Very interesting answer from Leica on 35mm 1.4

[mjh]

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The plot thickens and the mystery grows. Hmmm!

There wouldn’t be any mystery about this if it weren’t for the fact that some 1.4/35 Asph. don’t seem to show this effect. After all, it is an established fact that the 1.4/35 Asph. is suffering from some residual spherical aberration; also, it is well known that lenses with under- or overcorrected spherical aberration exhibit a slight focus shift when stopping down. So the focus shift observed by you (and others) doesn’t come unexpected – it’s the failure to observe this phenomenon with some apparently identical lenses that is truly puzzling.

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[sergiolov]

This entails compromising focusing accuracy at f1.4, where it is most critical – not an acceptable solution in my view.

 

You are right, my concept needs to be made more clear. Usually the focus area extends 1/3 in front of the subject and 2/3 in the rear. To keep the subjet allways in focus with a lens that shift focus back when closing it, it is necessary to position it in the center of the focus area, or a slightly forward position with respect to the center, so that shift is compensated by the wider rear space and increasing depth of field while stopping down.

If you take a look to the test images,this should clearly appear.

(due to my poor english, I have some difficoulty with complicated concepts, but I count on the forgiveness of forum members)

Sergio

 

Reading now your last post. All 35 asph have focus shift when stopped down,even the cron shows it. So the problem is either a defective lens, or a slight focus calibration is required for the camera, the lens, or both.

[mjh]

Usually the focus area extends 1/3 in front of the subject and 2/3 in the rear.

This is only true for one distance setting and wrong for all the others. At close distances the ratio is more like 1:1 and at the hyperfocal distance and beyond it is 1:infinity. Optimizing focusing on the assumption of a DOF ratio of 2:1 will not work in the general case.

[ChrisC]

Chris, it's there......

 

Mark - The article page is there, the download-able chart is withdrawn.

 

................Chris

[marknorton]

I downloaded a 19 page PDF this morning and the chart is page 18... unless it's changed since then?

[sergiolov]

This is only true for one distance setting and wrong for all the others. At close distances the ratio is more like 1:1 and at the hyperfocal distance and beyond it is 1:infinity. Optimizing focusing on the assumption of a DOF ratio of 2:1 will not work in the general case.

 

Infinity is an abstract concept, in practical photography it is a finite distance starting at approx. 1000xfocal lenght. What is important is that the focus plane,changing position in relation to the fstop, stays well inside the acceptable depth of focus.

If you take a look at the images of the focus test of the cron asph I posted, You'll see that it works.

[tashley]

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One of the advantages of a digital camera is the ability to chimp and adjust the results in a controlled or studio environment. In candid or street conditions its gonna be hit or miss.

 

That D70 article is interesting reading.

 

 

What I found was that chimping revealed the problem, by which time the opportunity had too often moved on!

 

Tim

[Jamie Roberts]

Infinity is an abstract concept, in practical photography it is a finite distance starting at approx. 1000xfocal lenght. What is important is that the focus plane,changing position in relation to the fstop, stays well inside the acceptable depth of focus.

If you take a look at the images of the focus test of the cron asph I posted, You'll see that it works.

 

I think Sergio is precisely describing the effect here.

 

My RF is fully focussable on the 24 2.8, the 28 2.8, 35 1.4, and 50 1.4 right now with the point of focus in focus throughout the field range.

 

I've got a really busy weekend, but I'm going to re-shoot one more time with the new chart.

 

My own ruler test, though, says the difference here is either 1) the RF adjustment--as I said, wide open this is almost (but not quite) front focussing or 2) some tolerance difference in the chrome vs black version.

 

I think it's the former Tim.

 

Here are some shots from my test (not pretty, but like I said I'll redo later today with the "Nikon" test (which is quite nice, btw--at least for close focus).

 

My three-year old was running around me while I was doing this; there may be some floor shake, even with a tripod (not kidding, and that's why I want to re-do these)

 

The focus point is the solid ruler bar before "news." IS0 1250:

 

f 1.4

Welcome, dear visitor! As registered member you'd see an image here…

Simply register for free here – We are always happy to welcome new members!

 

f 2.8

 

f 4

 

f 5.6

 

F8 and f11 were also in focus at the line and before the line. But you can see the field shifting towards the back of the ruler as the lens stops down.

 

More tonight--and I'll post right from 1.4 to 11 (bigger steps in between).

[mjh]

Infinity is an abstract concept, in practical photography it is a finite distance starting at approx. 1000xfocal lenght.

In fact I was referring to mathematical infinity here. Anyway, my point was that the popular assumption that “the focus area extends 1/3 in front of the subject and 2/3 in the rear” is generally wrong (see Misconceptions in photographic optics for an explanation).

 

If you take a look at the images of the focus test of the cron asph I posted, You'll see that it works.

It may work for the Summicron, but we are talking about the Summilux here.

[tashley]

I think Sergio is precisely describing the effect here.

 

My RF is fully focussable on the 24 2.8, the 28 2.8, 35 1.4, and 50 1.4 right now with the point of focus in focus throughout the field range.

