Help understanding rangefinder / lens calibration

[hunta]

I've just upgraded from an M9 to an M, which I use with a Summicron 35mm v3 and a Summicron 50mm v3.

I've noticed that focusing with the 50mm is potentially slightly off. If I attempt to focus wide open on a ruler approx. 1m away it'll backfocus at around an inch off fairly consistently. Focusing at infinity seems fine. I first noticed it doing portraits at around 2.5m - the eyes aren't quite in focus (eyelashes not sharp, which is my goal) but the shirt collar for instance, slightly further back, is.

I never noticed it with my M9 and I don't notice it with my 35mm, though I haven't tested yet. The greater DOF with the shorter focal length may be masking things if the issue is with the rangefinder calibration however.

Is it possible for the issue to be with the lens?

Can anyone help me work out where the problem may be? User error is not out of the question here, and I'm aware I may be blaming new kit too hastily... On the other hand I don't have a second body lying around to test with, and I don't want to send the whole lot off to Solms for a spell at unnecessary cost if there's little wrong.

Thanks in advance.

 

[Sarcophilus Harrisii]

It's pretty hard to critically assess focus adjustment based on infinity sharpness of a 50mm lens, because even if it is wide open DOF is still going to make a slight error in focus look pretty good. But it can still be out enough to be significant at close range.

What you must bear in mind is that almost any camera which permits the photographer to optically adjust focus instead of guessing (Ie. Scale focus) has two independent or semi-independent focus systems (except, arguably, a view camera perhaps, as the ground glass used to focus is also at the film plane). A TLR has a viewing lens and taking lens which must both match. An SLR has a reflex mirror that must match the viewfinder focus to that of the film (or sensor) plane. And a rangefinder has a rangefinder focus patch that must match the focus of the lens at the film/sensor. In all cases the "passive" or guide system must be matched to the "active" system that records an image and not vice-versa.

Hence, the first point to be investigated is whether it is the lens focus (or, theoretically—but unlikely I should have thought with a new Leica—the camera body lens register) that is out: or the rangefinder system.

Without access to equipment for checking these adjustments, the simplest way to determine which sub-system is at fault is to run some comparison tests with other lenses.

If you can accurately set a close range focus point with other lenses, wide open, using the RF, it is most likely your RF is in calibration and your 50mm lens may require adjustment. On the other hand, if tests with other known good lenses consistently return deviations from the point of RF focus, it is more likely that lens register and lens adjustment is good, and that the RF itself requires calibration.

A tripod and static subject is recommended for testing to eliminate the input variables of a moving subject, motion blur and camera movement.

Given you have advised that your 50mm seemed to be performing well on another camera this does tend to suggest it is less likely to be at fault. In which case, if the RF requires some adjustment, faults with its focus should be repeatable with other lenses because it is common to all of them.

Either way the process is one of changing unknowns to knowns by substitution or elimination of variables. Ideally you would want to "jury" your tests with at least three lenses if they are not of "known good" status (or more, if you have access). Failing that, cross-referencing with another known good camera body enables direct comparisons to be made.

In the absence of either other lenses or other bodies you may need to seek assistance from a third party.
Cheers,
Brett

 

[Sarcophilus Harrisii]

Oh and welcome to Rangefinder Forum. 😉

 

[mdarnton]

You need to do very careful tests with the 35mm also. If both lenses are doing the same thing, then it's the rangefinder, probably. If not, it's a lens, probably, but you still won't know which one because you don't know which camera is right or if either is.

Rangefinders have two adjustments: first making sure that infinity is at infinity, then second, changing the amount the RF moves between infinity and close up (think of it this way---if you put one end of your two endless tape measures at infinity, the near end of both should be at the same spot, but if they're different lengths, one may end an inch before the other.)

Of course there's the possibility that both lenses and both cameras are all slightly off, but some combinations work better than others. 🙂

This is why we have that word "tolerances". Then you need a strategy. Mine would be to have the 50 spot on close up, which probably means adjusting the offending camera.

As SH observes, this is a complex problem. Solvable, but complex. So if you really care, you probably need a repairman with a complex mind to sort it out (I imagine this narrows the possibilities considerably, knowing what I do about repairmen.)

 

[hunta]

Thank you for the responses.

It has just occurred to me (belatedly) that I have live view on my M, which is independent of the rangefinder. That would at least remove one variable element from the equation, but could it discount 'camera fault' entirely?

Apologies for the questions and underlying ignorance...

 

[ferider]

Take a 2mm Allen Wrench and calibrate your M for best focus of your 50 at 0.7m min focus. Any error in focusing at further distances will be less visible because of increased DOF and less focusing accuracy.

Because of increased DOF, the 35 is less critical, and the v3 is not that sharp anyways at any distance and below f8 (well, at least mine isn't).

(I have 50 and 35 v3 Summicrons as well, and that's what I did, anyways).

In general, with used lenses, you will have a very hard time finding lenses that are all calibrated to more than an inch accuracy. On a film camera, you wouldn't even notice but the 240 is very unforgiving in that respect.

Roland.

 

[Fraser]

I've started adjusting my own M9 so I can decide which lens I use the most and at what distance. You shouldn't need to send the camera back to Germany either as any decent repairman should be able to calibrate a rangefinder.
Now that you've noticed it it will drive you crazy! thats rangefinders for you.

