Do I really want flatness of field?

[sanmich]

Hi all

First, let me start by saying that I am not sure about what I know on the subject.

So these were my thoughts:
the flatness of field is the capacity of a lens to keep items in focus, that are on the same plane then the point of focus in the center of the frame (or am I wrong here?)
This is a great feature IF you want to shoot flat subjects. I can imagine that this is a critical characteristic for a reproduction or an enlarging lens.
Now, in real world, and specially in an RF world, I tend to focus on the subject, then recompose by rotating the camera, not by translating myself regarding the subject. that means that my subject has moved following an arc relative to me, and assuming the "perfect flatness of field lens", my subject is now out of focus!!
If I am right, the perfect lens for that type of action, is the one that has a circular field, keeping the focus even during rotations of the camera.

Ladies and gentlemen, your thoughts, please...🙂

 

[Brian Legge]

Wouldn't your desired 'roundness' depend on the mounted lens? I could see this working with a fixed lens camera but I don't know how it would work if you can change your field of view. In addition, it seems like you'd have to pivot your camera around a very specific point for the film flatness to be the biggest precision loss.

 

[v_roma]

I'll start by stating that I don't know too much about this either so my response should be in keeping with the question 🙂 I could be wrong, but I don't think true flatness of field applies to most situations. I had this question a while back since I often use the focus and recompose technique and Bob Atkins seems to think that, because of the depth of field, recomposing will not be an issue in terms of focus for 99% of the situation. Here is his article.

 

[mfogiel]

Certainly you want flatness of field, if you want to shoot a sharp landscape at infinity.

 

[braver]

You want flatness of field so that everything behaves predictably and your camera is able to tell you what is in focus. If your field is curved, who knows what is in focus? It might accidentally work out if you recompose, but that would almost be a miracle occurrence.

 

[ampguy]

well, your film is not perfectly flat, so a little field curvature in the lens could potentially give your film camera a perfectly flat field by balancing things out here ...