Very interesting answer from Leica on 35mm 1.4

[innerimager]

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Hi Peter,

 

My methodology is made clear in these shots. The setup remained the same (shot one) throughout with the camera mounted on a tripod and point of focus unchanged throughout, on the 20cm mark which was in line with 'Canon' on the box, which is what I focussed on using a 1.25 magnifier. The only changes between shots were stopping down one full stop at a time.

 

So the tripod means that there's no need to refocus and indeed since the camera does not know the F stop it would be pointless to refocus.

 

Any thoughts?

 

Tim

 

ps Solms has answered my detailed query by suggesting I buy an Elmarit 28 f2.8 because 'is not affected by spherical aberration at all'.

Yes Tim- First, they are right in that the 28 elmarit is sharp as a tack! But as to the 35/1.4- I would ask you to repeat this test, but this time, actually refocus after each aperture adjustment. I predict the results will be different. I am far from expert at the optics here, but the range of angles of light waves does vary with aperture adjustment with aspherical lenses. I believe that by placing your exact point of focus each time you stop down, you will get better results, at least I hope so. best....Peter

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[AlanG]

Clearly your lens has a focus shift when stopping down on images of close subjects. Maybe test it for more distant subjects too. (Center and edge)

 

But this should be problematic only on short distance shots, as Alan G noted. At ten meters, the depth of the sharp area is more than ten times greater than what you get at 1 meter, so I think that the problem you see is of different nature, and that the generic and theorical reply you got from Solms is not applicable.

 

I agree. You may be confusing what Leica says about the center and edge rays with center and edge sharpness. Even if the plane of focus is shifting due to spherical aberrations it should still be possible to get a sharp image corner to corner. Unless the lens design or assembly is poor which of course it shouldn't be. So we may be discussing two seperate issues - focus shift when stopping down due to sperical aberrations, and lack of a flat field (that may change due to stopping down.)

 

I will say that I bet Leica does not think of a 35 1.4 as an ideal lens for architecture (sharp flat field with low distortion.) Keep in mind that the specialized wide view camera lenses I use are f4.5 and f5.6 wide open. They generally need to be shot at f11 or smaller for excellent results. And a center filter is often used to reduce vignetting. So to expect any manufacturer to overcome all of these conflicting design factors - speed, distortion, minimal vignetting, flat field, C/A, etc. in one lens is asking for a lot. Requiring a lens to be fast is probably the biggest compromise although no 35mm manufacturer seems interested in making small very well corrected slow wide angle lenses. That being said, Leica's site claims the 35 1.4 has an excellent flat field, and more...

 

I found this to be a pretty good explanation of spherical aberation:

 

Spherical aberration

[Jamie Roberts]

Hi Tim,

what I see in your test is very similar to the results I get from the 35 cron asph, with a small difference. My lens full open fronfocuses more (about 3 cm, as if the Canon was at the 23 cm mark) . This leaves more space to the change of the focus plane position stopping down, when this plane shifts back. I think this is the correct adjustement to compensate for the focus shift to mantain the subject in the focus area.

 

Sergio--

 

I think you've nailed this. Tim; I think you have a backfocus problem!

 

D'uh. But What Sergio is describing is closer to what I saw when the camera was adjusted properly... a little more "front room" wide open than "back"--and that probably accounts for the annoying back focus at f4.

 

So you may not have had two defective lenses; your M8 might just need a slight adjustment, that you may be able to do yourself. Beats a trip to Solms, anyway! Give it a try!

[carstenw]

Yes Tim- First, they are right in that the 28 elmarit is sharp as a tack! But as to the 35/1.4- I would ask you to repeat this test, but this time, actually refocus after each aperture adjustment. I predict the results will be different. I am far from expert at the optics here, but the range of angles of light waves does vary with aperture adjustment with aspherical lenses. I believe that by placing your exact point of focus each time you stop down, you will get better results, at least I hope so. best....Peter

 

Peter, aren't you thinking of SLRs, where you actually look through the lens? What difference could it possibly make on a camera which can barely tell that there is anything there at all?

