50mm Summicron Collapsible backfocusing

[bcapphoto]

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Now that I have a digital M, I'm able to test something I haven't been able to with my My6 - at least not quickly, easily and consistently. 

My 50mm Summicron Collapsible seems to be backfocusing a bit. On this image, I had focused on the batteries with the rangefinder patch, yet the focus is behind them. 

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On this one, I spaced the batteries out by 1-2 inches each and focused on the 2nd from the right. You can see that critical focus actually seems to be on the battery to the far left. 

Does anyone have experience with this? Should I send it away to get callibrated?

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[farnz]

16 minutes ago, bcapphoto said:

Does anyone have experience with this? Should I send it away to get callibrated?

Are you certain that it's not rangefinder calibration in your digital M?  If you have another lens you can check this of course and you might save yourself time and money by sending the right bit for calibration if it needs it.

Pete.

[bcapphoto]

11 minutes ago, farnz said:

Are you certain that it's not rangefinder calibration in your digital M?  If you have another lens you can check this of course and you might save yourself time and money by sending the right bit for calibration if it needs it.

Pete.

Yea - I've been suspecting the same thing on my M6. A lot of my shots, wide open, have been backfocused. I did the same test with my 35mm Summicron and it's all good. 

[jaeger]

Lens this old could have been calibrated 50 years ago, I would check the camera instead. 

[bcapphoto]

24 minutes ago, jaeger said:

Lens this old could have been calibrated 50 years ago, I would check the camera instead. 

Nah, my 35mm Summicron is fine on both this body and my M6. The 50mm is off on both this and my M6. I am just able to test it more quickly on my M240. 

[tommonego@gmail.com]

Send either camera and the lens to a repair place, they should be able to calibrate the lens to the camera. It is an old lens and may need some TLC.

[a.noctilux]

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Hello Bcap,

With liveview of your M240, you may be able to be sure that it's not the RF calibration of your M240/M6.

35mm lens has more deep of field at "same situation" than 50mm as you know, so a bit of RF error can be covered by dof

Put your M240 on tripod, then focus with the RF, check with LV with x10 magnification (with front button + rear wheel).

If the test has discrepency, then you can "see" if only the Summicron must be sent for calibration or the M240+Cron.

[oldwino]

That desk is shockingly uncluttered. I’d be embarrassed to show mine. 
 

While the camera RF is the usual suspect, I’ve has a few lenses over the years that needed calibration. 

[BrianS]

At one point I owned 5 Collapsible Summicrons. I'm down to 3- one perfect glass M-Mount and two Hot-Glass early Summicrons-, they all focus perfectly used wide-open on my M9.

The 35mm Summicron has much more depth of field. "In the Day" you would walk the camera and set of lenses to a repair shop to have "Zeroed", camera and lens brought into agreement. These days- you send the camera and lenses in to be calibrated. They will probably calibrate the camera first, any error with the Summicron- then adjust it.

Edited October 11, 2020 by BrianS

[astrostl]

18 hours ago, a.noctilux said:

Hello Bcap,

With liveview of your M240, you may be able to be sure that it's not the RF calibration of your M240/M6.

35mm lens has more deep of field at "same situation" than 50mm as you know, so a bit of RF error can be covered by dof

Put your M240 on tripod, then focus with the RF, check with LV with x10 magnification (with front button + rear wheel).

If the test has discrepency, then you can "see" if only the Summicron must be sent for calibration or the M240+Cron.

100% this. I have a Datacolor SpyderLensCal SLC100 and my first steps would be to tripod-test multiple lenses with live view + rangefinder to determine if it was the body or the lens. And if it was the rangefinder body alignment, I'm crazy enough to attempt it myself but would probably go to DAG before Leica if sending out just to expedite.

[darylgo]

The lens can be focused from two directions, infinity to close or the opposite. Try focusing your 50mm both ways, stop when you reach proper rangefinder alignment. Many of my lenses are one side or the other, there’s slight play in the rangefinder alignment, lenses, my eyes or all of the above.  

