Back Focus Problem

[Perspectics]

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That is YOU adjust the wheel that the lens cam hit to make sure that at the infinity stop on the lens the images line up in the view/rangefinder at something that is really at infinity, like a star or the moon (A star is better). Trying to do this withanything else, like a pole or building that YOU THINK is far enough to be at infinty can give you false results.

 

You use a 2mm allen key to turn the wheel mounting point which is off center of the wheel (or is it the wheel is off center to the center of that adjustment point?) to make the adjustment.

 

There are a few threads on this subject and a simple search will turn them up.

 

Ups - interesting! I was totally mistaken as I assumed Catatac was somehow able to fix the *picture* by some mysterious focal-point-shifting software called alen key

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[Shootist]

Ups - interesting! I was totally mistaken as I assumed Catatac was somehow able to fix the *picture* by some mysterious focal-point-shifting software called alen key

well it is just the sign of the times. We all have our heads filed with 1's & 0's or so it seems at times.

Easy mistake to make. There is nothing that can fix a out of focus shot.

[Catatac]

Ok, but what was the ISO settings that time?. higher then 640? it is an inside shot right?

 

 

Theo

 

Quite valid questions however the ISO was 160 and it was an external shot. The Lux really did have back focus problems. However, it highlighted the focusing difficulties I had with the Lux due to circumstances such as movement and interior shots.

[Albert4321]

Focus shift is a property of lens design. Backfocus is a characteristic of an image, and may be related to focus shift, to rangefinder inaccuracy, or to photographer error.

HC

 

I understand the focus shift is a property of lens design. And I also get confused (sorry I am new to RF) when someone posted that their copy of 35lux or 50lux has no focus shift, and suggested other to send their lens back to Leica to adjust it. Are they blowing smoke, or they are compensating, or indeed it is adjustable due to poor QC from Leica where the lenses shipped out of tolerance?

[ho_co]

Albert--

Has nothing to do with "new to rangefinder." Leica produces some of the most demanding designs on the civilian market. You're not likely to get into such discussions with other manufacturers simply because they're not doing anything like that.

 

Blowing smoke? Depends.

 

Three examples concerning the 35/1.4 ASPH:

 

ONE--LFI says this lens exhibits some backfocus problems because it lacks a floating element. The magazine implies that if designed today, it would have a floating element.

 

TWO--In a thread started by Tim Ashley (whose work is recommend on Leica's M8 site), two posters said their own samples of the lens didn't exhibit the problem. When they both undertook some tests to verify that their assessment was correct, one found no backfocus and the other found a little that he had been unaware of.

 

THREE--Tim Ashley started that thread because Leica Solms told him something to the effect that, "Yes, you're right. Your lens has what you call a 'problem' because the lens is designed that way." It took Tim several months and a personal visit to Solms to demonstrate to them that the lens was not properly adjusted. They fixed it at no charge. And they discovered that the test techniques that had previously been adequate for lens testing were inadequate for the M8.

 

In other words, Leica has learned that the design of the M8 requires that they modify some of their QC procedures.

 

The LFI article said that some lenses had got through final inspection that didn't meet their quality standards. But (my opinion) some lenses were likely shipped that did meet the standards in effect when they were produced but are not within the demands of the M8.

 

It all goes back to producing highly complex designs that require very tight standards to produce properly, and then building a new camera so demanding as to show that even those tolerances are no longer enough.

 

There are certainly variations from lens to lens in every manufacturer's line; I think there is likely less sample variation from Leica lenses than is the case with others. But since the Leica lenses are so highly corrected, the deviations may be more noticeable. (Not sure I'll want to stick with that argument long-term , but what I'm saying is that if one lens is edge-to-edge sharp and the next sample isn't quite so sharp in the corners, the difference may be more noticeable than if both were only so-so at the edges.)

 

Has Leica's QC slipped? Maybe; I don't know. But they are definitely aware of the problems customers are having; Steven K Lee has commented on it publicly. If their QC did slip, they are now paying the price in warranty repairs. That means increased attention to the difficulties in future; and that in turn means increased costs.

 

Maddening spiral, but if anyone can find and fix the problem, I think Leica can.

