Field curvature? Or something else?

[Rick]

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I know only Mr Ashley as the discoverer of the "boricron" 28/2 sorry but in case of field curvature and focussing in the center of the frame the subject matter won't be sharp if it is not in the center itself unless DoF is wide enough to compensate the effect. Easy to check at fast aperture with everyone's body. In such circumstances the RF's accuracy is always inferior to a modern EVF with moving focus patch and focus magnification in my modest experience but i'm not a reviewer.

 

 

lct - I know you believe this is true, but it isn't.  The RF is the most accurate way to focus on the M.  EVF is subject to deep DOF in focus peeking.  How can you find the POF when the DOF displayed in focus peeking is so deep?  And, it is even deeper when you stop down.

 

The RF focus is razor sharp.  And the RF will place the focus point within the DOF so the whole image plane will be best compensated for the field curvature of the lens.  

 

Try and focus the Macro 90 Elmar with the focus peeking and the EVF.  It is not possible to get it right.  The only way to do it is with the goggles and the RF.

 

Rick

[lct]

It is not a matter of focus peaking Rick. I never use those things. It is a matter or focus magnification and it works very well you can trust me even at slow apertures. I agree that the RF is faster and there are indeed circumstances where the rangefinder is more accurate, typically with wides at slow apertures but DoF is wide so there is no significant problems of field curvature then actually. You know i use the little 90/4 macro and almost all my (too) many M & R lenses with a Sony A7s mod now so i begin to know a bit how a good EVF can work and it was almost the same with my little Fuji X-E2 previously. My only non-M/R lens is a Fuji wide (i don't recall the FL...) that i used a couple of times. Its 100% EVF, 99% manual focussing, and 90% stop down focussing for me with those cameras. As you quoted the 90/4 macro, here's a snap that i shot with it at f/8 on the Fuji. I almost won the Pulitzer prize with it . No rangefinder. No focussing at f4. Just f/8, focus and shoot. FWIW.

 

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[lct]

Just shot this other masterwork for you. A7s mod, Elmar 50/2.8, about 50 cm focus distance, 5000 iso, stop down focussing at f/11. Who cares about focus shift or field curvature? Suffice it to move the focus patch and focus on the VF that's all. (no Leica body handy sorry). Slower process yes. Inaccurate, definitely no.

 

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[edwardkaraa]

My recommendation for focusing lenses with pronounced field curvature with a EVF is to turn off peaking, crank up sharpness to the maximum, and focus with the entire frame without magnification (as in compose the shot then focus). I still find a well calibrated RF to be the fastest and most accurate but I'm getting excellent results and almost as fast with the above described settings.

Edited May 7, 2016 by edwardkaraa

[darylgo]

When I look at mtf curves for your lens it shows 50% or above for 12mm, after that the curves seperate giving astigmatism and less contrast/sharpness.  So your image should (theoretically) look sharp across 2/3 of the image, with a gradual fall off toward the edges and corners worse.  The first thought is the lens is not truly focused at infinity, if so, then likely the lens needs adjustment.  The other issue could be decentering.

[Nordvik]

100% from upper left corner with M9.

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[Nordvik]

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Two more: 

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[Nordvik]

All were focused at infinity and at 5,6.

[Nordvik]

Two of them at infinity and 2,0:

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[Nordvik]

They are all 50mm.