50 Lux Black Chrome - Focus shift?

[dkmoore]

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I recently acquired the 50 Lux BC and have been playing around with it during quarantining. I'd like to better understand the focus plane. For instance, when I focus on the M on the book below, the area in focus extends much closer to me. You can see the focus drop off by the E behind the M is much closer. I have other lenses that are about 50/50 in front and behind.

I still get nice sharp eye balls most of the time but it is very clear that the focus stops very soon after the intended target yet I have some focus in front.

Is this a type of focus shift inherent to the 50 Lux? I don't think it is lens calibration?  (used tripod. Heavy crop for illustration purposes.) Just trying to better understand. 

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[a5m]

Speaking with the head tech at Leica I was told the standard is to adjust focus with the lens set to its widest aperture and have the focus 3/4 towards the front and 1/4 behind. This is so that as the lens is stopped down the DoF drifts backwards and you end up with accurate focus throughout the aperture range.

It's possible it was adjusted like this from the factory or had a recent trip to Leica.

[dkmoore]

14 minutes ago, a5m said:

Speaking with the head tech at Leica I was told the standard is to adjust focus with the lens set to its widest aperture and have the focus 3/4 towards the front and 1/4 behind. This is so that as the lens is stopped down the DoF drifts backwards and you end up with accurate focus throughout the aperture range.

It's possible it was adjusted like this from the factory or had a recent trip to Leica.

Interesting. I had not heard that. I purchased brand new and the outer box still had the white stickers closing all. So, it must have been adjusted as such from Wetzler. 
 

is that just for the 50 Lux? None of my other lenses seem to exhibit this behavior. 

[a5m]

No, according to the tech it's the same for all lenses. At the time we were discussing my 75 Summilux and Noctilux F1, and I had asked for the focus to be adjusted 50/50.

What you describe falls in line with what the tech told me, so I'm assuming your lens was adjusted that way at Wetzlar.

It's possible the focus of your other lenses has 'drifted' over time? Or if purchased used their focus was previously adjusted. Or maybe it's just the inherent variances of the rangefinder system.

[Bo-Sixten]

My 50 Lx BC behaves just like yours, dkmoore. At close focus like your example this is not a problem, but the behaviour is pronounced when focusing at longer distances. Test it wide open at 15-20m to see how it actually focuses. If within margins for hitting focus, the good thing is that you get fabulous bokeh even when stopping down a bit - almost Noctilux good.

My problem is having other lenses with wide apertures and slight back focus in comparison, e.g. 90APO, 75 Lx, 50 Noct. When I adjust my RF in the camera (M10, M10M) for these lenses, the 50 BC will front focus and not hit the right focus. I have tried to find a "middle way" in RF adjustment and to adapt my focussing method to a specific lens with "problem". I focus from infinity and down for lenses with front focus and from close distance and up with back focus lenses. And no fiddling around with the focus ring - just one move. The focussing margins are that small.

Hope this helps your testing.

Edited May 4, 2020 by Bo-Sixten

[250swb]

5 hours ago, dkmoore said:

 I have other lenses that are about 50/50 in front and behind.

 

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Did you use LV to focus, because I suggest you aren't focused on the M but somewhere between the A and I in 'Remains' (look at the 'NN' below it). This would resolve two things, all lenses have a bias for having more DOF behind the focus point than in front, it is basic lens lore and is taught in any book on photography, 50/50 is impossible. So if you are focused on the A or I the focus drops off sooner in the foreground than the background and this is demonstrated in the photo. The second point would be that LV accommodates for focus shift, the rangefinder doesn't, so if you are sure as sure can be you had the rangefinder perfectly lined up on the M then either it's focus shift or a calibration issue.

Edited May 4, 2020 by 250swb

[jaapv]

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Is this the ASPH? That lens has a floating element that influences the focusing at close distances. It is a well known issue that some new lenses need readjustment.

