- [Instructor] When shooting for stereoscopic 3D,
you're actually recording two images at once.
All of the same rules apply to these images,
except that it's now extremely important
to carefully calibrate the two recordings.
Often, this calibration needs to be perfected
in post-production.
Aside from setting the so-called interaxial distance,
and this was once called the interocular distance,
that is the distance between the two lenses,
there's not much to do on-set
other than making sure the images match focus,
exposure, lens length, and white balance
as much as possible.
They need to be really carefully calibrated to match.
The reason this is so important
relates to the way brains perceive visual information.
Your brain picks one eye to be the hero eye, if you'd like.
That's the eye that's providing
the most important information.
And the other eyes fills in the blanks,
confirms or contradicts what is apparently being seen.
The choice of hero eye can change
from one moment to the next,
unless you have better vision in one eye,
in which case that will tend to be the main eye
you use for seeing.
The processing of image information from your eyes
happens pre-cognitively.
That means you're not aware of it happening consciously.
Consciously, you just see an image
and, I suppose, have opinions about it.
This works fine in real life,
but if the images don't match properly,
your brain struggles to work out
which eye has the real image
and which eye isn't fully telling the truth.
And this can result in headaches, dizziness, and fatigue.
In fact, some people
who need glasses and don't realize it
often suffer from headaches for this reason.
When editing video that was shot stereoscopic,
you might well only edit based on one camera,
choosing your shots as you would with regular 2D video,
and only examining and making choices about the 3D
when you're close to a finished edit.
One major issue with stereoscopic 3D
is that your audience will be in the habit
of being able to choose what they focus their eyes on.
Not so when watching stereoscopic footage,
which has a focal depth
like any other kind of image on a flat plane.
To get around this problem,
filmmakers sometimes create a composite image,
with a 2D in-focus background
and a stereoscopic 3D foreground.
The result is much easier on the eye and the brain.