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3D cinema and depth-of-field

by Rob Friesel

With 3D turning into a big draw for box office films now1, and with Sony claiming they’ll put in our living rooms by the end of the year, I’ve had a few conversations now about the 3D effects and whether/not they “feel right”.  Most folks seem to agree that if you let go and relax your eyes and just stare straight ahead, that you get used to it pretty quick and that the 3D effects add a little something special to those films.  But most folks also agree that something about it also feels a little bit off, and that it doesn’t take much to pull you right out of that relaxed adjustment.

If you think about it for a minute, you’ll notice that it’s the depth-of-field2 that betrays you.

This came to me relatively early in the film when I went to see Avatar.  It’s a relatively inconsequential scene:  Jake Sully is floating in zero-gee, coming out of the interstellar suspended animation…  The camera is sharply focused on him and the depth-of-field is pretty shallow…  Sully is groggy and floats dead center in the frame…  And down in the lower left of the frame is a box or a cylinder or something with a label on it.  But you can’t make out the writing because it’s in the foreground, too close and out of focus.  But you want to know what it says, so you move your eyes to the object and try to focus…

And that’s it, right there.  Your brain has got competing signals.  You perceive everything in the frame in 3D.  So your brain assumes you can just track the objects with your eyes, move your own focus.  Your brain believes it ought to be able to make out those words.  But the letters never snap into focus.

But now you’ve pulled yourself out of the scene now.  Your eyes aren’t relaxed anymore, they’re not in the center of the frame “where they belong”, and you’re certainly not caught up in the transformative magic of the 3D effects anymore.

So the questions then become…:

  1. How many 3D films are we going to need to see before we train our brains to “turn off” those attempts to change focus? That is to say, is this just an artifact of the fact that we have already “trained” ourselves not to try this change-of-focus with traditional 2D cinematography and we just need to train ourselves to do the same thing with 3D?
  2. How are directors and cinematographers going to change their framing techniques? Seriously, is the focus always going to be in the center of the frame “from now on” when it comes to 3D films?  Because I can tell you it was awkward and maybe a little bit vertigo-inducing to look at the edge of the frame in those 3D shots.
  3. How is this going to work in the living room? Glasses that you can lose?  Or that your cat will chew to bits?  Help me out here…  But I guess having a 3D TV in the den will help us get the training hours under our belts to address #1?
  1. See also: Avatar, Alice in Wonderland, Tron Legacy… []
  2. If you’re unfamiliar with the term, try the Wikipedia primer on depth-of-field; though this image is probably enough to illustrate the definition. []

About Rob Friesel

Software engineer by day, science fiction writer by night. Author of The PhantomJS Cookbook and a short story in Please Do Not Remove. View all posts by Rob Friesel →

2 Responses to 3D cinema and depth-of-field

Dr. Martinus says:

I fully agree to the obversation but would say that directors and cimenatographers are obliged to make use of 3D only by not using the depth of field to imitate kind of a 3D image. Because the human eye doesn’t know a depth of field. It focuses on the spot where you lay your eyes on in an instant. Thus, a 3d screen has to provide the means to do that.

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