 

[jaapv]

Take a 2mm Allen Wrench and calibrate your M for best focus of your 50 at 0.7m min focus. Any error in focusing at further distances will be less visible because of increased DOF and less focusing accuracy.

Because of increased DOF, the 35 is less critical, and the v3 is not that sharp anyways at any distance and below f8 (well, at least mine isn't).

(I have 50 and 35 v3 Summicrons as well, and that's what I did, anyways).

In general, with used lenses, you will have a very hard time finding lenses that are all calibrated to more than an inch accuracy. On a film camera, you wouldn't even notice but the 240 is very unforgiving in that respect.

Roland.

The Allen Wrench adjustment on the roller is for infinity, not for close up...

 

[peterm1]

There have been a few posts on this topic including one where I have given a fairly lengthy description of how I measure close focus rangefinder accuracy. The shorter form description is that I take a board about a metre long and in the centre I mark an aim point using a broad marking pen. Then in one centimetre increments and decrements I mark points in front of and behind the focus point on that board. I then take the board and lay it on the floor with the camera on a tripod a measured distance from the central focus point marked on the board, to the line on the camera indicating the sensor plane. This must be exact for obvious reasons. I used 3 metres simply because all my lenses have this distance marked on them, so in addition to checking the focus by comparing the distance measured by tape measure to the distance marked on the lens itself, I can also check focus using measurement by the rangefinder for each lens at the SAME distance. This takes guesswork out of the process.

Then using several lenses in turn I focused each one first by rangefinder and then using the scale marked on the lens (set, as explained, at 3 metres as this is the measured distance to the focus point). It was then a simple matter to compare the resulting images to confirm (a) if focus was accurate or in front of or behind the focus point with each lens and by how much for each focusing method and (b) whether only some lenses were off.

If all lenses were accurate when measured by tape measure but not with rangefinder then this suggests a problem withcamera's rangefinder calibration. And it is also easy to see by how much focus is off by referring to the images to see which line corresponds to the sharpest point in each image. Of course this is an easier and quicker experiment to execute with digital instead of film (for those film shooters still out there). It also helps to mark on a piece of paper placed beside the aiming point (a) the lens used for that shot and (b) how focus was achieved for that shot (ie scale focus or rangefinder). That way you do not have to remember which shot is which.

This is the best way I have discovered to check calibration. I did not calibrate the kens myself but instead provided my camera guy with the test shots and asked him to do it. It cost me a hundred bucks or so but he had better skills and equipment than me. Also from memory the focus adjustment for close focus is different from the focus adjustment for infinity in the rangefinder system. I think it can be a bit tricky to make sure that if one is adjusted the other is not thrown out of kilter. I had doubts I knew enough to be able to get it right. Also the movements needed are so tiny that it is hard to make the adjustment without over doing it.

 

[Richard G]

My 50 Summicron served me well on film for nearly thirty years, and on the M9, until I tested it. It was back focussing by nearly 2cm at 1m! It was the same on the Monochrom. It was scarcely believable. The Leica repair agent confirmed it and adjusted it. If I hadn't tested it I might have remained happy with it. I am not so often shooting at minimum distance. An analogous consideration is the ZM C Sonnar with focus shift. Many who've never heard of focus shift will never notice it in practice. Some of us need critical focus wide open at minimum distance. For those photographers everything has to be perfect.

 

[ferider]

The Allen Wrench adjustment on the roller is for infinity, not for close up...

It moves the camera-predicted focus plane for the entire focus range.

It is of course a poor substitute for what would technically be best: a "zero tolerance calibration" of all lenses and camera, as people like Don and Sherry have done on professional kits since many years. Then again with only two lenses and the 50 being only an inch off it feels like overkill. See also http://www.dantestella.com/technical/leicadjust.html for a critical discussion of the subject.

 

[jaapv]

I've just upgraded from an M9 to an M, which I use with a Summicron 35mm v3 and a Summicron 50mm v3.

I've noticed that focusing with the 50mm is potentially slightly off. If I attempt to focus wide open on a ruler approx. 1m away it'll backfocus at around an inch off fairly consistently. Focusing at infinity seems fine. I first noticed it doing portraits at around 2.5m - the eyes aren't quite in focus (eyelashes not sharp, which is my goal) but the shirt collar for instance, slightly further back, is.

I never noticed it with my M9 and I don't notice it with my 35mm, though I haven't tested yet. The greater DOF with the shorter focal length may be masking things if the issue is with the rangefinder calibration however.

Is it possible for the issue to be with the lens?

Can anyone help me work out where the problem may be? User error is not out of the question here, and I'm aware I may be blaming new kit too hastily... On the other hand I don't have a second body lying around to test with, and I don't want to send the whole lot off to Solms for a spell at unnecessary cost if there's little wrong.

Thanks in advance.

It is more than likely that the lens is off. First have a reputed technician check your lens.

 

[jaapv]

It moves the camera-predicted focus plane for the entire focus range.

It is of course a poor substitute for what would technically be best: a "zero tolerance calibration" of all lenses and camera, as people like Don and Sherry have done on professional kits since many years. Then again with only two lenses and the 50 being only an inch off it feels like overkill. See also http://www.dantestella.com/technical/leicadjust.html for a critical discussion of the subject.

No. The close-focus adjustment is the screw that is on the other side of the lever. The system is non-linear.
If you start doing this without knowing what you are doing, you throw the whole system out.