When ∞ is not infinity

[rjsphd]

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I just plugged my M 75mm Summilux into my recently bought (used) SL via the Leica adapter and have discovered that objects at a long distance are not in focus at ∞. but at a setting slightly shorter than ∞.  The lens has not been used since it was CLA'd by Leica.  What are the possible source of this situation?  

Thanks in advance for sharing your wisdom.

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[grahamhoey]

Check out the various comments in the forum topic "Third party lens performance on SL". My understanding is that is nothing to do with the lens but it is the adapter. I had the same issue using the Leica adapter and some have made small changes to the adapter to fix the issue. I also just got the Novoflex adapter and my M lenses focus perfectly to infinity on that. No guarantee of that however, think I may have just got lucky.

[mmradman]

If you ar3 going to use th3 lens on SL only don’t worry too much about it, use EVF to provide you accurate focus and ignor3 lens focusin* scale.

Now, if you also plan to use it on M camera and focus with RF than there may be problems, it may be worthwhile checking, do you have access to M camera with live view.? Unforunetly having lens serviced by Leica or any other is not guarantee that it was done correctly, some users reported multiple service trips.   

[bags27]

This is very common today, and there are lots of reasons given. See for example,

https://www.bhphotovideo.com/explora/photography/features/who-killed-infinity-focus%3F?BI=572/?BI=572&kw=&gclid=CjwKCAiAo8jgBRAVEiwAJUXKqBNlqE35B_vLI1PucYMzM-wb5JtMBNJPEdQdXGaXqmqqFTmgiw4X-BoCGDMQAvD_BwE

The one I've always believed is that it has to do with the IR spectrum. Leica, in the link above, suggests thermal heating, which is, I believe, the 2nd most frequently offered explanation.

FWIW, my Q does the same thing. Doesn't really affect my photos when I'm in manual mode.

[mmradman]

1 minute ago, grahamhoey said:

Check out the various comments in the forum topic "Third party lens performance on SL". My understanding is that is nothing to do with the lens but it is the adapter. I had the same issue using the Leica adapter and some have made small changes to the adapter to fix the issue. I also just got the Novoflex adapter and my M lenses focus perfectly to infinity on that. No guarantee of that however, think I may have just got lucky.

OP stated he is using Leica adapter, to best of my knowledge no issues with that one.  I exclusively us3 M and R lenses with Leica adaptors, for R I stack two adapters. Absolutely no focusing issues.

[John McMaster]

I think he is meaning the 70mm Summarit-S lens rather than the M 75mm......

john

[BernardC]

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The main reason is thermal expansion, along with the fact that the adapter is a metal tube that isn't factored into the original mechanical design for the lens. A second reason is mechanical tolerances, and the fact that's better to have an adapter that is slightly too short (focuses past infinity), rather than one that is too long (doesn't focus to infinity).

As the B&H article (quoted above) mentions, traditional mechanical (non-AF) lenses can be designed in a way that thermal expansion is self-compensating. You can't do that with an affordable adapter, so manufacturers make them a few microns short. That means that they will focus slightly past infinity at room temperature, but they still focus to infinity when heated-up to 40 degrees or more in the hot sun.

Many long lenses focus past infinity (by design) for the same reason.

Your best bet is to fine-focus by eye, which is easy to do with the SL. The alternative is to have your camera and lens collimated at your shooting temperature. That's done with cinema cameras on high-budget productions, but it's a bit too much bother for most stills photographers.

[thighslapper]

I've heard the 'thermal expansion' business before ... but if you actually do the calculations using the thermal coefficients and the thickness of the SL-M adapter the differences are miniscule over the expected temperature variations.

I'm sure it's more to do with the mechanical tolerances and in particular Leica tolerances in lens calibration.

The SL-M adapter is approx 0.1mm off in terms of being precisely adjusted for a perfectly adjusted M lens at infinity. That's a lot of leeway and far more than is required for thermal issues. 

I've posted plenty of times about all this going back to when the original adapter was released for the T. 0.08 -0.09mm shims in the adapter completely correct the error .... assuming your lenses are perfectly calibrated to start with ...... which is opening another can of worms ....

