Old Sonnar focus shift (is it just Zeiss spin?)

[Dan States]

Zeiss has been making the claim that all Sonnar lenses have focus shift and that we just never noticed it until the ZM because the new ZM is SO darned good it just makes it easier to see. I started thinking about the thousands of images I've made with old Sonnars. WAS this something I just never noticed? I suspected it in my Sonnar F2. (It always seemed sharper at infinity than where I was focusing, but my F1.5 always seemed pretty darned sharp and easy to focus.)

Tonight I decided to see if I could induce visible focus shift in two classic Sonnar lenses. In the end what I found was suprising, but first the details:

I made test shots at full aperture and two stops down on both lenses using table mounted and clamped camera. Both lenses are in outstanding condition and my IIA was serviced by Henry Scherer and it is in near mint condition. I used Plus X film developed in D76. Not the sharpest combo, but it's what I use in the real world and that's what counts.

Results: At 6 feet from the target the Sonnar 1.5 showed no visible shift of focus between F1.5 and 2.8. As expected the lens performance improves but the plane of focus remains fixed enough not to be noted in a 3200dpi scan at 100% magnification.

The Sonnar F2 DID show some shift of focus between F2 and F4. HOWEVER, this shift was not enough to throw the point of focus out of the typical depth of field. In any normal sized print up to say, 12x, you just would not see the effect.

Note that I did these shots at longer distances than we are seeing in most tests on the net because my experiences with the ZM Sonnar indicate it has very visible shift at LONGER distances. Even at 5 meters the ZM Sonnar shift is greater than the standard depth of field.

In the attachements the first two shots are from the 1.5 at full aperture and F2.8. The third is from the Sonnar F2 at F4. The point of focus on all images is the viewfinder of the M6.

 

[Dan States]

As I can only attache 3 images per message here is the Sonnar F2 at full aperture.

 

[awilder]

I agree from your images that the older Sonnars have little to no significant focus shift. I also believe that the current focus shift phenominon is not limited to minimum focus as most seem to stress now, but affects the entire range of focus since the culprit is undercorrected spherical aberration. One possible explanation might be a trade off in aberration correction. I base this hypothesis on an article by Peter Hennig shown in this link: http://www.rangefinderforum.com/forums/attachment.php?attachmentid=56014&d=12032...
Note the drastic difference in distortion. Your version from 1932 is shown to have up to 3% pincushion distortion while the currrent version has a little over 0.5% distortion.

 

[varjag]

Notice that in first sample photo the quality is so poor that you can't really pin down the focus point.

General fuzzy look and low contrast make it hard to see the shift, but it's there. You can't have such amount of spherical aberration as in classic Sonnar and no focus shift. If it seems there is none, the experiment or measurement must be flawed.

 

[rxmd]

I used Plus X film developed in D76. Not the sharpest combo, but it's what I use in the real world and that's what counts.

Excuse me for the harsh words, but if in the real world your pictures look as blurry as the first one, then focus shift is really the last of your worries. This picture allows no conclusion at all of what happens in the lens.

Try to get a series of sharp, in-focus pictures with a ruler in them and an easily identifiable focus target so that we can actually get an impression of what happens.

Philipp

 

[Dan States]

As noted above these are massive magnifications. Anyone who owns a Sonnar 1.5 can tell you they are wispy at full aperture. Not sure how you could fail to see the point of focus relative to the camera placed 4 inches behind.

 

[Dan States]

Notice that in first sample photo the quality is so poor that you can't really pin down the focus point.

General fuzzy look and low contrast make it hard to see the shift, but it's there. You can't have such amount of spherical aberration as in classic Sonnar and no focus shift. If it seems there is none, the experiment or measurement must be flawed.

I think you just made my point. There may well be SOME focus shift in the Sonnar 1.5, but you can't SEE it in normal sized prints because it falls within accepted norms of deph of field at a given print size. You can see the shift of focus in the ZM at 5x enlargement because it's much greater, exceeding depth of field.

I've been using the 1.5 for years in all kinds of motifs and have NEVER noticed any changes in plane of focus.

 

[rxmd]

As noted above these are massive magnifications. Anyone who owns a Sonnar 1.5 can tell you they are wispy at full aperture. Not sure how you could fail to see the point of focus relative to the camera placed 4 inches behind.

Your focus target is useless. All I see is that the second one is sharper because it's stopped down, but it's impossible to say precisely *where* focus is. Two targets spaced 4 inches apart at 6 feet are smack within DOF for a 50mm lens at f/2.8. There is no way you can detect focus shift with this setup.

