Cv 35/1.4

[sreidvt]

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"This type of discussion is fascinating because it lays bare so many things. Ok, so there is a bad copy of a CV lens. Bad in what way?

 

- Bad because it didn't work well with the reviewer's camera as it is calibrated?

 

- Bad because it didn't conform to it's own manufacturer's specs?

 

- Bad because we expected tack sharp corner-to-corner performance and didn't get it?

 

- Bad because a fast lens has spherical aberration and focus shift?"

 

Hi Dante,

 

That's an interesting post. I have a few comments.

 

On your "bad" list you propose four reasons. I agree that 2 - 4 are interesting questions to ask. Regarding #1:My focus bracketing methodology essentially eliminates RF calibration, etc. issues *and* the CV 35/1.7, which did beautifully, was used on the same test body. So the body is fine and the methodology would compensate even if it wasn't.

 

"To say that Tom has a good copy and Sean has a bad copy is a guess - and however well intentioned, it is giving the manufacturer the benefit of a doubt it might not deserve.

 

The test for those of us who walk into a store (or get online) and buy a lens is whether a single example (ours) will plug into an M8 and work the first time. In that sense, Sean's test is conclusive: a single random sample."

 

Two samples for that review. Two more on the way.

 

"Does it work? Draw your own conclusion. I haven't looked at the results too closely, but if you don't like them, you have to brace yourself for the possibility that you will get that type of result."

 

That may be true.

 

"Tom's "good" copy, assuming the bulleted factors above, is another potential outcome. But it only brings the odds up to 1:1. And if it is a deviant production variation that coincidentally favors what people want in performance, it would not definitive evidence of anything."

 

Many people do not realize that Tom has not yet done (but may currently be doing) the tests I did. So we actually have no idea how his copy compares until we see the results of his focus shift and field curvature/res. tests. I've posted this before but I think some people are missing it. I hope people reading this now will note it. Tom and I spoke by phone recently about this. There's no reason *yet* to assume that Tom's copy performed any differently from mine. First his tests would need to be done.

 

"I would say that the only way to test lenses on an M8 is a have a body that is calibrated and hand-delivered (not air-shipped) from the factory, coupled with a single, randomly selected new sample of each lens from a distributor's stock."

 

I'm guessing you've never used focus bracketing for this kind of testing. Its much simpler than what you propose as it removes RF accuracy from the equation. I wish more people understood that. I don't think many reviewers use that methodology but its needed to remove confounding variables. In fact, any test of lens resolution that does not include a very careful focus bracketing methodology may be flawed. Its one of the most important steps in resolution testing.

 

"Or, optionally, you could collect a statistically valid sample (which will be a lot more than two) and measure the collimation variances and RF coupling variances to determine what is a "normal" copy of the lens, what the tolerance is, and then test accordingly. But that cuts out the part that is useful to the person who is going to buy one lens."

 

Again - much too complicated. Better to just use a focus bracketing methodology.

 

"But realistically, out of the box consistency between examples and build quality is what makes good lenses very expensive."

 

That is indeed one reason they cost so much. The consistency *should* then be better. Often it is but sometimes it is not.

 

"That's why you virtually never see these kinds of discussions with Leica lenses that cost six times as much. You are paying an insane price for microscopic tolerances, indestructible materials, and insanely good quality control."

 

I agree that this is less common with Leica lenses although there have been unfortunate exceptions despite the high cost. I'm not yet sure that the copies I tested were atypical.

 

Cheers,

 

Sean

[sreidvt]

Hi Nick,

 

Thanks. Speaking for myself, if all copies of this lens perform as did the two I tested, I don't want one. And, actually, I had planned to buy one for myself. In this price range, I think (so far) that the 35/1.7 has more to offer.

 

But...some photographers are probably going to end up doing excellent work with this CV 35/1.4, esp. at F/1.4 - F/2.0 or below F/5.6. And I always keep in mind that one lens I like a lot, the LTM Canon 28/2.8, performs terribly in most technical respects. So, I just try to describe things as well as I can and then let photographers make their own judgement call.

 

I suspect that other samples of this lens will confirm the focus shift. The corner res. may or may not be related to decentering. It's too soon to say.

