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lct

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Posted (edited)

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15 minutes ago, lct said:

I must have leant this 20+ years ago thank you although i don't recall everything but what interests me is what in-camera difference(s) can explain that focus shift doesn't look the same with the same lens and everything else when the only variable is the camera.

The main differences in camera calibration are 

1. rangefinder calibration: if you’re focusing both cameras according to the rangefinder on the same subject, the resulting distance setting on the lens could be slightly different because of different rangefinder adjustment. 

2. flange focal distance (distance between the lens mount and the sensor or film plane): even when the lens has the same distance setting on both cameras, the focal plane could be slightly different (further or closer) because of varying flange distance between cameras. 

Both of these vary slightly between cameras, also between samples of the same model. 
 

But again, the focus shift is the same for both cameras. It is the focus accuracy at single apertures that differs. 
 

 

 

Edited by roelandinho
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3 minutes ago, jaapv said:

As said multiple times in this thread: you were just lucky with the adjustment on this specific camera and lens.

Luck again? Doesn't hold water to me sorry.

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1 hour ago, lct said:

Luck again? Doesn't hold water to me sorry.

In that case - read my posts and understand even if you are not a techie as you always claim 😉.
This lens and this camera are perfectly matched. I call that luck. Be happy and accept it - most users don't have this lucky combination.
The sensor alignement of your other camera is likely within the tolerance span but not perfectly matched to this particular lens.
The rangefinder adjustment is probably not relevant to this effect, as it is not of influence on the relationship between DOF and plane of focus which causes variations in the noticeability of focus shift.

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3 hours ago, roelandinho said:

Camera A cannot show less focus shift than camera B with the lens at the same aperture, because it's impossible to measure focus shift by looking at just one aperture. The only thing you can compare at a singe aperture is the amount of (focus-)error at that aperture. The error at that single aperture can be different for both cameras with the same lens, depending on camera calibration. For example, camera A could show more back-focus at f/2.8 than camera B at f/2.8. 

The focus shift of the lens is however the same on both cameras. To see this, take a series of pictures through all aperture values of a flat grass field or some other textured surface so you can clearly see the entire focus field. You should be able to determine the plane of best focus (a curve in the grass or texture) in each picture. You'll notice the focal plane moves further from the camera with each smaller aperture stop. 

I did take series pictures through all the apertures with both cameras.

That’s why I said I gave up. I don’t want to persuade anyone one way or the other 

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7 minutes ago, Warton said:

I did take series pictures through all the apertures with both cameras.

That’s why I said I gave up. I don’t want to persuade anyone one way or the other 

Same here. I did not ask anything in my OP but i'm now a bit more curious as to why focus shift or the effect of it looks reduced when using the Sonnar on the M11. I also thank good colleagues here who offered an explanation. Further examination could be interesting though.  I think of magnification that plays a role in DoF but i did not dig into this idea yet.

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9 minutes ago, lct said:

Same here. I did not ask anything in my OP but i'm now a bit more curious as to why focus shift or the effect of it looks reduced when using the Sonnar on the M11. I also thank good colleagues here who offered an explanation. Further examination could be interesting though.  I think of magnification that plays a role in DoF but i did not dig into this idea yet.

I cannot imagine why there would be less focus shift with M11 than with M10R. Can you make a controlled experiment that shows the difference in focus shift behavior?

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1 minute ago, SrMi said:

I cannot imagine why there would be less focus shift with M11 than with M10R. Can you make a controlled experiment that shows the difference in focus shift behavior?

If you have the courage, do it yourself please but i did not open this thread to demonstrate anything sorry. Just stating that my favorite 50 for portraiture has become the Sonnar on the M11 due to its apparently lower level of focus shift or effect thereof. It is not the same with all lenses though. Summicron 35/2 v4, Summilux 35/1.4 v2 or Summicron 50/2 v4 still show the same level of focus shift on M11 and M240 as far as my bodies are concerned but i am too lazy to engage in a controlled experiment, sorry again.

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22 minutes ago, lct said:

If you have the courage, do it yourself please but i did not open this thread to demonstrate anything sorry. Just stating that my favorite 50 for portraiture has become the Sonnar on the M11 due to its apparently lower level of focus shift or effect thereof. It is not the same with all lenses though. Summicron 35/2 v4, Summilux 35/1.4 v2 or Summicron 50/2 v4 still show the same level of focus shift on M11 and M240 as far as my bodies are concerned but i am too lazy to engage in a controlled experiment, sorry again.

I am curious about your observations, and I am getting curious about the Sonnar as you and others have shared very positive opinion about that lens.

If I get it, I will run the tests. 

Important is that you know how Sonnar works for you.

 

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17 minutes ago, SrMi said:

I am curious about your observations, and I am getting curious about the Sonnar as you and others have shared very positive opinion about that lens.

If I get it, I will run the tests. 

Important is that you know how Sonnar works for you.

As you say but don't forget that this lens suffers from focus shift if you are interested. You may wish to try it in both variants calibrated for f/1.5 and f/2.8 in such a case. I did the same 10 years ago when i bought the lens and i chose f/1.5 then but it was on the M240 and i never tried the variant calibrated for f/2.8 on the M11.

 

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42 minutes ago, lct said:

As you say but don't forget that this lens suffers from focus shift if you are interested. You may wish to try it in both variants calibrated for f/1.5 and f/2.8 in such a case. I did the same 10 years ago when i bought the lens and i chose f/1.5 then but it was on the M240 and i never tried the variant calibrated for f/2.8 on the M11.