Your argument about the film making it difficult to see where sharpness is boils down to that the film makes it difficult to see sharpness *in general*. Is this what you want to say? Then it doesn't really matter what lens you use as long as your film is blurry enough, which is an interesting, if slightly unconventional approach to photography 😉 Wispy has nothing to do with it, it's just that a crispy film helps when testing sharpness issues.

Do the same thing at 90 cm or so, i.e. as close as you can get. Pin a needle vertically into a piece of wood and place a ruler diagonally behind it, so that at least 5 inches of ruler are visible either way. Use the crispiest film you can get. I find the experiment interesting. I'm not saying focus shift is or isn't there with the old lens, I'm just saying that with this setup it will be hard to find out.

Philipp

 

[rxmd]

There may well be SOME focus shift in the Sonnar 1.5, but you can't SEE it in normal sized prints because it falls within accepted norms of deph of field at a given print size.

Might well be the same with the ZM Sonnar. There is a technical issue, but it got blown out of proportion by people who looked at 10x enlargements of diagonal bookshelves on the Internet and said "but this is unacceptable".

When subjected to the same kind of testing, a Nikkor 50/f1.4, a Jupiter-3 or a Zeiss Sonnar 50/f1.5 might well show the same behaviour, it's just that people never bothered to test them as rigorously. In that respect your thread here is a step in the right direction.

However whether the whole thing matters in real-world photography is another question. Might well be that it doesn't with either lens for some people.

Philipp

 

[ferider]

The difference between the new ZM Sonnar and older Sonnar variants is that with the older lenses, the focus plane "smears out" when opening up from f2 to f1.4. I have shown these before but here they are again. Nikkor 50/1.4 at f2:

Nice and crisp plane of focus.

At f1.4:

Same film, same light, camera, etc. And where would be the plane of focus ?

The ZM lens on the other hand has a very well defined focus area, even at f1.5 (due to different glass and one more element, I guess). I refer to ruler shots taken by other people, but if you insist I have some, too 🙂

In practice, if you don't shoot rulers, it doesn't matter much anyways. Because even with the older Sonnars, and the "smeared out" focus plane, one can get great portraits:

This was taken with the same Nikkor as the test photos above, wide open and very close (uncropped). The loss of resolution didn't matter to me - my daughter's eyes sparkled enough 🙂

Roland.

 

[awilder]

Great shot of your daughter Roland! The plane of sharpness is spot on where it should be.

 

[Sonnar Brian]

I've shot with a number of post-war Sonnars made by Zeiss, Nikon, Canon, and FSU for quite a few years. I've never noticed much in the way of focus shift. Most of my lenses are optimized for close-up and wide-open. I recently picked up my first pre-war CZJ Sonnars. The focus shift in the 1935 5cm F1.5 seemed more pronounced that the younger lenses. I've not done a serious test, but it is one of the few lenses that required a couple of trips back to the table for collimation.

 

[WoolenMammoth]

I have an old 1.5 sonnar opton and a new zm sonnar and while the lenses exhibit very very different looks wide open, the old lens does not shift the way the new lens does and no, its not because I dont notice it... In practical use, shooting people with eyeballs, the focus shift of the new lens is much more of a bear to deal with than the old opton. Ive been using both consistently for months and months to base my opinion on...

 

[Dan States]

I wonder how hard it would have been to just duplicate the original Sonnar F1.5 exactly? Would have eliminated all this trouble.

 

[Sonnar Brian]

In that case, Why not just buy an Old Sonnar in the first place? It would be a lot cheaper!

I'm sure the new one is sharper. But the 1935 CZJ Sonnar is quickly becoming a favorite.

 

[WoolenMammoth]

totally different lenses. Same idea, but when you look at portraits shot with both at the same stop side by side, they are very very very different, the new one is waaay sharper. both awesome in their own right. Im comparing the new zm to a sonnar opton version. If you know the new 50mm Elmar-m vs. the old 2.8 elmar, the difference is well more pronounced than that. Having both is not redundant at all...

 

[jerkmam]

i have a canon 1.4, i am looking for a lenes that is good at 8. 5.6 .4,2.8. wood the new zeiss sonnar1.5 do,the job .the look of 60,s is what i need

 

[ampguy]

maybe if you scale focus

maybe if you scale focus

If there were ever a lens that should be fixed focus, or maybe 3 focus options: face, body, and mountain, this one seems to be it.

i have a canon 1.4, i am looking for a lenes that is good at 8. 5.6 .4,2.8. wood the new zeiss sonnar1.5 do,the job .the look of 60,s is what i need