 

Cheers,

 

Sean

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[sreidvt]

Sean, I also havent noticed any focus shift on my pre-asph 35mm Summilux. Flare is another story....

 

I haven't ever tested one carefully. Tom's comments were based on his own experience with that lens.

 

Cheers,

 

Sean

[dante]

Sean, I disagree that focus bracketing is a practical solution when the frame of reference is a lens and not an optical cell.

 

In a rangefinder system where focusing is blind, where the relative positions of the optical cell, the subject, the imaging plane, the lens reference surface, and the RF coupling of the lens must all be in the correct relationship, the mechanical parts of the lens itself cannot be ignored.

 

Focus bracketing eliminates the rangefinder element, but it also obfuscates the mechanical errors built into the finished lens. What good is a fast lens that has excellent theoretical resolution but is set in a mount that does not send the right signals to the rangefinder mechanism? When a mis-focus of 0.02mm at the film plane is enough to cost you half of your resolution on an M8 (or create an apparent focusing error of a few inches in the ultimate image), mount quality is a very critical element.

 

And if all we are worried about is the lens’ performance (“on its best day”), regardless of the camera platform, RF calibration, human eyesight or RAW developer, why not just use an MTF test? It’s far more objective, at least up to the diffraction aperture.

 

The other question that comes up with focus bracketing is whether can even be done consistently and with repeatability among different lenses. Although RF cam movement is always theoretically identical with all lenses from infinity to one meter (because it is tied to a "standard" 50mm lens and the lens focusing mount translates between the focal length of the lens and where a 50mm lens' cam would be), different lenses have different focusing ring twist rates, and when you get into wideangles, microscopic movements of the ring can mean big distances in focus. And these rings are not calibrated in any way that would be meaningful to rigorous technique; I think there is a legitimate question of overshooting or undershooting the intended bracket interval. I know this firsthand after working for about half a day on Saturday to compare the focus characteristics of my 35 Summilux ASPH against my 75mm Summilux to figure out whether the RF on my camera was off.

[fotografr]

Hi Sean, could be on your way a comparison between the pre-asph Summilux 35 and this new CV35?

Many of us have had (or still have) the pre-asph 35lux, so it could be somehow interesting to read your comparison with a well known subject;)

 

Isn't that the lens that doesn't work on the M8?

[blakley]

Hi Nick,

 

Thanks. Speaking for myself, if all copies of this lens perform as did the two I tested, I don't want one.

 

I suspect that other samples of this lens will confirm the focus shift. The corner res. may or may not be related to decentering. It's too soon to say.

 

Sean,

 

I've got a copy of the CV 35/1.4 SC and have noticed (but don't care much about) the focus shift. What really bothers me is the lack of resolution even on center wide open. It's also got some sort of "glow" reminiscent of veiling flare or coma (but probably not coma since it happens even on center) wide open. The glow is a pictorial element I can work with, but the low resolution is a very unwelcome surprise.

 

I'm going to work with the lens a while & see if I can coax a pictorial effect I like out of it, but I must admit to being disappointed.

[stunsworth]

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Isn't that the lens that doesn't work on the M8?

 

Brent, some Pre-ASPH Summiluxes work and others down. Mine is one of the ones that works.

 

The problem is caused by a sheath at the rear of the lens. The lens will mount, but not focus to infinity. Leica can fix this, so a copy of the lens with the infinity focus issue can be made to work.

 

The Pre-ASPH Summilux is however one of the lenses that Leica can't code for use with the M8. I haven't found this to be an issue in practice.

[sreidvt]

Sean, I disagree that focus bracketing is a practical solution when the frame of reference is a lens and not an optical cell.

 

In a rangefinder system where focusing is blind, where the relative positions of the optical cell, the subject, the imaging plane, the lens reference surface, and the RF coupling of the lens must all be in the correct relationship, the mechanical parts of the lens itself cannot be ignored.

 

Focus bracketing eliminates the rangefinder element, but it also obfuscates the mechanical errors built into the finished lens. What good is a fast lens that has excellent theoretical resolution but is set in a mount that does not send the right signals to the rangefinder mechanism? When a mis-focus of 0.02mm at the film plane is enough to cost you half of your resolution on an M8 (or create an apparent focusing error of a few inches in the ultimate image), mount quality is a very critical element.