[tom0511]

it's funny how we talk about front and back focus with our new leica M8. I don't remember there were any discussions on FF and BF on film M cameras. I think Leica should put a disclaimer that you will see a slight OOF when images are blown up to 100% like we all do on our computer screen nowadays. I think Canon did that with their products awhile back. FF and BF problems are common problems among DSLRs as well.

 

About 12 years ago I sold my 90/2.8 because it was not focusing correct on my M6.

today focus problems are more obvious and easier to detect, but its not a new thing.

[innerimager]

Peter, aren't you thinking of SLRs, where you actually look through the lens? What difference could it possibly make on a camera which can barely tell that there is anything there at all?

Carsten- and Tim- as I reflect on your question, you must be correct. Years of DSLR use clouded my months of RF understanding. There is no way the range finder is influenced by the aperture. Sorry about that, even sorrier about the implications! best...Peter

[peterv]

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Carsten- and Tim- as I reflect on your question, you must be correct. Years of DSLR use clouded my months of RF understanding. There is no way the range finder is influenced by the aperture. Sorry about that, even sorrier about the implications! best...Peter

 

Nevertheless, Peter has a point I think...

 

Agreed, if the focus ring is left untouched, while changing the aperture, everything is fine... But just to be safe, and since it doesn't - or shouldn't - matter, it would be advisable to refocus to make sure you didn't accidently touch the focus...

[marknorton]

Tim, I'm interested in trying to reproduce your results on my own 35/1.4, what's the distance between camera and your Canon lenshood box?

[sean_reid]

Carsten- and Tim- as I reflect on your question, you must be correct. Years of DSLR use clouded my months of RF understanding. There is no way the range finder is influenced by the aperture. Sorry about that, even sorrier about the implications! best...Peter

 

I was just going to mention that myself. The RF mechanism has no awareness of aperture at all so refocusing after stopping down wouldn't do a thing.

 

Cheers,

 

Sean

[tashley]

Tim, I'm interested in trying to reproduce your results on my own 35/1.4, what's the distance between camera and your Canon lenshood box?

 

 

Hi Mark,

 

Plus or minus a millimeter or two the distance between the Canon logo and the sensor was one meter. I would be extremely interested in your findings since both my samples have been returned to Solms and I can't do it myself!

 

If this inquiry expands I could post a couple of extraordinary shots taken within moments of each other on the 35 lux and the 50 lux, which appear to show that the 35 lux loses focus about a third of the way from the edge and then regains it at the edge and centre.

 

This all sounds very nit picky, but I think there are issues here that we need to bottom out. Can a 35mm with a huge aperture be made so as to not backfocus with aperture stopdown? Does Asph make it worse (and so should we be buying older non asph lenses?) Are (gasp) any of the Zeiss or CV alternatives better? Should we just buy f2 or 2.8 lenses at this focal length? Did I get a bum lens or is this a necessary characteristic given the physics?

 

As the British satirical magazine Private Eye has stated for many years now:

 

I think we should be told!

 

Tim

[tashley]

I was just going to mention that myself. The RF mechanism has no awareness of aperture at all so refocusing after stopping down wouldn't do a thing.

 

Cheers,

 

Sean

 

 

Hi Sean

 

I was very glad to see that you'd caught this thread - my redux so far is that more people than not (self selection survey caution taken!) have this problem than not, and I suspect it to be endemic. Not Leica's fault, probably due to the physics of light etc, but that's how it looks. And in effect this is what Leica said. If someone else can run a similar test on the lens and show that the wide open POF remains in focus throughout the aperture range then I'll just keep trying samples til I get a 'good one' but I suspect that those few who think they have a good one have not looked closely!

 

You're the man to bottom this out. Roll on your 35mm reviews!

Tim

[tashley]

Nevertheless, Peter has a point I think...

 

Agreed, if the focus ring is left untouched, while changing the aperture, everything is fine... But just to be safe, and since it doesn't - or shouldn't - matter, it would be advisable to refocus to make sure you didn't accidently touch the focus...

