vimeo.com/.../1213261

Depth-of-field is an obsession for some,

but it's just a repeatedly poorly
explained circle of confusion for most of

us. Between the optical physics and the
algebra,

lies a very simple truth with two
variables that you can control to get more

selective focus with your camcorder.

(techno music opening)

Depth-of-field is simple. It might even
help if you think of it as depth-of-focus,

or selective focus. Having a deep or wide
depth-of-field means everything's in focus

and, you have no selective focus control.

A shallow or narrow depth-of-field means
only your subject is in focus and

therefore, you have a great deal of
selective focus control.

For most of us point-and-shooters, really
deep depth-of-field is nice, because then

we don't have to worry about focus at all.

Everything's in focus.

Fortunately, when the primary factors that
determine the depth-of-field is the

aperture, which is inherently small in a
small camcorder.

Artistic-types and wannabee artistic-types
like more control or keep some stuff in

focus, while leaving other stuff out of
focus.

Deep selective focus is one of those
details that Hollywood has the time, money

and personnel to pay attention to.

And, Hollywood also has big cameras and
big cameras mean big apertures,

with potentially shallow depths-of-field.

This tiny square represents a one-sixth
inch CCD, which is pretty typical for a

consumer camcorder. Although larger
one-third inch and half-inch or even

two-thirds inch sensors are typical of
more expensive models.

35mm film is larger still, Ultra
Panavision 70mm even bigger, and then

there's the gigantic Imax frames.

Larger formats require larger aperture
lenses and have the potential for more

control over selective focus.

The horrible equations that explain all of
the optical physics, start with a

hyper-focal distance, which is the nearest
you can focus and have an infinite

depth-of-field.

The focal length or zoom, is an important
variable.

As is the "f" number aperture.

Now we got to calculate the near limit of
the depth-of-field where another important

variable pops up, the subject distance
from the camera.

Then we calculate the far limit
depth-of-field, subtracting the near limit

from that, substituting the focal distance
equations back in which gives us...

Look! If you really want more selective
focus options, you really only have to

worry about: zoom, aperture, and subject
distance.

And since our control over the aperture is
limited to opening it up,

that leaves just zoom and subject
distance.

As we zoom in on the subject, the
depth-of-field gets shallower and if we

move the camera closer to the subject, we
also get a shallower depth-of-field.

Which leaves us with an interesting
conundrum,

If we zoom in to get a shallower
depth-of-field,

then physically back the camera up to keep
the subject the same size, we get a deeper

depth-of-field. In other words, the two
cancel each other out.

Fortunately, the two variables don't
interact in any sort of simple way,

which is something you can exploit.

I'm standing about 60 feet from the
background right now and about three feet

from the camera. The zoom level is set to
zero.

I'm still standing about 60 feet from
the background right now,

but this time the camera's about 20 feet
away and zoomed in about 10 times.

There are some very good, interesting and
artistic composition, framing and relative

perspective reasons why you might want to
back the camera up and then zoom in.

But if you just want to increase selective
focus control, get your subject away from

your background as much as possible, and
then either zoom in or get your subject as

close as possible in the foreground to the
camera. This may be one reason why you

tend to see flowers in depth-of field
demonstrations all the time.

And if you want to win a foreign film
award,

just remember the words of legendary
producer/director Billy Wilder:

"Make sure you shoot a few scenes out of
focus."

(cymbal music)