 

And if all we are worried about is the lens’ performance (“on its best day”), regardless of the camera platform, RF calibration, human eyesight or RAW developer, why not just use an MTF test? It’s far more objective, at least up to the diffraction aperture.

 

The other question that comes up with focus bracketing is whether can even be done consistently and with repeatability among different lenses. Although RF cam movement is always theoretically identical with all lenses from infinity to one meter (because it is tied to a "standard" 50mm lens and the lens focusing mount translates between the focal length of the lens and where a 50mm lens' cam would be), different lenses have different focusing ring twist rates, and when you get into wideangles, microscopic movements of the ring can mean big distances in focus. And these rings are not calibrated in any way that would be meaningful to rigorous technique; I think there is a legitimate question of overshooting or undershooting the intended bracket interval. I know this firsthand after working for about half a day on Saturday to compare the focus characteristics of my 35 Summilux ASPH against my 75mm Summilux to figure out whether the RF on my camera was off.

 

Hi Dante,

 

It depends on what one is after. For starters, my focus bracketing steps are so small that they, initially, do not even move the RF patch. That, I think, is sufficient. If you have a different methodology that use and like better, I'd be glad to hear about it. Frankly, I suspect that many reviewers and testers don't even try to use a precise focus bracketing methodology and that introduces a huge potential confounding variable into their results. One major reviewer, who shall remain nameless, made some strong criticisms of the M8 at one point based, in part, on a picture that was out of focus.

 

If one wants to know what a lens is capable of (with respect to resolution), focus bracketing works well. It's not perfect but its about the best we can do.

 

There's enough slop in even the best RF systems, as you know well, that there's no way to test a lens and be sure that other copies of the lens (on other bodies) will focus properly. So, really, each photographer needs to test his or her lens on his or her camera body. What my res. test results can tell one, though, is what that model lens might be capable of. Its reference information essentially.

 

So, even if I have an M8 with a well-adjusted RF (and I do) I still can't guarantee to readers that their copies (of a lens model I test) will focus correctly on their camera bodies. But I can show them examples that say, in effect, here's what this lens might be capable of when it is focused right on the money.

 

I imagine you well know, and might agree with, the following.

 

In reality, most pictures are slightly out of focus (at the intended focus plane). But, in fact, it usually doesn't matter all that much. With AF systems we have AF mistakes to contend with. With RF systems we have mechanical play and our own eyesight as confounding variables. With manual SLRs, we have focus screen limitations, limitations with our eyesight, etc.

 

We cannot trust our eyes and our rangefinders to provide definitive peak focus for res. testing, even under the best of circumstances.

 

An aside...I imagine many here know who Dante Stella is but, for those who don't, he's been providing very interesting information about cameras and lenses for many years. I've enjoyed his writing on the older Canon RF gear, for example. His site is located at:Dante Featured Picture

 

Dante, I'm happy to continue discussing this. I think its worthwhile to question one's own methods and approaches as a way of refining them.

 

Cheers,

 

Sean

[sreidvt]

Sean,

 

I've got a copy of the CV 35/1.4 SC and have noticed (but don't care much about) the focus shift.

 

Thanks for that info. I've gotten a lot of reports from people who are seeing that focus shift as well.

 

When the first part of my review, of that lens, was published, there was much wailing and gnashing of teeth on another forum - it was all wrong, my M8 was at fault, there was a conspiracy to bring down Cosina, etc. - the usual nonsense.

 

I think that time will prove that my observations about those two lens samples and focus shift were quite correct. I also *suspect* that the shift is endemic to the design and not a result of sample variation but I'll know more when I test two more samples.

 

The real remaining question, in my mind, is this: "Is the corner softness that I saw a result of de-centering in those examples, field curvature or something else?" That's where tests of these other samples will be esp. interesting to me.

 

On center, the copies I test were decent wide open. Does your example show the same res. seen in the review (at F/1.4 and F/2.0)?

 

Cheers,

 

Sean

[Vieri]

I think that time will prove that my observations about those two lens samples and focus shift were quite correct. I also *suspect* that the shift is endemic to the design and not a result of sample variation but I'll know more when I test two more samples.