 

I've got a really busy weekend, but I'm going to re-shoot one more time with the new chart.

 

My own ruler test, though, says the difference here is either 1) the RF adjustment--as I said, wide open this is almost (but not quite) front focussing or 2) some tolerance difference in the chrome vs black version.

 

I think it's the former Tim.

 

Here are some shots from my test (not pretty, but like I said I'll redo later today with the "Nikon" test (which is quite nice, btw--at least for close focus).

 

My three-year old was running around me while I was doing this; there may be some floor shake, even with a tripod (not kidding, and that's why I want to re-do these)

 

The focus point is the solid ruler bar before "news." IS0 1250:

 

f 1.4

[ATTACH]28027[/ATTACH]

 

f 2.8

[ATTACH]28028[/ATTACH]

 

f 4

[ATTACH]28029[/ATTACH]

 

f 5.6

[ATTACH]28030[/ATTACH]

 

F8 and f11 were also in focus at the line and before the line. But you can see the field shifting towards the back of the ruler as the lens stops down.

 

More tonight--and I'll post right from 1.4 to 11 (bigger steps in between).

 

Hi Jamie!

 

I'd guess that you need a slightly more oblique angle on the test subject - your 2.8 shot is almost oof at the point of focus an I guess it would be if it wasn't 'saved' by the fact that the depth is not extending as the ruler would were it at exact right angles to the plane of capture - impossible I know but more obliquity might show it.

 

Or of course it's not there!

 

I really look forward to the next set!

 

Thanks again

 

Tim

[egibaud]

Hi,

 

A week ago, I said I had no backfocus... as I had not noticed it clearly, due to my lack of experience with rangefinders and also because of the close portrait I had been doing. When some subject we slightly out of focus, I though it was my focussing skills that needed sharpenning :-)

 

Today I visited a friend Artemio (in this forum) and... we tested several Lenses to see how they behaved although they were uncodded and some were quite old.

 

Then we tried to compare his old 35mm Cron... and surprise! mine was out of focus in the center and very shapr in the corners, his, logically for the old model, was behaving as expected, sharp in the center soft in the corners.

 

So we pushed the testing with my Summilux 35mm and according to the distance of the subject and the aperture, the backfocus increases but is ALWAYS present.

 

My question is.... what would you do, keep it and become an expert at guessing the right focus sport or, change it for a Summcron 35mm as they do not seem to give such problem.

 

Regards,

 

Eric

[tashley]

Hi,

 

A week ago, I said I had no backfocus... as I had not noticed it clearly, due to my lack of experience with rangefinders and also because of the close portrait I had been doing. When some subject we slightly out of focus, I though it was my focussing skills that needed sharpenning :-)

 

Today I visited a friend Artemio (in this forum) and... we tested several Lenses to see how they behaved although they were uncodded and some were quite old.

 

Then we tried to compare his old 35mm Cron... and surprise! mine was out of focus in the center and very shapr in the corners, his, logically for the old model, was behaving as expected, sharp in the center soft in the corners.

 

So we pushed the testing with my Summilux 35mm and according to the distance of the subject and the aperture, the backfocus increases but is ALWAYS present.

 

My question is.... what would you do, keep it and become an expert at guessing the right focus sport or, change it for a Summcron 35mm as they do not seem to give such problem.

 

Regards,

 

Eric

 

Eric, take this with the health warning that Jamie is convinced my RF is slightly out of adjustment and I am pretty certain it isn't. All my other lenses pass my focus test, and they range from 24mm thru 90mm. The odd ones out are the 35 luxes I sent back and the 35 cron I just received. All those 35mm lenses have backfocus, though are very close at full aperture. From that point on, my chosen point of focus is OOF and the actual point of focus shifts backwards as I stop down. I have tested this very extensively on all three 35's and the behaviour is consistent. Leica told me that this is just what they do - and they warned me I would find the same with the cron, which I have.

 

Jamie and a few others have lenses that don't do this. Most people, when they look carefully, find the lux and cron DO do it. I ordered the cron because I need a 35, and if I can't get one that has perfect focus behaviour, I'd rather have a less expensive one so I am keeping it and will try to use at wide open or at f8 or 11. Between f2.8 and 5.6 I will learn the degree of focus shift required. I will also try a 35mm F2.5 CV for focus.

 

Your discovery that you have poor focus on centre and sharp corners is the same thing that initially triggered my curiosity but the reason is simple: the edges are slightly further away and therefore fall within the zone of focus.

 

I look forward to Leica introducing a 35mm designed for the M8. In the meantime, guess, bracket focus, use other lenses when possible!

 

Best

 

Tim

[egibaud]

Your discovery that you have poor focus on centre and sharp corners is the same thing that initially triggered my curiosity but the reason is simple: the edges are slightly further away and therefore fall within the zone of focus.

 

I look forward to Leica introducing a 35mm designed for the M8. In the meantime, guess, bracket focus, use other lenses when possible!

 

Best

 

Tim

 

Thanks Tim for the ... sad news :-)

 

So if I understand the solutions are:

 

1- keep the Lux35

 

2- change it for a cron35 to save money and buy an alternative lens to avoid using the 35...

