Hey, Vsauce. Michael here.
This
is called the dolly zoom effect
and the optics that make it possible
are also responsible for what's called the moon
terminator illusion.
A terminator is the line between an illuminated
and dark side.
Light arrives
perpendicular to the terminator but it
doesn't always
appear to.
Maybe you've noticed this before. When the Moon
and the Sun are up at the same time,
and a good distance apart
in the sky, the direction the Moon is being lit
from won't always appear to line up
with the position of the Sun.
What's going on here?
The answer lies
in visual angles.
The further away from you something is,
the smaller it will appear to be.
In psychophysical terms, its visual angle
shrinks - the angle within your field of
view that it stretches across.
Now, this means that everything
we look at is foreshortened,
that is it diminishes incise towards the horizon line.
A line infinitely far away.
Things that far away
are foreshortened to the point at which
they have no height
whatsoever.
This distortion
affects everything that we look at.
But it doesn't confuse us, because
our brains know about it.
We can look at an object that is foreshortened and
figure out what it probably actually looks like.
For example, a door is a rectangle,
but it's wrecked by foreshortening when
opened.
Closer distances appear larger. The whole shape
is different, but your brain isn't
freaked out every time a door opens,
because it understands
that different sensations don't necessarily mean
different actual things.
It's called subjective
constancy.
Our brains cleverly factor in previous
experience and perspective clues from
the surrounding world
to calculate in real time whether changes
in what we sense are because of actual changes
in the things we're looking at or are
just merely products of their positions
or the surroundings.
For example, I, right now on this video screen,
am vulnerable to foreshortening.
But I probably look
okay to you.
However, if we frame in really closely
and remove surrounding perspective clues,
I can be made to look
weird, strange, a little scary,
distended.
I'm foreshortened without the necessary tools
around me for you to mentally adjust.
This
is probably the crux of the Moon terminator
illusion.
Take a look at this.
The line where that wall meets the ceiling
is a straight line.
Seriously, take a look.
If you look to the left and right,
it continues to look straight
and trust me, this building was built with level straight
ceilings.
But that's not what your eye
senses.
A camera will help
demonstrate this. It doesn't add in the
post sensation processing that our
brains do
and we can also frame in to remove other
clues telling us what to think.
Now, sure enough, right in front of us the line is
level with the screen of the camera -
it's a straight line - but
if we move our eyes across the line,
look what happens. If I pan this way,
the slope changes and now the line
appears to be going
up and to the left.
And if I panned
this way, the line appears to be moving
up and to the right.
What's going on here?
A straight line can't have changing slope,
that's what a curved line does.
Just like the curve we think we see
between the Sun
and the Moon.
But wait. If
the line between the Sun and the Moon is
curved because of foreshortening,
why don't we see lines like this one as curves?
Well,
here's a clue.
Clues.
We know what rooms are supposed to look like.
We know how they're built. We have
experience with them and there are other
things in the environment
helping us. But when you look at the sky,
there's not much to help you.
In the absence of clues about distance
and perspective, our brains assume that
whatever we're looking at is
equidistant from us, making the sky a sort of
dome surface, like a planetarium screen.
The only clue we have then is the horizon,
but it's a red herring,
because the horizon doesn't foreshorten.
It's just a place where
due to foreshortening everything becomes infinitely flat.
Brian Rogers and Olga Naumenko 
demonstrated that these things result
in the terminator illusion by using a planetarium.
They projected two dots onto its dome,
mimicking our perception of the Sun
and the Moon. They've then asked
participants to place a third dot on the
straight line connecting them.
But just as in the Moon terminator illusion, people
incorrectly placed the third dot.
They were influenced by a desire to stay
parallel to the horizon,
as if it was subject to the same foreshortening rules.
Our brains also
often fail to factor in foreshortening
when it comes to crepuscular rays,
light beams streaming through gaps in clouds.
They appear to converge from a common point,
as if the Sun is only
a few thousand meters above Earth, but, of
course, in fact, the Sun is extremely
far away
and these lines are actually pretty much exactly parallel.