 

I hope that's not too philosophical or too sanguine, but it's my response to your question.

 

--HC

[mweiner]

Howard, I enjoyed your "philosophical" summary of the 35 1.4 asph backfocus issues.

Perhaps you or others can give me some advice

about a practical question which puzzles me despite my reading of

Tim Ashley's thread and Sean Reid's 35mm lens review:

 

I have a 9 month old passport covered 35mm 1.4 Asph.

It focus shifts about 6-10 inches.

Consistently on both my M8 bodies (one of which

was returned from Solms today) and both of which

focus accurately with my other 6 lenses. I obtain

the following results at 4, 6 and 10 feet using a tripod

and both Sean's 3 bottle test or the Nikon 45 degree focus chart:

 

At f1.4 the middle bottle (or 'this line should be in perfect focus")

is indeed in perfect focus. As expected, the front bottle and the rear bottle

are not in focus.

At f2.8 (stopping down without changing anything else and

without refocusing), the middle bottle is not in focus;

the bottle behind it (the third bottle and a fourth bottle) are

in focus. With the Nikon chart, the focus point is no longer in focus

and the field of focus starts about 4 inches to the rear.

 

BTW: Under the same test conditions, my son's

chrome 35mm 1.4 asph, recently dropped 5 feet onto the

Great Wall of China, shows perfect focus at 1.4 and some shifting of

focus at f2.8, but the middle bottle is still in acceptable focus.

 

All of those results are consistent with the general conclusions

that some samples of the 35 1.4 asph show back-focus and

other's don't. However, those general conclusions don't

resolve my specific practical question.

 

My question is:

If I return my back-shifting 35mm 1.4 asph to Solms,

will they be able to adjust it so it performs similarly

to my son's chrome 35mm 1.4 asph? That is, can they adjust it

so that the middle bottle will remain in focus not only

at f1.4 but at f2.8?

[Shootist]

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My question is:

If I return my back-shifting 35mm 1.4 asph to Solms,

will they be able to adjust it so it performs similarly

to my son's chrome 35mm 1.4 asph? That is, can they adjust it

so that the middle bottle will remain in focus not only

at f1.4 but at f2.8?

I think Howard just answered that with the help of Tim Ashley's work and frustration in getting his 35/1.4 to focus correctly.

If Leica has any kind of memory they should now be able to adjust the 35/1.4 correctly so that it does not focus shift as much and always stay within the DOF range of any given f/stop.

The only way to tell is to send it in with a detailed letter of the problem.

[ho_co]

Michael--

They can improve it; I don't know if they can get it to "perfect." I agree with Ed: Send it in and let them look at it. It's unusable for you now, right? They won't make it worse.

 

As you describe it, the center of the lens field focuses correctly with the rangefinder, and then as you stop it down the focus plane shifts out of the lens's depth of field.

 

Leica can definitely make it better. They may need to set it up so that it front-focuses a bit at full aperture. That would mean that the same focus shift it currently exhibits would not shift the focus plane outside the lens's depth of field at any aperture.

 

The one thing I dislike about Leica's service in the US is that there is such poor two-way communication. My experience has been that in a case like yours, you will send the lens in with problem description. They will generate a work order, adjust the lens, and return it. You will probably not be offered the chance to be told whether the lens is being repaired in a way that lets it focus accurately wide open and keeps focus within DoF as it's stopped down, or whether it is being adjusted to best compromise, front-focusing a bit wide open in order to compensate for the focus shift.

 

All lenses are a compromise, of course. Why yours and your son's don't behave the same way I don't understand. Maybe somewhere along the way, some kind of shortcut was implemented, but there's no way we can be sure of that.

 

If you're in the US, try to reach Robert Fisk. He is straightforward and helpful, and if anyone can get you details, he can. But if the lens needs to go to Solms, his communication route may be short-circuited.

 

If you're sending the lens directly to Solms, Tim Ashley's experience indicates that there is better communication through Customer Service than in the US. But his experience also indicates that even that communication may still not be as good as we would want.