[jaapv]

You must make it a habit to  focus  from the same direction always, infinity is most practical. Leica lenses are made to very high precision, but even then they will inevitably exhibit a (very small). amount of gear lash. This advice has been valid since 1954.

[darylgo]

10 hours ago, jaapv said:

You must make it a habit to  focus  from the same direction always, infinity is most practical. Leica lenses are made to very high precision, but even then they will inevitably exhibit a (very small). amount of gear lash. This advice has been valid since 1954.

My lenses turn both ways.😁

[jaapv]

Yes, but they focus differently depending on the way you turn them. Not much, but if you go for critical focus it is relevant.  Gear lash is the addition of tolerances that will make for a small amount of play throughout the focusing system. It has been a well-known phenomenon to rangefinder photographers for many decades. Thus the advice has always been: Focus from infinity, do not go back and forth, just turn to coincidence.

[Good To Be Retired]

Firstly, I would suggest a much different testing setup.  Tripod, bright daylight, self timer or cable release, PROPER test target around 8 feet distant.  Lens wide open, unless you never shoot wide open in real life.  In that case you might consider using the aperture you favor.

Make an exposure with Live View (assuming your camera supports this) at 100% magnification.  This is your gold standard.

Manual focus by turning the lens from BOTH directions.  You may or may not notice a different point of focus depending on direction of focus.

Repeat several times.

You may get exactly the same results anyway, but it's best to remove as many sources of potential error in testing as possible.  It's easy to cause yourself a lot of unnecessary grief by not testing rigorously (don't ask how I know this  )

Edited October 13, 2020 by Good To Be Retired

[darylgo]

3 hours ago, jaapv said:

Yes, but they focus differently depending on the way you turn them. Not much, but if you go for critical focus it is relevant.  Gear lash is the addition of tolerances that will make for a small amount of play throughout the focusing system. It has been a well-known phenomenon to rangefinder photographers for many decades. Thus the advice has always been: Focus from infinity, do not go back and forth, just turn to coincidence.

Makes perfect sense, except in practical use.   Coincidence takes place over a range of the ring movement, very slight movement doesn't change coincidence, yet will change focus and that change can make the difference between perfect focus and slightly less than perfect.  When taken into consideration the lens will be focused perfectly when focused from infinity or close with a stop at first coincidence.  Furthermore, a lens that is poorly calibrated can be focused perfectly by measuring the difference and giving it a slight turn in the necessary direction after coincidence.....albeit with practice.   

[farnz]

1 hour ago, darylgo said:

Furthermore, a lens that is poorly calibrated can be focused perfectly by measuring the difference and giving it a slight turn in the necessary direction after coincidence.....albeit with practice.

'Guess-focussing' based on muscle memory?  I think I'd prefer the sway-back technique to that although I'd rather have the lens properly calibrated than either.

Pete

[jaapv]

3 hours ago, darylgo said:

Makes perfect sense, except in practical use.   Coincidence takes place over a range of the ring movement, very slight movement doesn't change coincidence, yet will change focus and that change can make the difference between perfect focus and slightly less than perfect.  When taken into consideration the lens will be focused perfectly when focused from infinity or close with a stop at first coincidence.  Furthermore, a lens that is poorly calibrated can be focused perfectly by measuring the difference and giving it a slight turn in the necessary direction after coincidence.....albeit with practice.   

That is incorrect. Coincidence has two aspects: The coincidence we can see, due to the resolving power of our eye, that is indeed a range, and true coincidence, that is when the contrast of the RF patch suddenly increases, which is far more critical. See my post on RF focusing in the FAQ.

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[darylgo]

And who is the latter for?  

[darylgo]

2 hours ago, farnz said:

'Guess-focussing' based on muscle memory?  I think I'd prefer the sway-back technique to that although I'd rather have the lens properly calibrated than either.

Pete

Properly calibrated is preferred. New Jersey requires two visits or more, six months can pass. I can learn the lenses focusing traits in 30 minutes or use the evf  (not preferred) for critical dead-on wide-open perfectly focused images.... if the cat cooperates. 😁