 

 

I promise you, 100% certain, that the focus ring did not get touched. I was very careful. I even took each shot on a time delay so as to ex-out shake totally, and the tripod was a manfrotto the size of a man....

 

Tim

[tashley]

OK, so all this is about expectations. My 50 lux is almost miraculous in its ability to achieve selective focus. I took this one just before Christmas at dinner with friends when I was not totally sober BUT I am good at focusing this lens. My point is that I'd like a 35mm 1.4 that can do this degree of accuracy wide open in very low light...

 

ISO 640, 1/20th sec, RAW in LR... and I focussed on his left (your right) eye. The corner where the lines are.

 

T

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[Jamie Roberts]

{snipped}My point is that I'd like a 35mm 1.4 that can do this degree of accuracy wide open in very low light...

 

ISO 640, 1/20th sec, RAW in LR... and I focussed on his left (your right) eye. The corner where the lines are.

T

 

Tim--

 

Now I'm really confused. I thought your 35 1.4 *did* focus properly wide open. Now you're saying it doesn't?

 

Let me just ask directly: have you adjusted your m8 for backfocus yet? You should.

 

My 35 1.4 focusses just fine between f1.4 and f8 on objects like you're showing. Yes--DOF shifts because of focus shift; but the thing you're focussing on should actually be in focus.

 

If it isn't, then I believe it's your camera--not the lens--needs adjusting, most likely. The fact that you've gone through two of them means it's even more likely to be the camera.

 

Here's the 35 f1.4 @ f1.4...and it was also fine that day at f4 and f8. Straight out of C1, focussed on her right (viewing left) in-shadow eye.

 

It's tack sharp, but it's quite close to the back of the existing focal field, not the front (in fact, the lens is close to front focussing a bit, but not).

 

That's ok; I like the tips of people's noses and their mouths actually in focus; I don't care so much about their ears wide open like this.

 

As I stop down, the focus field shifts to a classic 1/3 front 2/3 back sort of DOF (as someone else mentioned, I think). So while the focal field changes, the focus point does not (or at least it looks ok to diffraction limit, and then it's in focus but not as sharp anyway).

 

IOW, it focusses just fine, but you'll probably need to adjust the camera a bit. I don't think much more mysterious is going on here; your focus plane is just a little off is all, and it gets exacerbated when you stop down.

 

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[tashley]

Tim--

 

Now I'm really confused. I thought your 35 1.4 *did* focus properly wide open. Now you're saying it doesn't?

 

Let me just ask directly: have you adjusted your m8 for backfocus yet? You should.

 

My 35 1.4 focusses just fine between f1.4 and f8 on objects like you're showing. Yes--DOF shifts because of focus shift; but the thing you're focussing on should actually be in focus.

 

If it isn't, then I believe it's your camera--not the lens--needs adjusting, most likely. The fact that you've gone through two of them means it's even more likely to be the camera.

 

Here's the 35 f1.4 @ f1.4...and it was also fine that day at f4 and f8. Straight out of C1, focussed on her right (viewing left) in-shadow eye.

 

It's tack sharp, but it's quite close to the back of the existing focal field, not the front (in fact, the lens is close to front focussing a bit, but not).

 

That's ok; I like the tips of people's noses and their mouths actually in focus; I don't care so much about their ears wide open like this.

 

As I stop down, the focus field shifts to a classic 1/3 front 2/3 back sort of DOF (as someone else mentioned, I think). So while the focal field changes, the focus point does not (or at least it looks ok to diffraction limit, and then it's in focus but not as sharp anyway).

 

IOW, it focusses just fine, but you'll probably need to adjust the camera a bit. I don't think much more mysterious is going on here; your focus plane is just a little off is all, and it gets exacerbated when you stop down.

 

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Hi Jamie, and thanks for the example. To clarify: the shots of the chappie above were taken on my 50mm lux, not on either of the 35 luxes. I posted it so as to indicate that I'd like to be able to at at least one bit of the image really sharp (in this case the eye) but I didn't make myself clear in my text as to what I meant.

 

To be 100% clear:

 

My 50 lux has perfect focus and the point of focus remains in focus throughout the F stop range.