It's true. They look like they converge
for the same reason railroad tracks
appear to converge.
The visual angle of the distance separating them
shrinks the further down you look.
Sometimes
our brains do the opposite.
They assume
and consider foreshortening even when it isn't
really there, like in this illusion, where
the cars seem to be different sizes but
in actuality on the page
are all the same size. Everything else in
the image is affected by foreshortening,
so our brains assume that the cars
are too and decide that in order for them
all to have the same visual angle, which they do,
the more distant ones must be literally larger
in real life.
The rate at which the visual angle
of something you are looking at changes as
you move toward it, or away from it,
is not constant.
In order to cut the visual
angle of an object in half, its distance from you
must double.
That means objects
really really far away require a lot
more movement to have their visual angle
changed compared to nearer objects.
This is called parallax and it's a major reason
moving allows us to learn so much about
depth.
It's why stuff on the side of the road
whizzes is by you as you drive past,
while distant features of the landscape
appear to only crawl past.
A really distant thing, like,
say, the Moon, 384,000 kilometers away
appears to move so little as you do, it can seem
to be following you.
It's not, of course. It's just geometry.
For the same reasons,
moving a camera through space will
affect the visual angle of nearer
things,
like the Vsauce mug here much more dramatically than
distant things,
like Jake Chudnow's album against the wall.
It is barely changing size as we move back
and forth.
But unlike moving, zooming
increases the visual angle of
everything equally,
regardless of depth.
Notice that when zooming,
the distant album grows and shrinks
right along with the mug. Now, if you move
IN while zooming OUT, or vice versa,
the zoom will be most apparent when looking at distant
things, while the move more apparent on near things.
The result can be trippy.
Here I've been placed where both
effects cancel each other out,
so everything around me changes
instead. Another great illusion that
takes advantage of parallax
is the popular star field or hallway illusion.
Cover the middle of the video
and you'll appear to be moving
much faster.
But you if cover the edges, you'll appear to be moving
much slower. All you're doing is altering
the perspective clues your brain
receives
about movement.
The nearer stuff at the edge
changes position faster
than the distance stuff way ahead.
So if you cover the slow distance stuff your brain
only has the faster moving stuff to
judge speed from. But cover the faster
near stuff and the slower stuff becomes the new
near.
Your brain assumes that you've slowed down.
The optics and mathematics behind all of these effects
were understood at least thousands of years ago.
During the Renaissance, artists used that
knowledge to produce
paintings that imitated reality really
well.
I mean, the perspective is quite realistic.
But... the renaissance?
Why did it take so long for us get there?
I mean, look at this pre-Renaissance painting.
What the heck is going on here?
The perspective is all wrong. That's not at
all what such a scene would actually
look like.
Artists and viewers contemporary to works like that
saw the world just like we do, they
saw foreshortening - they couldn't help but
see it. Foreshortening is right there in
plain sight.
No, foreshortening is
plain sight.
So, what gives?
Were medieval artists all just a bunch of five year olds?
No.
No in the sense that the question is wrong.
Realistic-looking perspective was used
way before the Renaissance.
Now, it might not have always been
mathematically formal perspective,
but foreshortening was understood.
Western art went from this
to this, not because humans all of a
sudden became smarter,
but because of a difference in desire.
What to us today might look unrealistic and thus
bad, was, in its time,
deliberate and popular.
The shift
to imitating the world mathematically,
as if seen through a window,
was more about cultural interests and objectivity and
the individual than it was about artists
all of a sudden becoming
smarter.
Furthermore, perspective illusions shows that what we
think we see isn't always what we're seeing.
A child's drawing may seem crude
in terms of objective mathematical imitation,
but there are other things about the world and
our experience of it worth imitating.
Teasing out
the less plainly obvious to show
something personal
is sometimes even harder than following
perspective grids
Picasso put it this way it: "It took me four years
to learn to paint like Rafael,
but a lifetime to learn to paint
like a child."
And as always,
thanks for watching.
