of Contax RF Sonnar back in series, honestly.

Obviously every f/1.5 lens of the world with a focal length of 50mm has the same DOF at a given distance. Every f/1.4 lens has the same (smaller). And every f/1.0 lens as well (smaller yet). It's just a matter of optical laws. Different values printed in specs are a matter of different "Zerstreuungskreis" (circle of confusion) calculated with.

The C-Sonnar I've got from Zeiss was in focus wide open at f/1.5 close and with excellent results but it wasn't that clear at infinity. I did five or six night shots handheld and possibly all were unsharp due to shake. I did not investigate that further because I had to give back the lens. All f/4 or f/5.6 shots infinity were very crisp, not dull what would have to be expected when focus isn't correctly aligned. But again, I didn't test that.

If the lens isn't in focus wide open either close-distance, at infinity or both, the RF cam of the lens has to be re-calibrated to perfect matching at *all* distances regardless the cost of the lens. With a close up distance of 0.9m this should be a task not needing a rocket scientist. If it's not possible the mounting is badly designed and the problem of the maker, not of the buyer. If Zeiss technicians oracle is referring to focus-shift (moving of best focus point when aperture is closed; this was a common error in stone age of large format cameras) the optics are badly designed.
 
Sonnar2 said:
If Zeiss technicians really telling such stuff they better should grab for the old blueprints redesign the mount and took the last series of Contax RF Sonnar back in series, honestly.

Obviously every f/1.5 lens of the world with a focal length of 50mm has the same DOF at a given distance.
Click to expand...
I guess the issue here is spherical aberrations, as sebastel pointed out, which lead to a more or less curved "plane" of focus at different apertures. Since these aberrations are aperture-dependent, the shape of the "plane" of focus would change with aperture. If I understand correctly, the creamy bokeh of the classic Sonnar type comes precisely from low correction of spherical aberrations, which is why OOF highlights look disc-shaped. While the C-Sonnar's design is not identical with the classic one, I guess the new design would have similar properties.

What I wonder is why Zeiss (supposedly) align their rangefinder lenses for accurate focusing at f2.8 in a f1.5 lens, because that way it would be absolutely impossible to focus accurately wide open. And I don't know where and how this guy focused. Given that the "plane" of focus is curved, the distance might actually be accurate in the center but not in the corners, so when the focus target is in a corner it might be missed by some amount.

The whole story is a bit strange. All in all, given the very limited amount of outcry so far about focusing problems with the C-Sonnar, I am nevertheless inclined to believe that something was wrong with the reviewer's lens.

Philipp
 
Hi Philipp,

if you think the special glow of the Sonnar is just under-correction of spherical aberration just take a look at the two curves at http://www.google.com/patents?vid=USPAT1975678&id=D_1oAAAAEBAJ&pg=PP1#PPP1,M1
showing the spherical aberration with higher aberrations for the older lens. I cannot remember any saying that the Sonnar's of the early 1930's producing nicer pictures compared to the later. Spherical aberrations alone wouldn't results in a more pleasent look.
More important it shows there is no way to compensate spher.ab. with the focussing helicoil because it tends to go to zero whith aperture closed, therefore the lens has to be designed to focus at the zero-point center of the picture where spher.ab. is zero even wide open, and don't bother with field or corner (un)sharpness for whatever aberration (spherical, coma) is responsible for.
Consequently, corner-DOF is the same as center-DOF, but SHIFTED behind with a lens of undercorrected spher.ab. This, in some motives like human faces, can increase the impression of DOF, and in most cases, background will look "less blurred" as with a lens with flat field. Again, DOF isn't measured in different or multiple points but in the center, and not any secrets or wisdom on design of particular lenses but just law of optics the lens maker has to follow.

cheers Frank
 
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There's an update of the test on LL:

"When the review of the 50mm Sonnar was first published there were some rather derogatory comments made on an online forum about our review, because of the concerns we had expressed about the sharpness (or lack thereof) of this lens when used wide open.
I had contact Zeiss about our finding and was told that the lens tested would be checked and also that the factory would be contacted for their feedback. Below is their response, confirming the appropriateness of our findings, and explaining why this is the case."​

The online-forum mentioned - is that our discussion here?​
 
i don't think intelligent discussion can be mistaken for derogatory remarks.

i just read the zeiss response and i don't get it.
on their site they call the 50/1.5 the photojournalit lens and on LL they say it is for artistic interpretations.

my copy seems just fine at 1.5, what i focused on was in focus in the end image.

i'm confused about the writings about this lens but not about the lens.

joe
 
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