What's acceptable "focus tolerance" for the rangefinder system?

[shawn2nd]

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Hey Guys, 

I'm curious, with the rangefinder system, how much focus tolerance can be expected when both Camera and Lens are properly calibrated? To give a use case, the other day I was out with my M6 + Modern Summart 35mm f.25 and I was shooting the corner of a distant building that had a clear blue sky as its background. I threw the focus tab all the way to its hard stop at infinity, took the shot, and at closer investigation noticed that the corner of the building actually wasn't in perfect focus. I had to bring the focus tab just a hair back to the left to get it in focus in the RF viewfinder. Whether or not the end result is in focus, not sure yet as this roll is still in the camera 🙂

The M6 was just CLA'd in February at Kamera Express in The Netherlands, and the Summarit was purchased used from Leica Store Munich. In practice, this doesn't bug me that much as I rarely focus to infinity with the type of photography I do, buuuuut on the flip side of that, the CLA and Lens are still under warranty, so if I were to get something checked, I'd prefer to do it now while I still don't have to pay out of pocket. 

I would just hate to be without the M6 and Lens again for potentially weeks + months only to discover that "one and/or both are within acceptable tolerances." Haha, so what do you guys think? 

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[TomB_tx]

29 minutes ago, shawn2nd said:

a distant building

How far away was the building - it may not have been "infinity" by Leica definition, but still could be an RF issue.

Very likely not the Summarit - not much to be off on them. I have had my M6 come back from a CLA with the RF mis-adjusted and claimed to be "in factory spec" when returned to check with that tech. Sent it to DAG instead and he calibrated it correctly

[shawn2nd]

38 minutes ago, TomB_tx said:

How far away was the building - it may not have been "infinity" by Leica definition, but still could be an RF issue.

Very likely not the Summarit - not much to be off on them. I have had my M6 come back from a CLA with the RF mis-adjusted and claimed to be "in factory spec" when returned to check with that tech. Sent it to DAG instead and he calibrated it correctly

I'd say it was def infinity, had to be a good 100m away at least haha

[jaapv]

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To add, my personal tolerance is zero. 

[lct]

55 minutes ago, shawn2nd said:

[...] it was def infinity, had to be a good 100m away at least [...]

Was the corner at the same distance as the focus point?

[spydrxx]

Infinity has several meanings. One is that optical infinity is approximately 1000xfocal length of the lens. A second is that that infinity should be an object about or at least 1000 meters away. All that aside, some lenses are designed or calibrated to not focus on infinity wide open but at approx. f/4 - to my surprise I had a note from DAG on one of those he was working on for me, where because of focus shift he adjusted infinity focus to take place at f/4 rather than wide open. Lastly, the "infinity lock" doesn't mean the lens is focused on infinity, it is merely a point on that end of the focusing scale for locking the lens movement in place for proper attachment and detachment, so to not throw the calibration out of whack by twisting something too hard. Some lenses have exact focus in the center of the frame but focus decreases as you move towards the perimeter. If you were shooting wide open and the building corner was centered in the frame, I wouldn't worry about it, but it might mean you merely need a slight tweak on either the RF mechanism or the lens.. 

[jaapv]

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2 hours ago, shawn2nd said:

Hey Guys, 

I'm curious, with the rangefinder system, how much focus tolerance can be expected when both Camera and Lens are properly calibrated? To give a use case, the other day I was out with my M6 + Modern Summart 35mm f.25 and I was shooting the corner of a distant building that had a clear blue sky as its background. I threw the focus tab all the way to its hard stop at infinity, took the shot, and at closer investigation noticed that the corner of the building actually wasn't in perfect focus. I had to bring the focus tab just a hair back to the left to get it in focus in the RF viewfinder. Whether or not the end result is in focus, not sure yet as this roll is still in the camera 🙂

The M6 was just CLA'd in February at Kamera Express in The Netherlands, and the Summarit was purchased used from Leica Store Munich. In practice, this doesn't bug me that much as I rarely focus to infinity with the type of photography I do, buuuuut on the flip side of that, the CLA and Lens are still under warranty, so if I were to get something checked, I'd prefer to do it now while I still don't have to pay out of pocket. 

I would just hate to be without the M6 and Lens again for potentially weeks + months only to discover that "one and/or both are within acceptable tolerances." Haha, so what do you guys think? 

