Why 3D does work

The 140 character limit on Twitter does leave me often without enough space to write what I mean, so here’s a blog post.

I read this blog saying that 3D “doesn’t work”: http://blogs.suntimes.com/ebert/2011/01/post_4.html

The gist is that because our eyes focus individually on objects with lenses, even if the stereo separation (by 3d glasses) tells us an object is nearer, our eyes are not evolved to resolve the conflict. I think there is a point to be made here, which is that even though 3d glasses trick our stereo separation cue, they don’t really focus the image where it should be. But I don’t think this means 3D “doesn’t work” it just gives us a headache (which is definitely true from my experience!). The amount of headache we get depends on a few things I reckon, but it probably due to how much our senses disagree, and the amount of re-focusing our eyes have to do.

There was this post defending it: http://cineform.blogspot.com/2011/01/another-overstatement-that-3d-wont-work.html saying that after 15 feet our eye lenses don’t really care, which I agree with.

Then Naty Hoffman posted this: http://twitter.com/renderwonk/statuses/29815065192435713 that TVs are typically closer than 15 feet, so the original point holds.

Addressing the original point, yes there is a discrepancy between stereo separation and individual focus, but if you think about it, our eyes must be able to compensate for this difference, otherwise people with short-sightedness wouldn’t be able to judge depth without their glasses on. Let me conduct a quick experiment: *takes off glasses* – yes I can still perceive depth, of course!

So ’3D will never work’ is clearly untrue. But it could be uncomfortable to watch – I often find that when I am not wearing my glasses my eyes get strained because they are trying to focus on objects which they are unable to focus on. The question is, how uncomfortable will it be?

My gut reaction (without doing any maths) is that it’s a function of the real distance and the fake 3D distance. So for example an object pretending to be at 30 metres but actually at 40 will be more comfortable than an object at 20 metres but actually at 40. But how does this change with a closer screen? Will an object pretending to be at 3 metres but actually at 4 metres have the same comfort as an object pretending to be at 30 metres but actually at 40? My gut reaction is yes, I think it’s the ratio of the fake to real distances which is crucial: the closer it is to 1.0, the more comfortable the effect. So even though a TV is closer, it’s also smaller, the ‘fake’ distances are closer to the screen, and everything scales down, meaning comfort level is similar.

I’ve heard reports that the 3DS is much more comfortable to watch than a cinema or TV, and this would logically hold water. Even though the 3DS is held nearer (lets say 0.40 metres) the objects onscreen aren’t going to poke out much, say 5 cm max (so 0.35 metres). This ratio would be lower than the cinema or TV so possibly more comfortable.

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