Stop down focusing - Advice

[vjbelle]

That is quite weird, because usually the nearer your target is, the shallower the DOF. I would rather assume that with objects standing further away the DOF would be greater and thus focus errors more forgiving.

What you say is very true and certainly would apply if the focus was slightly off at the wide open aperture and there was 'NO' focus shift. The added DOF would probably completely mitigate the mis-focus. However with the shift I am experiencing the DOF is increased but shifted behind the lens and, of course, also in front - but not enough to make my target sharp.

Victor

 

[vjbelle]

Victor, perhaps your lens is in need of calibration?

- Marc

I don't claim to be a lens design expert but I don't know what calibration would cure. All I am doing is focusing and then ultimately stopping down. If calibration could cure shifting then I'm all in but I don't think there is a cure for shifting.

If you have access to a LensAlign and a 50mm Cron take some images stopping down when focused at f2.0. My lens starts its gradual backfocus until f4.0 where it makes a big leap.... never saw anything like that before. Anyway I have my workaround.... focus at f3.5 - stop down to whatever and all is fine.

Victor

 

[D&A]

Victor, by focusing at f3.5 and then stopping down, do fortunately works for a camera where you can implement live view when focusing. Unfortunately when using a camera like the Leica M9 and others without the benefit of live view, there is no way to circumvent focus shift unless one purposely misfo vises in front of the subject to compensate.

I'm surprised to hear that your cron has so much focus shift. I was under the impression that most 50mm crons exhibit little if any. I assume your lend is spot on when shot wide open? Have you asked other users of the 50mm cron what their lenses are like with regards to focus shift?

Dave (D&A)

 

[tashley]

I don't claim to be a lens design expert but I don't know what calibration would cure. All I am doing is focusing and then ultimately stopping down. If calibration could cure shifting then I'm all in but I don't think there is a cure for shifting.

If you have access to a LensAlign and a 50mm Cron take some images stopping down when focused at f2.0. My lens starts its gradual backfocus until f4.0 where it makes a big leap.... never saw anything like that before. Anyway I have my workaround.... focus at f3.5 - stop down to whatever and all is fine.

Victor

Victor, you are entirely correct. Calibration applies only to Phase Detect Auto Focus and the only way to accurately focus a lens with shift is to use either live view or Contrast Detect, at the shooting aperture. I also totally believe you that your focus shift is as strong as you say: I don't have that lens, but I have had other Leica glass with quite serious shift. This can be compounded by the shape of the field of focus and the way it changes with subject distance and aperture.

 

[jlm]

since the M lenses are focused in the MM, Mx, only by the rangefinder method, how have people been dealing with the focus shift?

 

[fotografz]

since the M lenses are focused in the MM, Mx, only by the rangefinder method, how have people been dealing with the focus shift?

When shooting available light, the camera's Live View menu item is set to Setting Effect On … what you see is what you get. So a properly exposed image is what you use to focus on no matter what aperture is selected. There is no shift, because you are focusing at working aperture.

In a dark studio where strobes are providing the light only for a nano second, you may be stopped down so far with a higher shutter speed and a low ISO, that the ambient light in the studio is totally black in the viewfinder. Then you have to change the Live View menu item to "Setting Effect Off" so you can see to focus.

- Marc

 

[jlm]

my question was more about the Leica MM, M9 environment, where presumably the same focus shift at differing apertures would occur, but there is no live view. i don't recall hearing so much about this except maybe with the noctilux

 

[tashley]

John, there was a lot of this stuff around when the M8 first appeared an people started to discover the pains of focus shift in a way that had been far less evident in the days of film. For example, Leica redesigned the 35 Lux because the pre-FLE version had such chronic focus shift. In general, for most affected lenses, people either switched or learned to live with it - which often meant testing their kit carefully to see what degree of shift happened at different subject distances and apertures and then tweaking their focus accordingly. But it was too hit and miss for me so I sold any lens I had whose shift outran its DOF as you stopped down.

 

[Shac]

That's what I found too - yesterday tested a Nikkor 105 AiS and found focus shift at around 3' on the A7 - using live view of course dealt the problems

 

[D&A]

John, refer to one of my previous posts above. With rangefinder cameras like the M9 or MM, you can sort of try compensating your focus (focus slightly in front of your subject) when shooting with a lens with known focus shift. This way when stopping down a bit, and the lens starts back focusing (focus shifting), your subject hopefully will be in focus. It's a crap shoot and sort of what Tim was suggesting.

The other thing you can do is have the lens optimized for an f stop slightly stopped down rather than wide open. This will give a larger percentage of shots in focus when shooing between wide op en and f5.6. I describe the theory in one of my posts above.

Dave (D&A)

 

[fotografz]

John, refer to one of my previous posts above. With rangefinder cameras like the M9 or MM, you can sort of try compensating your focus (focus slightly in front of your subject) when shooting with a lens with known focus shift. This way when stopping down a bit, and the lens starts back focusing (focus shifting), your subject hopefully will be in focus. It's a crap shoot and sort of what Tim was suggesting.

The other thing you can do is have the lens optimized for an f stop slightly stopped down rather than wide open. This will give a larger percentage of shots in focus when shooing between wide op en and f5.6. I describe the theory in one of my posts above.

Dave (D&A)

I can confirm that theory Dave. It is what I had done to my non FLE 35/1.4 ASPH, and now I rarely experience a miss-focus due to shift when shooting with M9, MM or the M240 I briefly tested recently.

- Marc

 

[MCTuomey]

I can confirm that theory Dave. It is what I had done to my non FLE 35/1.4 ASPH, and now I rarely experience a miss-focus due to shift when shooting with M9, MM or the M240 I briefly tested recently.

- Marc

Dave or Marc, question re the optimization, which aperture do you suggest? I tested my recent non-FLE Lux 35 asph on a make-shift DOF chart and it looks like f/2 to f/2.8 would be about right, maybe closer to f/2. What did you spec?

 

[fotografz]

Dave or Marc, question re the optimization, which aperture do you suggest? I tested my recent non-FLE Lux 35 asph on a make-shift DOF chart and it looks like f/2 to f/2.8 would be about right, maybe closer to f/2. What did you spec?

I did f/2.

- Marc

 

[MCTuomey]

I did f/2.

- Marc

thank you marc

 

[D&A]

Completely agree with Marc! Generally for the Leica 35mm f1.4 Lux Asph (non FLE), optimize for f2. I had an acquaintance who I was assisting in determining what would be best for his sample, and it turned out to be f2.4 (yes between f2 and f2.8).

Dave (D&A)

 

[MCTuomey]

Completely agree with Marc! Generally for the Leica 35mm f1.4 Lux Asph (non FLE), optimize for f2. I had an acquaintance who I was assisting in determining what would be best for his sample, and it turned out to be f2.4 (yes between f2 and f2.8).

Dave (D&A)

and thanks to you dave. i'm corresponding with DAG to see when the work might be done.