[dkmoore]

3 hours ago, 250swb said:

Did you use LV to focus, because I suggest you aren't focused on the M but somewhere between the A and I in 'Remains' (look at the 'NN' below it). This would resolve two things, all lenses have a bias for having more DOF behind the focus point than in front, it is basic lens lore and is taught in any book on photography, 50/50 is impossible. So if you are focused on the A or I the focus drops off sooner in the foreground than the background and this is demonstrated in the photo. The second point would be that LV accommodates for focus shift, the rangefinder doesn't, so if you are sure as sure can be you had the rangefinder perfectly lined up on the M then either it's focus shift or a calibration issue.

I focused on the front of the M. i also conducted this test with live subjects (wife and kids) and the eyes are in focus. But the DOF behaves opposite of what you mention and what I’m used to. It is about 3/4 in front and 1/4 behind. With live view, to your point, there is no issue. 
 

In live view I can control exactly where the DOF lands and can make it 50/50 exactly as you point out.  But, I am a rangefinder guys and use the OVF 99% of the time because it is most fun for me.
 

I’ll try the lens on the M10M tonight to see if I get the same results. It pains me to send it to Leica as last time they tried to adjust lenses for me they wrecked a couple. Maybe I’ll send to DAG. 

[dkmoore]

2 hours ago, jaapv said:

Is this the ASPH? That lens has a floating element that influences the focusing at close distances. It is a well known issue that some new lenses need readjustment.

Yes, it is the limited edition BC of 500+ (lol). 
 

Agreed, I had similar challenges with other copies of the non limited to 500+ versions. That said, I wasn’t able to still get critical focus. That is why I was thrown off. The other lenses were just off. For instance, if I focused on eyes the teeth or nose would be sharpest. To me, that is front focus. This seemed more like a shift. 

[dkmoore]

I’ll run another test tonight with the 50 Lux on M10M and I’ll test the 50 APO on the M10P. 
 

that should narrow down whether or not it is 100% the lens. 

[farnz]

I note that in your test set up at the top of the page the camera appears to be pointed down.  Since the lens cell is circular it follows that the depth of focus and drop-off will also be circular (cylindrical) and not planar.  Might it be that the Y-plane is affecting your interpretation where you appear to only be considering in the X- and Z-planes?  Just a thought.

Pete.

[dkmoore]

5 hours ago, farnz said:

I note that in your test set up at the top of the page the camera appears to be pointed down.  Since the lens cell is circular it follows that the depth of focus and drop-off will also be circular (cylindrical) and not planar.  Might it be that the Y-plane is affecting your interpretation where you appear to only be considering in the X- and Z-planes?  Just a thought.

Pete.

Yes, the thought crossed my mind but then it shut down due to complexity (my brain that is). 

Are you saying that if I ensured the camera and focus point are level, the results may shift in favor of the lens? Or potentially negative depending if there is in fact a calibration issue?

[farnz]

4 minutes ago, dkmoore said:

Yes, the thought crossed my mind but then it shut down due to complexity (my brain that is). 

Are you saying that if I ensured the camera and focus point are level, the results may shift in favor of the lens? Or potentially negative depending if there is in fact a calibration issue?

I'm simply pointing out that depth of focus is a three dimensional effect but using the (linear) text on the book to judge what's in or out of focus is only really considering the focus depth in two dimensions (the horizontal X-plane and the 'depth' z-plane).  The Y-plane is the vertical plane.  

Mentally drawing corner to corner lines indicates that they would cross above the text so it's not at the centre point of where the lens is pointed.  This is likely to mean that the word "remain" is straddling the south-west and south east quadrants of the 'focus cylinder' instead of crossing its centre point where it's dropping in and out of focus might be different and your interpretation of the focus area extending more towards you than away from you might not be correct. 

Additionally the book is tllted at an angle to the camera, which might accentuate in and out of focus areas.  This could mean that what you're interpreting as 'receding focus' might actually be a result of the angle of the book at any point. 

All of the above *could* be leading you to the conclusion that there's more in focus in front than behind where you believe the point of actual focus to be, which might not be the case in reality.  Testing requires the elimination of as many variables as practicable to try to get to the point where the only variables left are the ones that the tester adjusts during the test and repeatable results are achieved from which meaningful conclusions can be drawn.  (My apologies if this sounds like lecturing, it's not intended to be, I couldn't think of a way to put it any more clearly.)