Thank you for the warning. I assume the default calibration is f/2.8, and you must send it in to get the f/1.5 calibration. Of course, that does not matter if you are focusing with EVF/LCD ar working aperture.

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I don't know how Cosina maganages the matter nowadays but indeed there is no focus shift issue when focusing in LV mode at working aperture as you say.

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1 hour ago, SrMi said:

Thank you for the warning. I assume the default calibration is f/2.8, and you must send it in to get the f/1.5 calibration. Of course, that does not matter if you are focusing with EVF/LCD ar working aperture.

I bought a new 50 Sonnar ZM about four years ago and that one seems to be calibrated for perfect focus at f/2, which is a good compromise for me. I prefer the rendering of this lens at f/2 and f/2.8 to wide open anyway. I find it quite easy to compensate the focus shift while focusing at smaller apertures. 

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Posted (edited)
6 hours ago, roelandinho said:

I bought a new 50 Sonnar ZM about four years ago and that one seems to be calibrated for perfect focus at f/2, which is a good compromise for me. I prefer the rendering of this lens at f/2 and f/2.8 to wide open anyway. I find it quite easy to compensate the focus shift while focusing at smaller apertures. 

Ditto here. I just try to avoid f/4 and f/5.6 in RF mode as those are apertures where the shift is the more visible and is not compensated with DoF but the Visoflex 2 works fine at all apertures with this lens anyway. Interesting that the current variant is calibrated for f/2 BTW. I could give it a try eventually although f/2 is my favorite aperture on portraits and i would not like them to be too sharp then. Matter of taste as usual. Thanks for sharing.

Edited by lct
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On 5/2/2024 at 6:19 PM, jaapv said:

A sensor is not a focal plane  Nobody said that a sensor moves…. The only one who brought this up is you...

The focal plane is the collection of focus points at the distance between your camera lens and the perfect point of focus. A sensor is, well, a sensor. When the two coincide your image is in focus. 

https://mastinlabs.com/blogs/photoism/understanding-focal-plane-in-photography

Actually, Jaap, I seem to recall that the only camera with a moving sensor was a Contax(?) which had some built in focusing mechanism - probably wrong, I’m sure you’ll tell me.  If you read my post as saying that a sensor could or should move, I clearly didn’t express myself well enough - God knows my post was long enough.  So, for the record, we don’t disagree - the focal plane is where the image is at best focus, and hopefully the film, sensor and focal plane marking on the topdeck all coincide.

Focal plane, depth of focus, depth of field, focus shift … it all gets so confusing when you try to express yourself accurately, knowing some member of the forum will take issue with the point you weren’t trying to make.

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On 5/1/2024 at 9:28 PM, IkarusJohn said:

I’m still not with you.

The focal plane is at the sensor - it used to be marked on the top deck.  How does that move when using the rangefinder?

The depth of focus is the depth of the plane of best focus at the focal plane - not such a problem with the thick emulsion on film, more of a problem with a digital sensor.  It’s quite different from depth of field and focus shift.  Focus shift is when the image projected by the lens is at the focal plane at, say, f/2 and then moves away as the lens is stopped down, making the image at the focal plane out of focus, until the the depth of field brings the image back into acceptable focus - at f/5.6 or smaller.

Famously a problem with the 35 Summilux ASPH (first version) and the f/1 Noctilux.

Now, I know that some wil quibble with that explanation, but my point is, I’m not sure I follow how the rangefinder has any impact on the lens, or the depth of focus, or the focal plane, for that matter.  The focal plane stays in the same place.  It’s the plane of best focus that shifts as the lens is stopped down.  That’s the problem …

Ooops, I seem to be repeating myself.

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Posted (edited)
2 hours ago, IkarusJohn said:

I seem to recall that the only camera with a moving sensor was a Contax(?) which had some built in focusing mechanism - probably wrong

Only slightly - it was a 35mm-film Contax, the AX. 1996.

The camera was a pudgy beast, since the entire film-plane/shutter/viewfinder unit had to slide forwards and backwards 1 cm <-----> inside the large outer casing. I.E. a "film-plane-focusing" camera. Of note, however, so was the original 1940s-50s Mamiya Six 6x6 folding camera.

https://www.iconpublications.com/photon/apr96/contaxaxe.html

http://camera-wiki.org/wiki/Mamiya_Six

Didn't last long - Contax soon replaced it with a full-AF 35mm SLR system (NX) with all-new Zeiss AF lenses (alongside their 645). And died shortly thereafter

I used the Contax RX around that time - a halfway step to the AX in that it provided "manual-focus confirmation" without actually moving anything itself.

AF detector in the mirror-box, and green dot in the viewfinder  •  - but the user still had to turn the lenses focusing ring by hand, until the green dot lit up. (Which I ignored, and just used the split-image prism in the focusing screen). But a very nice "number-engraved 'analog' knobs and dials for everything" film SLR, sort of like a really big Fuji XT-series.

http://camera-wiki.org/wiki/Contax_RX

https://www.dpreview.com/reviews/fujifilm-x-t5-in-depth-review

 

Edited by adan
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I still have and occasionally use my RX. AX, from what I've understood over time, often failed to achieve accurate focus, but was an interesting early attempt at autofocus.

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At what point - and why - did this thread become a discussion about sensor-placement etc...etc...etc...?

Just curious as to why this potentially very interesing thread was destroyed.

Philip.

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