 

What other people with this problem have done? would some consider a pre-asph 35mm ?

 

Eric

[carstenw]

Eric, how are your other lenses? I would at least try fiddling with the wheel adjustment before concluding that the lens is out. It is more common for the camera to be out.

[egibaud]

Eric, how are your other lenses? I would at least try fiddling with the wheel adjustment before concluding that the lens is out. It is more common for the camera to be out.

 

The problem is that my other lenses (a Cron 75 and a CV15mm) have not arrived yet.

 

So today I did the test with a friend and all his lenses focused ok, I mean taking into account the age and the lack of coding, they were from "almost acceptable" to "completely acceptable", all focused ok. The "almost acceptable" was on a Tele Elmar 90 that had this almost David Hamilton's look if you know what I mean.

 

But all of them focused perfectly on the spot, including a 35mm Cron pre-asph. They all had the normal softer corner we could expect from these lenses. My Lux35 was just the other way around soft center and sharp corner, this is how we found out about the back focus, so we could manualy correct it guessing the right spot while focusing :-(

 

So I do no think this is a rangefinder tuning problem. So if I try to fiddle with it and do obtain the right focus for the Lux35.... then it will not be ok for other lenses. By the way my Lux35 is brand new and coded.

 

Eric

[tashley]

Eric, how are your other lenses? I would at least try fiddling with the wheel adjustment before concluding that the lens is out. It is more common for the camera to be out.

 

Carsten,

 

With respect to you and Jamie this is really not RF thing. The guy from Solm's optical lab confirmed this to me. All the lenses he tested on correctly calibrated M8's do it and he said they all will. He was very confident about this. I have had three brand new 35's in the last month and they all do it, and there are a zillion (hyperbole but close!) other people out there with the same experience. Jamie and one or two others don't have the problem and it is yet to be clear why, but I cannot believe that if my 24mm, 50mm and 90mm lenses all focus correctly, that my RF can be out.

 

And don't forget that Eric was confident last week that his was fine....

 

 

Best

 

Tim

[carstenw]

Tim, I didn't mean that your M8 was out, since you have done lots of testing. It is just a check-mark that needs to be made before making conclusions.

[egibaud]

Carsten,

And don't forget that Eric was confident last week that his was fine....

 

Best

 

Tim

 

Yes Tim you are right I was positive about it until this morning. I actually reviewed pics that I took last week, and they are all ok! why??? basically because of the type of pic they were, distance from subject and also my lack of experience with range finder. I kept my favorite pics... and they are proabably the one where I focused on the nose, so the eyes were perfect... and the one where I actually focused on the eyes were deleted thinking I was not a great focuser yet!!

 

It is likely that they are more people like me that have not seen that they are not actually getting the pic focussed where they think it does.

 

By the way a big THANK YOU for all the people here who have worked on finding this out and how to detect it.... by the way.... Leica has retired the Lux 75... maybe the Lux35 is following soon.

 

Eric

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[wlaidlaw]

The new Zeiss 1.5 Sonnar seems to have lost much of it's anticipated appeal when descriptions of focusing issues of exactly the sort you describe appeared in multiple online forums. The new 85/2 Sonnar (which is was delayed around the time complaints began appearing about the 50 Sonnar) will have a progressive cam and floating elements. It will also be an order of magnitude more expensive then the 50/1.5, hopefully with the additional technology it will focus accuratley across its' aperture and distance range.

 

Zeiss' predecessor lens to the 85 ZM Sonnar the 90G Sonnar also had focussing "issues" even with film. I had mine adjusted twice and it was still a difficult lens to use. Whereas I am a great Zeiss fan and love the 35 and 21 ZM Biogons I have for my M8, I had no difficulty in going for an Elmarit-M 90 rather than waiting for the Sonnar. It may not have the ultimate MTF's that the Sonnar does but it certainly is easy to focus and use with the 1.25 magnifier (yes I have got my one Nyahh-Nyahh).

 

I do wonder if the 35mm f1.4 Summilux is a step too far in production manufacturing tolerances at the moment and regular customer examples are not always to the same standard that the press lenses are. It was well known in the trade, that a certain British car manufacturer supplied press cars, on which the engines had been very carefully blueprinted and the suspensions optimised. I am not suggesting that Leica gets up to anything as nefarious as this but it would not be unexpected, if they are sending a lens out for review, to try 5 or 6 lenses, to see which would be best to lend to the trade press.

 

Wilson

[d_brown]

I am sure there is a problem with the 35s. I have two 35mm Luxes and one 35 Cron, all new and 6-bit coded. NONE of them focus properly on ANY of my three M8s. I have 16 other lenses, some new 6-bit and some old ones I've had from the 60s. Fifteen of them focus well, interchangeably, on all three bodies. The 16th, a 50mm Lux, has a focusing problem similar to the 35s. I bought a new 35mm Zeiss Biogon. It focuses PERFECTLY!

One dealer I spoke with told me what his Leica rep told him about the 35s. I won't repeat it here. You tell me if you think the 35s don't have a problem.