Shallow d.o.f: our brain needs it

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someday

Well-known member
When discussing with people about the need for a 35mm adapter, we always talk about look, cinematography, history, film. But there is another, more important reason:

Our eyes focus on the infinite only when they watch at the infinite. So a camera with infinite d.o.f. with a person in the foreground could be interpreted by the brain as a camera watching at the background (!!). And would be fatiguing and unnatural.
A 35mm adapter makes the image more logical to our brain.
 
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Not sure I agree with this point because our normal vision have almost infinite DOF. So this would be the "natural" state of how we see things. The explanation that makes the most sense to me was always that short DOF gives the object we focus on a more 3d look, which help make it more "real" because unlike real life, we're confined to a 2-dimensional representation when watching a film.
 
No.
Our eyes have a focal aperture of f/2.25. the retina is 30mm wide. The perfect focus area of the retina is just 2mm wide. The rest is bluried.
Our eye has a shallow DOF and small focus area.

OUR EYES HAVE NO ALMOST INFINITE DOF.
Our eyes scan the world at an amazing rate. They move as fast as 1/50 of a second to look at some detail then stops for as short as 1/20 of a second, that information is sent to the brain and then the eyes scans again for new details. In a second we focus on 50 things. This give us the illusion of infinite dof. But it's just an illusion.

Try to look at a person in front of you and still try to see the details on the background. It's impossible because our eyes produce a stereo image. The background is bluried because the 2 images from the eyes are shifted and out of focus. The result is bokeh

reference
 
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someday said:
This give us the illusion of infinite dof. But it's just an illusion.
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Right, but does it really matter? If we *think* that everything we see is in focus, then that's the way we actually interpret the world visually regardless of how it actually is. I've always view the shallow DOF shot in film as being a very artificial construct since I cannot visually recreate the same effect with my eyes, there is always that illusion that even as I focus on something, everything else is in focus as well. A shot with infinite DOF isn't necessarily inherently wrong to our brain; it's just undesirable because it prevents us from being able to immediately zero in to the point of interest, which we can do with our eyes.
 
Huy, i can't agree with you. But i know that it's a common statement that infinite focus = reality. IMO infinite focus has only sense on panoramic views and large shots.
 
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When 3d projection/filmmaking becomes prevalent having infinite focus will work better. Shallow depth of field will look less natural.
 
You are overlooking something that's as obvious as the eyes on your face...

Human beings are binocular, and the eyes are always converging on a single point in front of you. Anything in front of or behind that point is misaligned and 'doubled'. This is the major element in how human beings perceive depth. Focus is very minor in comparison.

Photography used the minor element of depth perception (focus) to separate the subject from the surroundings. Cinematography evolved from photography and adopted the same convention.

Images that have an unlimited DoF are not fatiguing or unnatural at all, using a shallow DoF is simply used to subtly control the point of interest in the frame. Most Sit-Coms and low budget TV are shot with a very wide DoF, and it doesn't bother anyone. We do expect more of cinema though.

Bob
 
It depends on the image. A person in focus with a background in focus is impossible in the real life. And it's UGLY in cinematography.
 
Huy Vu said:
Right, but does it really matter? If we *think* that everything we see is in focus, then that's the way we actually interpret the world visually regardless of how it actually is..
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That's not true at all. If anything, our metal interpretation is the exact opposite and we actually 'focus' on one thing while so many other things ARE in focus. We *think* that our eyes have shallower DOF than they actually do because we can pay attention to one thing in a whole field of things that are also in focus.

Additionally, the assertion that our eyes have infinite DOF is completely false and easily proven wrong. Close one eye so you aren't confused between what's out of focus and what's doubled due to having two eyes. Now put your hand 5 inches in front of your face. Focus on your hand. What happens to everything in the distance behind your hand? It's out of focus. Not because it's doubled, but because of DOF.
 
We'll, when you turn 40 your eyes cannot focus anymore so your theory goes out the window for us in this age category.
 
someday said:
It depends on the image. A person in focus with a background in focus is impossible in the real life. And it's UGLY in cinematography.
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Everything is in focus in real life at all times..it just depends what our eyes choose to look at.

Going back to 3D......... A 3D film would give the viewer that true-to-real-life choice. Things would go in and out of focus at the viewers choice...not the cinematographers.
 
Weston said:
Everything is in focus in real life at all times..it just depends what our eyes choose to look at.

Going back to 3D......... A 3D film would give the viewer that true-to-real-life choice. Things would go in and out of focus at the viewers choice...not the cinematographers.
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AND THIS IS THE KEY!

When you shoot a person talking you suppose to watch to the person, not the background (unless the story needs it)
And this is the reason because the camera has to focus on the person, because if you want the audience to focus on the person IT'S IMPOSSIBLE BECAUSE THE PERSON AND THE BACKGROUND ARE ON THE SAME SCREEN PLANE!
Only a 3D movie could work at infinite focus because the audience would be able to select and focus what they want.
 
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Weston said:
Everything is in focus in real life at all times..it just depends what our eyes choose to look at.
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That is absolutely not true and easily proven wrong.

Close one eye so you aren't confused between what's out of focus and what's doubled due to having two eyes. Now put your hand 5 inches in front of your face. Focus on your hand. What happens to everything in the distance behind your hand? It's out of focus. Not because it's doubled, not because you've decided to not look at it, but because it's out of focus. Because of DOF.
 
I think that Weston has the truth.

Until we shoot movies in 3D, which could be at infinite focus, the director has to focus artificially on the subject, because the audience can't select the focus on the image projected at infinite, with the result to fatigue the eyes and the brain.
 
someday said:
I think that Weston has the truth.

Until we shoot movies in 3D, which could be at infinite focus, the director has to focus artificially on the subject, because the audience can't select the focus on the image projected at infinite, with the result to fatigue the eyes and the brain.
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That might be true, but all these claims that our eyes naturally have infinite DOF and keep everything in focus at all times are completely 100% incorrect.
 
someday said:
...with the result to fatigue the eyes and the brain.
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I still do not see where you are getting 'Fatigue' from. Many programs pumped out over television have a very wide DoF; don't find them fatigueing*...


Bob

*(With the exception of content, of course)
 
This discussion is pretty ridiculous I think, but being the fool that I am with toomuch time to waste apparently I'm going to chime in.
All this talk about what's in focus for the eye is irrelevant. Our brain is constantly patching together coherent images from tiny fragments as we we scan around the world.
The illusion that we call 3D or depth is a learned construct as is the just the fact that we can make sense of those fragments and patch them together into soemthiong that we imagine to be an "image" of the world in front of us.

People find both low and high DOF images natural and/or unnatural depending on the specific image and their personal experience. How it functions aesthetically would be a more rewarding avenue of thought. But if it helps you aesthetically to think of it as closer to the natural eye - great.

Lenny Levy
 
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