 

I understand very little of how Leica's lens designs work, but my guess is that the focus shift your lens has is there to stay. After adjustment, the lens will probably not be quite as sharp on the middle bottle wide open but will not shift as badly out of focus as you stop it down. In other words, I don't think there's anything Leica can do with the lens cell itself. They can only readjust its position within the mount.

 

If you can get more information on what they can do, please let us know. The 35/1.4 is respected as one of the best designs ever. That holds for film, but slight sample deviations are much more noticeable on the M8.

 

Nothing definite here, Michael, except that I'd let Leica look at it and try to get a better explanation from them of what's wrong and what can be done; and of whether the adjustment will be a correction of the error, or just an improved level of compromise.

 

Good luck!

 

--HC

 

PS--Just so I don't paint too rosy a picture, see also http://www.l-camera-forum.com/leica-forum/leica-m8-forum/42390-backfocusing-75mm-lux.html. That thread says that Solms' first attempts aren't always successful. But the thread concerns the 75/1.4, discontinued partially because of its backfocusing issues on the M8. In other words, it's an older design than your 35/1.4, and shows its age more. I would judge that Leica discontinued it because they are less confident of being able to adjust it to the needs of the M8 than is the case with the 35 Summilux.

 

PPS--OOPS! I see you're already reading that thread.

[Jamie Roberts]

{snipped}My question is:

If I return my back-shifting 35mm 1.4 asph to Solms,

will they be able to adjust it so it performs similarly

to my son's chrome 35mm 1.4 asph? That is, can they adjust it

so that the middle bottle will remain in focus not only

at f1.4 but at f2.8?

 

Correct focus performance means having both the M8 rangefinder *and* the lens in spec and in tolerance (adjustment).

 

When I first got my M8, the infinity focus on the rangefinder was off. Plain and simple: my 35 and 50 Lux ASPH both backfocused badly, though were just acceptible wide open. Since the current 50 Lux shouldn't exhibit that problem, I suspected the rangefinder itself was off.

 

When I fixed the rf infinity focus (that's the allen key fix) both of them kept the point of focus IN FOCUS throughout their aperture range, though the field does indeed shift when stopping down. That's ok; wide open you're just happy to get the focal point sharp anyway, IMO.

 

This is no worse than any other fast lens I've used on any other system, Leica or otherwise. Superfast lenses have compromises built into them.

 

Tim Ashley (where is Tim these days anyway?) had defective equipment, including one defective M8 and--if I recall correctly--a mis-aligned 35 lens as well.

 

Remember, his 35 luxes were off *by several feet* at distance at f4--something patently ridiculous for any modern lens, let alone a Leica lens, let alone the 35 Lux, which is extremely sharp under those conditions, even on the M8 and even with driver error!

 

I personally had a backfocusing 75 Lux. It was backfocusing by about 5 cm and that got worse with the focus shift from 1.4 through to f 3.2 and then vanished by f4, where DOF usually took care of it.

 

Since the 35, 50 and 90 'cron didn't exhibit this behaviour, I realized that the lens itself was the problem. Sure enough, when Kindermann Canada (Gerry Smith) had a look at the lens, without the M8, he said "it can't acheive infinity and needs an adjustment).

 

So the moral of the story is check your M8 with something long-ish and reliable like a 90 'cron and 50 Lux ASPH. If those lenses work, then the reason your others don't is a lens problem; if they don't work, then your M8 needs work as well.

 

BTW--the only exception I know to the "DOF will cover the focus shift as you stop down" story is the Noctilux, which needs some compensation around f2 as you stop down. But since I shoot that from f1 - 2 mostly, I don't find that to be a problem at all.

[ho_co]

... Tim Ashley (where is Tim these days anyway?) had defective equipment, including one defective M8 and--if I recall correctly--a mis-aligned 35 lens as well.

 

Remember, his 35 luxes were off *by several feet* at distance at f4--something patently ridiculous for any modern lens, let alone a Leica lens, let alone the 35 Lux, which is extremely sharp under those conditions, even on the M8 and even with driver error! ...

You're right, Jamie. Solms was slow to discover that Tim's 35/1.4 was simply 'way off.