 

The real remaining question, in my mind, is this: "Is the corner softness that I saw a result of de-centering in those examples, field curvature or something else?" That's where tests of these other samples will be esp. interesting to me.

 

Sean

 

Hello Sean, I think you are right on on this being the most interesting question at this point - at least, I can say that this would be what interests me the most too. Actually, when the 1.4/35 has been announced it immediately caught my interested, though I assumed just when the lens' optical formula and design came out that it would have had some focus shift. I could live with it, but what really would put me off is bad QC on the centering of the lens, and/or non controlled (excessive) field curvature and/or whatever brings unwanted - by me at least - unevenness on the frame.

 

Any envisioned timeframe for the review to be completed?

 

Thanks, once more, for your work - as you know I really appreciate it.

[sreidvt]

Hello Sean, I think you are right on on this being the most interesting question at this point - at least, I can say that this would be what interests me the most too. Actually, when the 1.4/35 has been announced it immediately caught my interested, though I assumed just when the lens' optical formula and design came out that it would have had some focus shift. I could live with it, but what really would put me off is bad QC on the centering of the lens, and/or non controlled (excessive) field curvature and/or whatever brings unwanted - by me at least - unevenness on the frame.

 

Any envisioned timeframe for the review to be completed?

 

Thanks, once more, for your work - as you know I really appreciate it.

 

Hi,

 

I don't know yet. The other two lenses haven't arrived yet and I'm knee-deep in DP1 stuff right now. Then there are seven other articles in process. I just do the best I can.

 

Cheers,

 

Sean

[blakley]

The real remaining question, in my mind, is this: "Is the corner softness that I saw a result of de-centering in those examples, field curvature or something else?" That's where tests of these other samples will be esp. interesting to me.

 

On center, the copies I test were decent wide open. Does your example show the same res. seen in the review (at F/1.4 and F/2.0)?

 

I'm seeing the same center and corner resolution you're seeing in your review - but it surprises me that you think it's OK on center. The center performance at f/1.7 is to my eye clearly inferior to the Ultron in the review samples you posted. This was the problem I observed in my early photos, though it took me a while to decide that what I was seeing was partly a resolution problem and partly some other phenomenon (veiling flare?). My initial impression was just that the image was "soft" all over including center.

 

I thought initially that it might be a decentering problem - so I'll look forward to your observations about that going forward.

[blakley]

Thanks for that info. I've gotten a lot of reports from people who are seeing that focus shift as well.

 

When the first part of my review, of that lens, was published, there was much wailing and gnashing of teeth on another forum - it was all wrong, my M8 was at fault, there was a conspiracy to bring down Cosina, etc. - the usual nonsense.

 

I think that time will prove that my observations about those two lens samples and focus shift were quite correct. I also *suspect* that the shift is endemic to the design and not a result of sample variation but I'll know more when I test two more samples.

 

Just to provide a little more evidence, I shot a few frames of the focus test chart with my CV 35/1.4 SC Nokton. This is very unscientific; I shot these photos handheld from close to closest lens focus and did not focus bracket any shot. Still, the shift evident in the photos is too large to explain as a result of errors in technique. The first shot shows the full frame; the next four are crops of the center of the focus test chart; in order they were taken at f/1.4, f/2, f/2.8, and f/4. All shot with filter on AWB in DNG at ISO 640 and autoexposure.

 

In order, the point actually in focus looks to me like "Spot on with veiling flare" at f/1.4, "about 14mm behind point of focus, still with veiling flare" at f/2, "about 30mm behind point of focus" at f/2.8, and "about 50mm behind point of focus" at f/4. The mm measurements are read straight off the chart but should not be presumed to be accurate because I wasn't shooting at exactly 45 degrees.

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[sreidvt]

Hello Sean, I think you are right on on this being the most interesting question at this point - at least, I can say that this would be what interests me the most too. Actually, when the 1.4/35 has been announced it immediately caught my interested, though I assumed just when the lens' optical formula and design came out that it would have had some focus shift. I could live with it, but what really would put me off is bad QC on the centering of the lens, and/or non controlled (excessive) field curvature and/or whatever brings unwanted - by me at least - unevenness on the frame.