I'm a bit surprised that you used Kamera Express as a CLA option - it is a large international camera retail chain which farms out repairs to - ????

[dpitt]

3 hours ago, shawn2nd said:

Hey Guys, 

I'm curious, with the rangefinder system, how much focus tolerance can be expected when both Camera and Lens are properly calibrated? To give a use case, the other day I was out with my M6 + Modern Summart 35mm f.25 and I was shooting the corner of a distant building that had a clear blue sky as its background. I threw the focus tab all the way to its hard stop at infinity, took the shot, and at closer investigation noticed that the corner of the building actually wasn't in perfect focus. I had to bring the focus tab just a hair back to the left to get it in focus in the RF viewfinder. Whether or not the end result is in focus, not sure yet as this roll is still in the camera 🙂

The M6 was just CLA'd in February at Kamera Express in The Netherlands, and the Summarit was purchased used from Leica Store Munich. In practice, this doesn't bug me that much as I rarely focus to infinity with the type of photography I do, buuuuut on the flip side of that, the CLA and Lens are still under warranty, so if I were to get something checked, I'd prefer to do it now while I still don't have to pay out of pocket. 

I would just hate to be without the M6 and Lens again for potentially weeks + months only to discover that "one and/or both are within acceptable tolerances." Haha, so what do you guys think? 

 

2 hours ago, shawn2nd said:

I'd say it was def infinity, had to be a good 100m away at least haha

I think this is normal. I tried the same with my M9. First, I focused on a church tower at 300m. It was spot on, when at the infinity stop the focus patch was perfectly aligned.

Then I tried the corner of a house about 100m away. I had to focus just before  the stop (maybe a mm)  to get the images aligned.

So 100m does not qualify as infinity 300m or further does. Your M6 is a bit more accurate so you need to go even further. I would guess 500m would qualify as infinity for the M6.

See the tables @jaapv posted.
With your M6 (0,72) rangefinder, you are focusing as if you are using a 120mm tele lens on a SLR, no matter what lens is mounted. So it makes sense that you can see a small focus difference between 100m and for example 500m or beyond.

Make sure that if you focus on the moon, your focus patch is aligned when at the infinity stop. Then there is nothing to worry about.

Edited June 14, 2024 by dpitt

[shawn2nd]

46 minutes ago, jaapv said:

I'm a bit surprised that you used Kamera Express as a CLA option - it is a large international camera retail chain which farms out repairs to - ????

Errr my mistake, meant Kamera Service not Kamera Express

--

All in all I think I'm going to just not sweat it. My M11 came in today, so naturally I wanted to test the same theories from the M6 but on digital where I could instantly see the results. So threw the Summarit on the M11 and took the same photos, behavior-wise, I'm getting the same thing, focusing to hard stop was slightly out of focus in the viewfinder, maybe 1mm back to the left and the VF was in focus. 

So I took two shots of the same thing at the same exposure, one hard stop, one 1mm to the left, and honestly I can't tell a difference both look super sharp haha. So just gonna carry on, but thanks for the info guys. 

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[jaapv]

That was a good choice 🙂

If it bothers you, - which it wouldn't me-  you could give roller a minimal twist.

[adan]

3 hours ago, shawn2nd said:

I'd say it was def infinity, had to be a good 100m away at least haha

You need to test with something more like 1000m away, at a minimum. haha. 😆 The moon at dusk is an even better target.

Seriously - the Leica M RF (correctly calibrated, and with good eyesight) can (and needs to) distinguish between 100m, 300m and "infinity." Try it with a 135mm, or a 75 f/1.4, and that soon becomes apparent.

[raizans]

You know how some M2’s have the DOF indicators at the top and bottom of the rangefinder patch?

Someone did a test many years ago to see how much the double images in the rangefinder patch can be offset and photos still come out “in focus.” They made a chart for different focus distances, apertures, and focal lengths.

In most cases (less demanding situations), the double images don’t have to perfectly overlap. They can be a couple millimeters out of sync.

Edited June 15, 2024 by raizans

[lct]

59 minutes ago, raizans said:

You know how some M2’s have the DOF indicators at the top and bottom of the rangefinder patch?

M2 instructions manual:

leicaM2_manual_p16.pdf