 

He would focus on an object at, say, 15 feet; and the object in the center of the frame would be completely out of focus. Objects 10 feet behind it would be sharp--but the strange thing was that objects 15 feet away (i.e. in the intended focus plane) but on the edges of the frame would be sharp.

 

Others on the forum visited Leica dealers and found that a number of samples they had in stock of the same lens exhibited the same behavior.

 

We sort of had the feeling on the forum that it was Tim's persistence and the diligence showed by others in demonstrating that the problem was wider-spread than anyone could have imagined which brought Leica to the recognition that the old lens test procedures were inadequate to the needs of the M8.

 

And Jamie, as I recall, you did a great job of keeping us rational on that thread.

 

I've wondered as well where Tim is. Leica's web site still has a link to his Venice pictures. I guess since he got the technical problems straightened out, he must be out taking pictures. Strange thought, isn't it?

 

--HC

[mweiner]

Thanks to all for the advice about my back focusing 35mm 1.4 A.

 

As per Jamie (from whom I have learned a ton),

I am sure the body is not the problem because:

(1) I have seen the same

problem behavior on 3 bodies,

(2) on the body I am mainly using

for testing (back from a Solms adjustment 2 days ago)

my other 6 lenses including a 90mm f2 and 75 1.4 focus

accurately, and

(3), the 35 itself focuses accurately wide open on that body.

 

Putting together Ed's and Howards suggestions here,

I will email Mr. Fisk with images of my bottles

taken with the 35mm at f1.4, f2.8, and f4.

I will seek his advise about whether sending the lens

to New Jersey or to Solms (which I'm willing to do)

will be more conducive to a solution.

 

I think that a new 35mm 1.4 A should perform as well at keeping

the point of focus in focus at all apertures as most other copies

(my son's and the one Leica supplied Sean Reid to test in his review of 35mm lenses) so I will ask for my lens to be brought to those

specifications or replaced.

 

Some people here may recall that Guy Mancuso sold his

35mm 1.4 A and bought a used 35mm f2 IV because he

didn't want to deal with the "hassle". I have a very nice

35mm f2 IV (as well as a perfect 75mm 1.4),

but naturally I want it all. That is, I want my 35 1.4 to work

as well as many other copies of that lens.

 

I guess I am in for the hassle, and will report back to this thread

as it evolves.

[thpeters]

ISO has nothing to do with focus. Whether the shot was taken at ISO 160 or 2500 does not matter. Back or front focus is camera/lens dependent and ISO will have no affect on focusing.

What would make you think any differently.

 

I know, thatISO has nothing to do with focus, but the shot looks to me like a very low shutter time, and I forgot to write down with a higher ISO, the shutter time get higher too, result less camera shake problems.

 

To me it looks still head movements, I have the same with my summilux 50 mm, shutter time 1/30 give the same results, with taken pictures from people, and a non movement subject is sharp.

 

Theo

[Shootist]

I know, thatISO has nothing to do with focus, but the shot looks to me like a very low shutter time, and I forgot to write down with a higher ISO, the shutter time get higher too, result less camera shake problems.

 

To me it looks still head movements, I have the same with my summilux 50 mm, shutter time 1/30 give the same results, with taken pictures from people, and a non movement subject is sharp.

 

Theo

OK Theo I now understand why you asked about ISO but to me the image we are talking about does not show any camera (Man behind the camera) movement or subject movement. You can count the hairs on the back of the subjects head/neck on the left side, even in the low quality JPG posted here (and I'm looking at the image on a 10+ year old CRT monitor because I'm at work). Clearly you wouldn't be able to do that with low shutter speed and camera/user shake. Also the shirt at the shoulder would be blurred, it is not, at least from where I'm sitting.

[ho_co]

... I will email Mr. Fisk with images of my bottles

taken with the 35mm at f1.4, f2.8, and f4....

Not recommended. He hasn't time to look at someone's test shots and respond. Leica has their own test methods.

 

... I will seek his advise about whether sending the lens

to New Jersey or to Solms (which I'm willing to do)

will be more conducive to a solution....

If you want to avoid Allendale and send directly to Solms, just do so. Don't waste their time asking their opinion.