 

Any envisioned timeframe for the review to be completed?

 

Thanks, once more, for your work - as you know I really appreciate it.

 

Hi,

 

I don't know yet. The other two lenses haven't arrived yet and I'm knee-deep in DP1 stuff right now. Then there are seven other articles in process. I just do the best I can.

 

Cheers,

 

Sean

[sreidvt]

Just to provide a little more evidence, I shot a few frames of the focus test chart with my CV 35/1.4 SC Nokton. This is very unscientific; I shot these photos handheld from close to closest lens focus and did not focus bracket any shot. Still, the shift evident in the photos is too large to explain as a result of errors in technique. The first shot shows the full frame; the next four are crops of the center of the focus test chart; in order they were taken at f/1.4, f/2, f/2.8, and f/4. All shot with filter on AWB in DNG at ISO 640 and autoexposure.

 

In order, the point actually in focus looks to me like "Spot on with veiling flare" at f/1.4, "about 14mm behind point of focus, still with veiling flare" at f/2, "about 30mm behind point of focus" at f/2.8, and "about 50mm behind point of focus" at f/4. The mm measurements are read straight off the chart but should not be presumed to be accurate because I wasn't shooting at exactly 45 degrees.

 

It's increasingly looking like the world is round, even in my scandalous CV 35/1.4 review! <G>

 

Cheers,

 

Sean

[Dan States]

To be fair to Cosina, the lens is marketed as a "classic" and I don't think they claim it to have perfect technical qualities. The Sonnar 50F1.5 is all the worse because it starts out with even less depth of field to mask focus shift, yet it often gets described as "artistic" in it's rendition when it's just plain out of focus. Zeiss trotted out their marketing double talk about the Sonnar only after Luminous Landscape and numerous early users (including me) starting squealing about focus problems.

 

I can't see how lenses with this kind of aberration can survive in the era of instant 100% digital magnification. It takes a pretty high level of rationalization to accept an optical flaw that is so easy to verify.

 

Best wishes

Dan

[sreidvt]

To be fair to Cosina, the lens is marketed as a "classic" and I don't think they claim it to have perfect technical qualities.

 

Indeed, I agree with this sentence. And, with it in mind, people need not panic or cry foul when a review reveals these qualities to be what they are (in these two samples so far).

 

Cheers,

 

Sean

[Dan States]

Sean, wouldn't it be interesting to put the "sample variation" bug bear to bed by testing say, 10 copies of a lens for focus shift. I'd wager that if any copy has this fault they ALL do and claims otherwise are due to variations in test technique, not manufacturing tolerances.

 

Certainly off center elements and flare are often one off faults, but focus shift is a basic element of a lens design and the tradeoffs made by the designers. What is needed is some kind of measurable standard within which digital users can be confident in their exacting results. I'd guess you would find that shift measured as a percentage of depth of field would be an easy way to compare this aberration. IE: The Sonnar F1.5 has shift of X% of it's depth of field at X aperture.

[sreidvt]

Sean, wouldn't it be interesting to put the "sample variation" bug bear to bed by testing say, 10 copies of a lens for focus shift. I'd wager that if any copy has this fault they ALL do and claims otherwise are due to variations in test technique, not manufacturing tolerances.

 

Certainly off center elements and flare are often one off faults, but focus shift is a basic element of a lens design and the tradeoffs made by the designers. What is needed is some kind of measurable standard within which digital users can be confident in their exacting results. I'd guess you would find that shift measured as a percentage of depth of field would be an easy way to compare this aberration. IE: The Sonnar F1.5 has shift of X% of it's depth of field at X aperture.

 

I'll end up testing two more samples and that will do it for me. Its an interesting lens but I have a lot to cover this spring.

 

Cheers,

 

Sean

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Hallo,

Look here: Leica M

[Mauribix]

Sure, I'd be happy to include it if someone wants to send me a copy to test. I've used one but don't own one.

 

Cheers,

 

Sean

 

 

Ouch!

I had one of the latest copy of that lens (a titanium finish one), but i sold it few months ago... I will try to investigate about tha availability of one of those within my friends.