Edited December 13, 2018 by thighslapper

[rjsphd]

14 hours ago, thighslapper said:

I've heard the 'thermal expansion' business before ... but if you actually do the calculations using the thermal coefficients and the thickness of the SL-M adapter the differences are miniscule over the expected temperature variations.

I'm sure it's more to do with the mechanical tolerances and in particular Leica tolerances in lens calibration.

The SL-M adapter is approx 0.1mm off in terms of being precisely adjusted for a perfectly adjusted M lens at infinity. That's a lot of leeway and far more than is required for thermal issues. 

I've posted plenty of times about all this going back to when the original adapter was released for the T. 0.08 -0.09mm shims in the adapter completely correct the error .... assuming your lenses are perfectly calibrated to start with ...... which is opening another can of worms ....

Does this mean that without them my distance shots will be out of focus when my M lenses are set to ∞? And where on earth do I obtain 0.09mm shims?  

[thighslapper]

Infinity will always be before the infinity end stop on a manual Leica M lens. 

So ...... you cannot set the lens to infinity and expect the image to be in focus all of the time when you take far distant shots. 

Depending on the lens and the aperture you may get away with it most, some or none of the time ..... of course dependent on the DOF at the particular settings. 

So ..... with manual  lenses ..... particularly >35mm and smaller apertures you cannot be lazy and will have to check focus on the LCD or EVF for far distance shots.  

That's not a problem 99% of the time ...... just a minor nuisance if you want to take a quick distance photo and just want to set the lens and go as you would with a M rangefinder. 

Nothing is commercially available to alter the length of the Leica SL-M adapter .... but you can dismantle it and add material cut to shape around the perimeter where the two halves meet. LCD protection film is about the right thickness and has the advantage that it is tacky so stays in place while you reassemble.

If you do this ...... check all the lenses you intend to use to ensure you have not converted a surmountable problem to an insurmountable one where you can't reach infinity focus as you have  effectively made the adapter too thick. 

To be honest, as long as you are aware of this limitation and don't get caught out there is no problem, and correcting it is only for grumpy people like me who get irritated when allegedly precision instruments don't work perfectly. 

Edited December 14, 2018 by thighslapper

[helged]

20 hours ago, rjsphd said:

Does this mean that without them my distance shots will be out of focus when my M lenses are set to ∞? And where on earth do I obtain 0.09mm shims?  

Sorry for not getting this, but with the SL, you can focus by focus magnification. Take the lens out, on tripod, under clear sky, and you can exactly determine where the infinity is. Either remember this, or mark the lens with a piece of tape etc. When testing various lenses this way, you will likely find that subject far away needs to be focussed. If you have one lens, you can adjust the thickness of the adapter to get the infinity mark at infinity focus. If you use the same adapter for two or more lenses, what's working for one lens may not work for the others. So I would skip the adapter modification. And if you alter the thickness of the adapter, ensure that the modified thickness is constant throughout the adapter ring. 

Another, related issue is the flatness of the lens. Most wa lenses do not focus on a flat plane in front of (and perpendicular to) the lens. Therefore, at least when shooting wide open, you will typically have the center of the image in focus and a somewhat defocussed image off the center. 

The above is described in some detail in the thread 

 

Edited December 15, 2018 by helged

[rjsphd]

Thanks to all who wrote in.  Very helpful.  I don't think I will be shimming my adapter anytime soon.  Instead I will use the viewfinder and not instinctively turn all the way to the ∞ mark.

 

One last question:  if my M lenses (wide open) on my Leica adapter focuses for infinity at the mark on the lens barrel  2mm before the  ∞ mark, then what, if anything, is in focus when I turn all the way to the ∞ mark?

[scott kirkpatrick]

Nothing will be perfectly in focus.  But if you want to use scale focus accurately for closer objects, offset those settings by 2 mm as well. 

[lanetomlane]

Temperature and thermal expansion is a greater problem with very long telephoto lenses. That's why most wildlife photographers use white lenses in hot countries, as they don't absorb the heat as much as black ones.