 

Just send the lens to NJ. They will decide whether they can do the job or whether the lens should go to Solms. It's not faster to let them send to Solms, but it's a heck of a lot less hassle. NJ knows what's in their field of expertise and what's not.

 

... I think that a new 35mm 1.4 A should perform as well at keeping

the point of focus in focus at all apertures as most other copies....

Why "most" other copies? I think they should all do so.

 

... I will ask for my lens to be brought to those

specifications or replaced....

Ask what you will, but my suggestion is not to get too puffy with Leica. Doing so implies that you think they are incompetent. You don't want the man repairing your lens to think you don't trust him.

 

... I guess I am in for the hassle....

Michael, you may be getting a little off base. You should be in to get the lens brought up to specification. When you start letting ego intrude, you're missing what Leica is there for.

 

 

BTW--Why are your posts all broken into such short lines? (I'm just curious and hope the question poses no offense.)

 

--HC

[mweiner]

Howard, you are more that right on several points. I have decided not to send the backfocusing 35 1.4 A to Leica. The story leading to that decision, clarifies at least for me, many of the aspects of the forum's discussion of that lens's BF problem that had confused me.

 

As my first step to characterize the problem to present to Leica, I tried to exactly duplicate Sean Reid's method of focus testing as described in his article/review of 35mm lenses. He tested at three feet so that is what I did. Low and behold, my results with my lens were almost identical to his with his copy of the 35 lux!

 

However, I still felt that my lens was not performing as well as it should. In general, I think testing at 3 feet too much more forgiving than tests at longer distances. Sean raises this possibility in his discussion of his test results and said that he repeated his tests on the lens at 18 feet and found nothing that would concern most photographers under most circumstances. That is likely true -- at 18 feet. In my unskilled approach to photography, I like to use the lens at 4-7 feet with maximal sharpness of the target -- and that is where the lens was failing to meet my expectations. Guy Mancuso, who BTW decided to give up his 35 1.4A because of it's issues, has written that for his type of photography he prefers to test all his lenses at 10 feet. At any rate, I also repeated the tests at 10 feet. At that distance, the issues that concerned me were apparent: At f 1.4 the target of focus was at the rear end of the field of focus; at f2.8 and f4 the target was no longer in focus and the field of focus began about 5 inches beyond the target. I had the same results at 4.5 feet where it really matters to me.

 

I have up to now avoided defining how I evaluate what is "accurate" or "acceptable focus" and as I progressed from ignorance to semi-enlightenment, I began to understand a possible reason why some folks are disgusted with their copies of this lens while others are happy, to see how it might come about that folks may get their lenses back from Solms unchanged as "being within spec's", and how Guy could decide to give up on the lens while Sean evaluated it as satisfactory. (I'm not including here situations such as Tim Ashley's egregious problem.)

 

As I was doing the tests, I was saving the *.dng files to process to 100% crops to show Leica my problem. However, it dawned on me (duh) that at 100% crops of my 10 foot results for f2.8 and f4, the target of focus would likely be within the depth of field. I realized that my evaluations and determination of the depth of field were based on pixel peeping at the M8 lcd maximum zoom, and that in fact at the next click of the wheel to reduce the zoom, I could not see the problem. Certainly I didn't have grounds to get into a pissing war with Leica about my 35 lux A.

 

However, this is not the end of the story for me. My six other lenses including my old 35mm summicron IV (also at 10 feet) do stand up to the extreme criteria I was using, and I want to expect the same performance from this technically advanced and raved about modern 35 lux. A possible solution has already been suggested by others in this thread and elsewhere which is clearly the way to go based on my test results: Adjusting the lens so that at f1.4 the focus target is at the front end of the field of focus will likely bring the point of focus at f2.8 and f4 within the field. Months ago, thinking I had a defective, 'bad copy' of the lens, I blew off Don's (DAG) suggestion to that effect, but now I may send the lens to him for that adjustment. He and I will need to consider the conditions (distance and zoom) for determining the DOF so that I'll not be unhappy that the focus point at 1.4 is too far forward (front focused) of what I consider the field.

