Basic rules to avoid 3D eyestrain

http://www.today3d.com/2010/08/basic-rules-to-avoid-3d-eyestrain.html

 

3D is an ever-evolving process, which is why the effect can be such a hit-and-miss affair. But those who insist 3D glasses give them headaches are a little wide of the mark. They are right when using low cost disposable glasses, or dirty glasses, but assuming one is using high quality 3D system with high-end 3D glasses- they are wrong.

It’s not the technology’s fault, it’s really the content that can cause these problems. The more care taken when making the content, the better off everyone’s going to be. It’s easy to make 3D but it’s hard to make it good – not going to cause eyestrain. There are several common mistakes that can cause discomfort, and easy ways for that to be reduced, yet they’re only just being learned and put into regular use.

 

Interaxial distance

The interaxial, or the distance between the two cameras, controls the overall depth of the 3D effect. Objects will appear closer or further away but they won’t change in size, so it’s important not to increase the interaxial distance too much.

 

Hold the shot together

By using the people or the ground plane, or some continuous sense of depth in the shot, it holds the shot together. One of the complaints people sometimes have about 3D is that it feels like a cardboard cutout: that there’s a cardboard cutout, then some space and then another cardboard cutout. By using a careful choice of interaxial spacing, and also by having something in the frame like the ground plane, or smoke or atmosphere or something, then you can start to hold the shot together.

 

Convergence

Our eyes converge inward as we look at an object moving towards us. In 3D it’s essentially the same thing: we converge the angle of the left and right cameras, and this alters the particular 3D plane to which our focus is drawn. Objects in front of the convergence point appear to be coming out at us, while objects behind do the opposite. Care needs to be taken, however, particularly when fast cutting is used.

 

Vergence-accommodation conflict

Every time we cut to a new shot, the subject of interest is at a slightly different distance from us. On every single cut, your eyes are making an adjustment to depth – you’re trying to find that object. It’s a very subtle distance, it’s not a great distance, but that’s what you’re feeling in your eye muscles as you’re trying to work to catch up with the shot. The way we make it much easier to look at is by using convergence in post-production. In that same sequence you adjust the convergence in post production to balance the depth between the shots or even within the shot. Now your eyes are making the adjustment once in the very first shot, and from that point on they don’t have to adjust again. It’s very subtle but if you don’t do it, it’s the difference between a comfortable experience and a splitting headache after 90 minutes.

 

Converge in post production!

What filmmakers are now learning is that trying to control the convergence during filmmaking is a waste of time. As cuts are made and scenes are shifted around, it’s difficult to know exactly what shot will follow another, so trying to predict it all is expensive and useless. It’s far better to find the comfort zone of convergence during shooting, then adjust it in post-production once the edit is finished – that ultimately makes the difference between good and bad 3D.

 

Divergence

The opposite of convergence is divergence, and just as our eyes can only converge to a certain point before we go cross-eyed, so they can only diverge to parallel. Overuse of divergence can cause big problems.Typically, when we look at an object in the world our eyes are either parallel if it’s at distance, or they’re converged inwards for objects that are closer. There’s a condition that can be created unintentionally where your eyes are forced to rotate outward in order to fuse this image. When shooting 3D while not assuming the size of the cinema screen the left and right views of the figure can be several feet apart and our our eyes will try to divergence . You might make a great adjustment when filming so it looks great on a 3D monitor, but when you scale it up to a cinema screen it hurts like heck. Experienced stereographers will be able to avoid it, but some low-budget 3D films have been filled with divergence, as they’ve made the cardinal mistake of falling in love with the image on a video monitor when it was really intended for a cinema display.

 

The Brain Part...

With all the respect to our eyes and to optics, about 50% of depth perception is done in our brain regardless of the stereoscopic information. Humans get vivid depth cues from focusing the eyes and not only by the difference between the images from each. Filmmakers know this and merging this part of 3D vision with stereoscopic shooting is not easy to do. For example, our eyes wants to change focus from near to far in order to change priority according to the 3D movie, but in the same time our brain that have learned that a movie is ‘flat’ and that basketball is round do not want change focus. We reflexively try to refocus and that gives us eyestrain. another example is that we rely on moving parallax to gauge where things are. When you move your head, things change relative position. 3D movies don’t do this – so it throws off our sense of where things are. So, you either keep perfectly still, or you can get a kind of motion sickness from watching a 3D movie. None of these can be fixed by creative movie editing. it requires us to learn how to watch 3D. You will not find many kids complaining about 3D eyestrain. There are few reasons for that, but the most important one is that they grow up into 3D and they do not need to learn how to watch it.

 

Basic rules to avoid eyestrain :

1. High Quality 3D systems - Active shutter glasses in the cinema or at home; Massive projector with bright light in the cinema or fast TV (like DLP or Plasma) at home.

2. Clean glasses - own your own glasses, or bring a glasses wipe with you.

3. Seat location - Center seat (especially in USA cinemas that use old polarized glasses with silver screen); Seat far from the screen if you are sensitive to 3D eyestrain.

4. Exam your eyes - continues eyestrain typically indicates minor eye problem that you are not aware of.

3. Above all - Watch ONLY Good 3D Movies.