[Klaus]

Technically it is nonsense to produce an MTF chart when ignoring the field curvature. However, it would still be a qualitative presentation method which shows when/how the field curvature is eventually masked by the depth-of-field. The question is how much value there is in this (as opposed to providing just a textual guidance). 

In case of the mentioned Samsung lens, you can at least notice that the depth-of-field is insufficient at mainstream aperture settings. Now, as you mentioned we could only do that for the object magnification ratio that we are using.

 

A plot is possible but would require an extra workflow - thus rather than keeping the magnification constant, we would need to move backward/forward and measured the different distances. I am not so sure whether I'd like to follow that path in terms of required efforts. Measuring flare has a higher priority (well, the new portal comes first once Markus manages to free some time again for PZ).

[Brightcolours]

Can/will the field curvature not change in certain lenses with different focus distances? 

[Klaus]

Can/will the field curvature not change in certain lenses with different focus distances? 

 

Yes, a guidance for everything below 1:10 magnification would be a different story for sure. But that's also true for the MTFs.

[Guest]

In real life there is a big difference: if corners are blurry, they are blurry. Like the extreme corners of my(the) EF 35mm f2. If there is some field curvature, chances are there is something sharp in corners, because a scene usually is deep (3D).

Can you give examples where the field curvature from that lens gives you problems? Which focal length?

When I look at image samples taken with that lens, I only notice the CA in the corners, CA which is easily corrected.
<a class="bbc_url" href="https://pixelpeeper.com/lenses/?lens=13192">https://pixelpeeper.com/lenses/?lens=13192</a>

A typical example would be a landscape with mountains (to have details in the upper corners at infinity), or even an architecture shot of a large flat building at some distance.


Several copies of the 15-85 that I tested, including my own, produce very blurry corners in that case. Worst is at about 24mm, but 15mm is almost as bad. The problem is much less pronounced at distances up to 5m; that's why I did not detect the problem in my chart tests after buying the lens.


Correct focus is critical too. If I simply rely on center focus of my 40d at WA settings, the corners are heavily blurred. I believe that slightly inaccurate focus, decentering, and field curvature add up.


I discarded most if not all of the really bad examples, but will check in my Trash as soon as I am at the right computer again.