 

However, there is one more consideration for this discussion. Like others, I have learned to compensate at the apertures above f1.4. The compensation is actually very simple and for my purposes works consistently. I have determined the degree to which the rangefinder images just don't quite overlap which is eqivalent to focusing on a point 6 or 7 inches in front of what I really want in focus. Once I learned what that looked like in the viewfinder focus patch, I wasn't in the situation of trying to focus on the empty air 6 inches in front of a subjects face. I think of this compensation as 'dragging the field of focus forward over the point of focus and it works quite well for me at the distances 3.5-10 feet where I care. Therefore I'm wobbling about the pros and cons of sending the lens for adjustment.

 

I've detailed this long tale in hopes it may be pull together much of the wisdom of the forum regarding this much praised and maligned lens.

 

ho_co wrote:

BTW--Why are your posts all broken into such short lines? (I'm just curious and hope the question poses no offense.)

 

It's probably not wise to add to this already long post and what follows won't be of interest to most people, but your polite question deserves an answer. Like many old folks, I moved from an old typewriter with a carrige return to typing at a computer terminal. In the earliest days of unix, the text editors were 'line oriented' -- specifically the primtive ed and ex of days gone by. When the newer, now venerable and passe, "screen oriented" editors vi and emacs became available, I was working on a remote terminal over a 300 baud error _un_-corrected line so that every piece of static would rearrange my screen and jump the cursor to some random location. At any rate, I stayed with old ex which worked so well for me and didn't shake the habit of hitting <enter> at the end of every line. I have been trying to just keep typing past the right border as you all do, but I still often hit <enter> when I get to the border. This makes things look even uglier than my trying to keep the lines even and short enough not to be munged by the native html formatting.

 

Michael (The Old Man from the days of the Underwood)

[ho_co]

Michael--You're one helluva Dude!

 

Not only did you use Underwoods, but you also speak Unix! There aren't many like you, my friend!

 

I understand your choice in regard to the 35 Summilux; you've explained it very well. The LFI article discussing the reasons for backfocus suggested that it was easy to learn to compensate for a lens's characteristics, just as you've done. As you can imagine, that drew a slew of "What do you mean I have to compensate for the behavior of a lens that costs this much" responses on the forum.

 

It seems to me that you've got the tinkerer spirit, which is marvelous these days when people want an instant fix and suggest willy-nilly to "return it and demand replacement," instead of trying to discover what the specific problem is so that Don G or Leica or whoever can fix it to their needs.

 

There are many things we don't understand about how these things go together, but I think you're well on your way to understanding them better than most of us. Sounds to me as if you're very close to getting it into top shape!

 

Bravo!

 

--HC

[JHAG]

See attached chart. This is close to perfect focus...leading figure 8 and trailing figure 8 are both inside DOF. Backfocus would show the trailing figure 8s sharp and the leading one out of the DOF. Backfocus can be caused by either the camera or the lens. Many of the ASPH lenses also exhibit "focus shift" which is gradual backfocus as you stop down. The reason this is such an issue ..is that the apparent DOF using the M8 is much tighter than with prior film Ms. Basically you can just see it more clearly.

 

Glen,

Where did you find this chart ?

I've looked here and there with no avail…

[glenerrolrd]

Glen,

Where did you find this chart ?

I've looked here and there with no avail…

Sorry that chart is on the wall at Leica NJ. I have tried to get one but so far no luck. Most used chart is the D70 Focus Chart which is readily available by Googling.

[Advertisement]

Hallo,

Look here: Leica M

[JHAG]

Sorry that chart is on the wall at Leica NJ. I have tried to get one but so far no luck. Most used chart is the D70 Focus Chart which is readily available by Googling.

 

I see : how much is the wall of Leica NJ ?

P.S. : I already tested the D70's chart. Puzzling results : at 5,6, the "Focus here" words are the most focussed of all, but not that focussed though.

[Shootist]

Sorry that chart is on the wall at Leica NJ. I have tried to get one but so far no luck. Most used chart is the D70 Focus Chart which is readily available by Googling.

 

Try this chart. It resembles the Leica chart. It is meant to be printed on 13" x 19" paper.Leica Focus chart 2.pdf