 

The 35 luxes I've tried do focus accurately at f1.4 ( though are slightly soft there, I don't mind that, and anyway they're known for it). However as you stop down, (see the examples with the ruler I posted above) the point of actual focus shifts backwards from the point of selected focus such that between (and including) F2 and F8 the object on which I originally focussed is to varying degrees OOF. At smaller F stops still the object regains focus as DOF improves.

 

Methodology is described in the post I refer to but involves

 

* a tripod

* self timer release for every shot

* an untouched focus ring after initial focus for the first shot

* a ruler in the FOV

and so on.

 

In other words I have X'd out all other factors comprehensively. Including the possibility that my M8 itself backfocusses, because other lenses put through the same test pass happily.

 

In other words I am 100% certain that the lens is impossible to focus, using an accurately calibrated RF, between f2 and f8, without guesswork to adjust for backfocus. The fascinating question for me is whether anyone actually has an example that DOES focus accurately here.

 

With the best respects we can't tell that from your portrait: all we know is that it's lovely and that her eye is in focus. I have shots from the 35 that are in focus too, at mid apertures, but they are so but accident. I swayed or the subject moved or I didn't focus with great accuracy, whatever. But if I test it empirically under controlled circumstances, it fails every time... and if you had a few minutes I would LOVE to know what happens when you run a similar test. Then I'd know if I should keep searching for a good 'un or give up!

 

Best

 

Tim

[carstenw]

Tim, there is one possibility: your M8 is not quite calibrated, but the error is small enough not to disturb your less sensitive lenses. (The 50 Lux has a floating element, so it may well be that Leica had a little more flexibility to reduce the focus-shift with that lens.) The 35 Lux has a slight focus shift which doesn't normally cause out-of-focus images, but combined with your M8, it does. This possibility would seem to explain why your results are a little different than others here. I would send the M8+35 Lux to Solms together.

[tashley]

Tim, there is one possibility: your M8 is not quite calibrated, but the error is small enough not to disturb your less sensitive lenses. (The 50 Lux has a floating element, so it may well be that Leica had a little more flexibility to reduce the focus-shift with that lens.) The 35 Lux has a slight focus shift which doesn't normally cause out-of-focus images, but combined with your M8, it does. This possibility would seem to explain why your results are a little different than others here. I would send the M8+35 Lux to Solms together.

 

Thanks Carsten - that does sound like a possibility though my tests with other lenses were very satisfactory to the extent that if it wasn't for the question of the 35 lux I wouldn't even think of checking the RF calibration. But I know you know this stuff, so I'll maybe do that!

 

Tim

[jonoslack]

Thanks Carsten - that does sound like a possibility though my tests with other lenses were very satisfactory to the extent that if it wasn't for the question of the 35 lux I wouldn't even think of checking the RF calibration. But I know you know this stuff, so I'll maybe do that!

 

Tim

Sounds like a recipe for frustration to me - you send it to Solms, it's away for 6 weeks, and I bet you ten bob that one of two things will happen.

 

1. it'll work properly with the 35mm . . . . but not with anything else

2. it won't be any different and they'll say it's 'within tolerance'

 

But then - I always was a cynical old so and so!

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[carstenw]

If you don't have a backup camera, then 6 weeks is a very real risk... What I might do myself (if I cannot think of a proper way to adjust the eccentric on the arm) is to bite the bullet and send the camera to one of the independents who do this kind of work. There is one in Holland, one in Germany and one in Italy, and probably more. With a proper arrangement, it would probably take less than a week, although it would not be free.

[marknorton]

I've now repeated Tim's test with my 35/1.4 and a couple of M8s and get broadly similar results, if not quite as extreme. I find the point I've focussed on stays in focus as I stop down and the increased depth of field extends only away from the camera with little or nothing towards the camera.

 

I think it will help, when shooting with this lens stopped down to focus a little closer than if you were shooting wide open.

 

The 35/1.4 was one of the first lenses to use the concave front lens design and is now 13 years old, so it might be time for a makeover.