Pete.

[dkmoore]

5 hours ago, farnz said:

I'm simply pointing out that depth of focus is a three dimensional effect but using the (linear) text on the book to judge what's in or out of focus is only really considering the focus depth in two dimensions (the horizontal X-plane and the 'depth' z-plane).  The Y-plane is the vertical plane.  

Mentally drawing corner to corner lines indicates that they would cross above the text so it's not at the centre point of where the lens is pointed.  This is likely to mean that the word "remain" is straddling the south-west and south east quadrants of the 'focus cylinder' instead of crossing its centre point where it's dropping in and out of focus might be different and your interpretation of the focus area extending more towards you than away from you might not be correct. 

Additionally the book is tllted at an angle to the camera, which might accentuate in and out of focus areas.  This could mean that what you're interpreting as 'receding focus' might actually be a result of the angle of the book at any point. 

All of the above *could* be leading you to the conclusion that there's more in focus in front than behind where you believe the point of actual focus to be, which might not be the case in reality.  Testing requires the elimination of as many variables as practicable to try to get to the point where the only variables left are the ones that the tester adjusts during the test and repeatable results are achieved from which meaningful conclusions can be drawn.  (My apologies if this sounds like lecturing, it's not intended to be, I couldn't think of a way to put it any more clearly.)

Pete.

I didn't take it as lecturing at all! It is very helpful in fact.  I provide a redo test today on tripod with the 50 Lux and another round with the 50 APO (top - darker) on tripod. Almost exactly the same results, which is interesting. So, that tells me that the book angle and whatever other angle issue is as you state, probably causing this. 

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Edited May 4, 2020 by dkmoore

[dkmoore]

What I am learning is that this is not how you test a new lens! M10M with 50 Lux BC and almost EXACT same results. Maybe the M10 is ever so slightly more front focused.

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[dkmoore]

Picture of eye ball. Looks pretty good to me at 125s. Same results I was getting on tripod. Probably a false alarm.

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[dkmoore]

5 hours ago, farnz said:

I'm simply pointing out that depth of focus is a three dimensional effect but using the (linear) text on the book to judge what's in or out of focus is only really considering the focus depth in two dimensions (the horizontal X-plane and the 'depth' z-plane).  The Y-plane is the vertical plane.  

Mentally drawing corner to corner lines indicates that they would cross above the text so it's not at the centre point of where the lens is pointed.  This is likely to mean that the word "remain" is straddling the south-west and south east quadrants of the 'focus cylinder' instead of crossing its centre point where it's dropping in and out of focus might be different and your interpretation of the focus area extending more towards you than away from you might not be correct. 

Additionally the book is tllted at an angle to the camera, which might accentuate in and out of focus areas.  This could mean that what you're interpreting as 'receding focus' might actually be a result of the angle of the book at any point. 

All of the above *could* be leading you to the conclusion that there's more in focus in front than behind where you believe the point of actual focus to be, which might not be the case in reality.  Testing requires the elimination of as many variables as practicable to try to get to the point where the only variables left are the ones that the tester adjusts during the test and repeatable results are achieved from which meaningful conclusions can be drawn.  (My apologies if this sounds like lecturing, it's not intended to be, I couldn't think of a way to put it any more clearly.)

Pete.

Changed the angle and showing same result. However, I just realized I accidentally moved the BC to 2.8. 

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Edited May 5, 2020 by dkmoore

[a5m]

13 hours ago, dkmoore said:

It pains me to send it to Leica as last time they tried to adjust lenses for me they wrecked a couple. Maybe I’ll send to DAG. 

Can you elaborate on this?

I'm glad you're figuring out what's going on with the lens. Looks like everything is copacetic.

[dkmoore]

Same result on M10M at 1.4 so it most certainly has something to do with the angle and I'd imagine because the results replicate themselves almost exactly that both cameras and both 50s are likely spot on focus wise. Probably a bad way to deduce that! :  )- 

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Hallo,

Look here: Leica M

[dkmoore]

And last but not least another eye ball picture. M10M & 50 Lux. I think I am good to go.

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