So this is why 3D movies never take off

We’re in the middle of yet another revival of 3d movies at the moment – and I can’t help thinking they look a bit rubbish as 3d. Just like they did the first time round, over 60 years ago.

A modern colour anaglyph in red-green. Public domain, via Wikimedia Commons.

Back in the 1950s, TV was going to kill the movies stone dead. Yup, movies were history – Neanderthal dinosaurs doomed by the unstoppable power of The Future. Unless, of course, every cinema went to 3D right now, no delay. One of the upshots was that my father, an electronics engineer working for Western Electric (who had the cinema maintenance contracts), ended up being roped in on weekends in 1953 – along with Rudall Heyward, a septugenarian movie-maker who knew about projector technology – to urgently rig cinemas so they could show 3D movies and thus be saved from certain extinction.

At the time there were two techniques for producing 3D. One was red-green anaglyph, in which two slightly different images of the same scene were printed to a single piece of film in red and green. Special glasses with red over one eye and green over the other produced a black-and-white 3D image. The other was full technicolour, but involved ganging two projectors up with a Selsun motor and playing two reels simultaneously, one with an image polarised 90 degrees to the other. The audience wore special glasses that matched the polarisation, meaning that the left eye saw the image of the one projector, and the right eye the image of the other. Voila – 3D.

It was (relatively) easy to convert an everyday cinema to 3D because most already had two projectors so they could swap reels without interrupting the film – the projectionist would rig up the next reel on the non-operating projector, bring it up to speed, and open the port from the projection booth at the right moment.

There were only three problems. First, this was New Zealand and there wasn’t any TV. We didn’t get that until 1960, and then only in the main centres. So the blind panic by the cinema chain wasn’t exactly rational. The second problem was that, at the time, there was only one 3D movie on the New Zealand circuit, a horror flick about waxworks starring Vincent Price.

The final problem was that the 3D experience wasn’t realistic – a point audiences eventually realised, because after an initial burst of wild popularity it faded out again in favour of Neanderthal-level flatness.

Modern ‘wiggle-gram’ version of an old stereoscopic image, showing left and right images in sequence. Note the parallax shift, which is NOT visible when the two are viewed together. Public domain, via Wikimedia Commons.

Has that been fixed today? Not at all – the physics haven’t changed. And the problem’s the same too.

Humans perceive 3D in two main ways. Close up, we see true 3D because each eye has a slightly different angle on the scene. This is what the cinema 3D system replicates, and the principle of using two cameras to do this was known from way back – there are stereo still pictures from the US Civil War, for instance. But that effect, for us, disappears after about a metre or so. After that, we see 3D on the basis of parallax – by the way closer objects move less than more distant ones as we change viewing angle. The brain processes both methods and does a lot of filling in along the way.

This produces several problems when we watch a 3d movie. The first is the same one that old-style stereo slides have – exaggerated 3d of the close-up variety, which occurs because the baseline distance between the cameras taking the shot is greater than the baseline distance between left and right eyes. That produces a stereo depth greater than human eyes are capable of producing – which we can spot. The other is that there’s no parallax movement. The 3D image is identical no matter what angle it’s viewed from – for instance, if you’re on the edge of the auditorium instead of the centre. It’s because what you are actually seeing is two flat pictures, not a true 3D scene with real objects. (Owing to the physics of it, there IS a parallax difference between the left and right images – because they have been taken from slightly different perspectives – but it’s fixed on the plane between them, and you don’t see it when the two images are combined).

A few years back I actually checked out the lack of true parallax shift in 3D movies by sliding my head from side to side while my wife and I were watching a short 3D museum documentary movie on Vesuvius, as if I were some kind of demented sparrow looking for a worm (they pull the trick to triangulate on prey). OK, so I publicly look like a weirdo, but it’s all in the name of science, you realise.

The net result is that, to us, 3D movies have a niggling hyper-real fakeness about them – they have too much depth in one sense and absolutely none in the other. It’s because the system simply doesn’t replicate the way the eye and brain work to produce 3D in the real world – and we notice it, subconsciously. And that, by and large, is why they have never taken off – they’re cool as a novelty – and savvy film-makers were quick to exploit the over-deep stereo vision effect by rigging scenes with immense front-to-back depth, or zooming in on various parts of the leading lady, or something similar. But they don’t exactly present the 3D world as we normally see it.

The other problem with the twin-projector solution, certainly in the 1950s, was that the two projectors had to be precisely in synch. That was why they used Selsun motors – in theory these locked the two machines together. If one film broke (as often happened) the projectionist had to splice the two pieces together with blank film using the exact number of frames that had been lost. All this was to keep the left and right sides of the 3d image in synch. Actually, because the film path through each projector was complex and relied on loops of film, among other things, it always drifted a few frames anyway with the result that audiences often came away with headaches because one eye was watching a slightly different image to the other. The other hazard was eye infections from the glasses, which were recycled without cleaning between sessions, and about as hygienic as a urinal. Ugh.

What do you think of 3D movies?

Copyright © Matthew Wright 2018

4 thoughts on “So this is why 3D movies never take off

    1. I’ve watched both the polaroid and the anamorphic variety. The glasses were still wet from the between-session disinfecting when I last saw a 3D movie (‘The Hobbit, Part 1’), so that’s one step up. Alas, 3D didn’t alleviate the fact that the movie only bore a vague passing resemblance to the book I loved as a kid…

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  1. I like the idea, but admittedly the execution so far leaves something to be desired. Also it might be nice if the film-makers could resist the impulse to have sharp-looking things jump out of the screen at you every five seconds.

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    1. My father used to complain about the 1950s movies doing the same thing – he said they were always trying to make burning beams ‘fall’ on the audience and such like! If only holograms could be made to move and run in full colour, as opposed to whatever light the laser emits. (I find it intriguing that the old Pepper’s Ghost trick is often called ‘holographic’ these days when it’s used on stage… it ain’t.)

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