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So let's look a
little more closely

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at aperture settings,
which in fact is

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a discussion on, really,
what we call depth of field.

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Depth of field is
about what is in focus

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and what is not in
focus in your picture.

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Your aperture
setting on your lens

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sets the size of your aperture.

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Or maybe it's easier to
think of it as a hole.

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The size of that hole determines
how much of your image

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is in focus.

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When you set your lens
to the largest aperture

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that your lens offers, we say
that your lens is wide open.

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And in that wide
open setting is what

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you see in your view finder.

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If you want to see what is in
focus through your viewfinder,

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that is, if you set your
aperture, let's say, at F/32,

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you'll have to press
the 'Preview' button

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to see what will be in focus.

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By pressing the 'Preview',
the aperture will close down

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to your chosen F-Stop, and
you'll see a darkened image

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in your viewfinder.

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It's another reason
why I use the software.

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Remember, in the
software's Live View,

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we see the image with the chosen
aperture on the screen much

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easier than seeing
a darkened image

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and trying to figure
out what's in focus.

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There's no need to
press a 'Preview'

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button when you use software.

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So in our situation, two
eight is the largest aperture

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in this particular 105 lens.

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We call it F-stop
2.8 , or F / 2.8 .

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Notice that the number is
actually written as F over 2.8

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.

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When we set the diaphragm
to those numbers written

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on the lens, the numbers
in fact represent fractions

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and for that reason
F over two eight

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is larger in terms of size of
the aperture than, let's say,

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F over 4.

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And F4 is larger than
five six, and so on.

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This can be a little
confusing, but if you

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think in terms of fractions,
it will make more sense.

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So these are the settings
we'll look at in this exercise.

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You'll see more potential
settings on your lens.

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But for our purposes
here, these should

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be enough to make the
point about focus changes.

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We'll stay with these five.

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Okay now here is the image I
made of our music box at F/4.

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Take a hard look at what is
in focus and what is not.

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Not very much in the foreground
and background, and so we

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say this image has a
narrow depth of field.

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Not a whole lot is in focus.

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Now at 5.6, here
is the image again.

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Let's compare the two.

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We're seeing very
slight changes in focus.

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That's what we're looking for.

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Take a hard look
what's in focus.

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And now we'll go to F/8.

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And comparing F/8 to five
six, little by little,

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more of the image is
coming into focus.

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You should stop the video and
give the two a careful look.

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Notice the turning mechanism
a tad more in focus in F8

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and a tad more as well in the
screws and everything else

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in that object plane.

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We'll go to the
next F-stop, F/11

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and we'll compare to
the previous image, F/8.

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And again, you should stop the
video to make the comparison.

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And just to move
things along a bit,

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we'll just go right to F/32.

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Look at how small
the aperture is.

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And look at how so
much more of the image

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is in focus compared
to the previous.

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Now to drive home the
point even further,

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let's compare F/32 with F/4.

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So you really see a
significant change.

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That's what these
observations are about.

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We're seeing how focus
or depth of field

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changes more and more, get's
into focus, as we close down,

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or stop down the aperture
to the smaller fraction

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settings on your lens.

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But remember, as we
close the aperture

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to smaller settings
like F/32, we also

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decrease the amount of light
we let into the camera.

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We're not getting
the right exposure

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until we compensate by
increasing the amount of time

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the shutter is open.

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For example, when I change from
one second [clicking sound]

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to two seconds
[clicking sound], I'm

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keeping the shutter open
twice as long, allowing

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more light into the camera.

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The longer the shutter
is open, the longer

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we permit the light
to enter the camera

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and to be read by the
sensor, compensating

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for the small aperture setting.