The Circle of Confusion: Exploring Photography with Mark Wallace: AdoramaTV


In this episode I’ll explain the
circle of confusion AdoramaTV presents, Exploring Photography with Mark Wallace. Hi everybody and welcome to another episode of Exploring Photography right here on AdoramaTV, brought to you as
always by Adorama. Adorama is the camera store that is the
absolute best in the world, anything you see in this video you can get at Adorama.com, check
them out and see exactly what the hoopla as all about they are incredible. Well on
today’s episode we’re going to be talking about the circle of confusion and this is sort of a
technical episode and I’m doing this because a lot of
people have written in and said what exactly is the circle of confusion. Well the circle of confusion is a technical term
that helps you understand how our camera focuses light, it helps us
understand depth of field and bokeh, and it’ll also help you
understand why some lenses are so darn expensive because they focus light a
little bit differently than other lenses. Now this is a highly
technical episode and so I have oversimplified a
lot of this stuff so if you know all about circle confusion don’t get angry
that I have oversimplified stuff, but I’m doing this
because I just want you to understand the basics of the circle of confusion. Now to
understand this I’m asking for some help so to help me explain all of this stuff Lex is here to
walk through all of this with me and we’re going to do a
little animation and some walk through’s and all kinds of stuff so you can clearly understand the circle of confusion, and
really to understand that we need to understand how our camera focuses so let’s just for the sake of
argument say that I want to focus my camera on Lex’s face. Lex’s face would be
called the point of focus, now I made that term up so don’t quote me on that, this is the point of focus, I want to focus on her face. Now light is going to travel in a cone
it’s going to go into the lens, its coming into, so from big to small. Now in our lens it’s not actually one lens it’s a
series of lenses and each lens inside of this lens, those are called lens
elements and they do different things that we’ll find out about later but the one
that we care about right now it’s called the focus element and we
focus our camera, that focus element is moving back and
forth and what it’s doing, its changing what’s
called the focus point, so when our light comes in to our lens it comes in through that element and
then it’s focused to a point and that point moves back and
forth depending on our focus, Now what we’re trying to do is
get that focus point to line up with what’s called the plane
of focus, in other words our camera sensor or if you have film your camera’s film, when those
two things line up well your focus point is in focus, in
other words Lex’s face is going to be in focus on our
camera sensor. Now I know that sounds sort of confusing when we do it like this, so to
make that crystal clear I want to show you this animation. Ok let’s
keep this very simple let’s say we have a point source of light
something like a flashlight, a small Christmas light or something similar, a point source of light
is a round light like the sun. Now let’s add our focus element that is a glass inside our lens that
focuses our subject when our point source of light shines it travels through our focus element and is focused to a focal point. When our focal plane and our focal point
meet we have an image that is in focus, when we
focus our lens the focus element moves our focal point. If we take our two-dimensional drawing
and make it three-dimensional, you’ll notice that our
point source of light is focused as a cone when we rotate the cone it
becomes a circle, and that circle becomes smaller the
closer we get to our focal point the circle also becomes larger as we
move past our focal point, notice that our circle
becomes a very small dot at the focal point. Let’s look at our two
dimensional drawing again and let’s zoom in on our focal
point and focal plane, when our focal point and focal plane are
aligned our point source of light will be a
clear point or a dot that’s how we perceive focus, but if the
focal point is off the focal plane by a small amount
will have a dot that’s slightly larger but our eyes will still perceive that as
in focus there is a range just before and after
our focal point that we will always perceive as in focus even though technically it’s
not in focus, that range is called the circle of
confusion, anything the size of that circle or smaller will be perceived as in focus our eyes
can’t really tell the difference between a perfect focus and something that’s just off focus, both
the small and slightly larger dots look pretty
much the same to us. When we use a smaller aperture setting
that changes the convergence of our focus, that makes the range of
the circle of confusion larger and that’s what gives us greater
depth of field, the point of focus is inside the circle
of confusion but things in front and behind it are
also inside the circle of confusion. I think the animation really helped us
understand more clearly about the circle of confusion but to
help understand how the circle of confusion affects bokeh, Lex and I went out last
night and we shot some stuff at night so let’s take a look at that. In this
nighttime scene we have our aperture set to 1.4 and notice how the lights behind Lex are
nice and out-of-focus we have a terrific bokeh. Now when I take my aperture and I
start stopping it down to f/2, f/2.8 down to f/4 f/5.6 we can see that Lex is now
underexposed that’s okay because we’re all really
paying attention to is the background, look at those lights how they become more
of a point source of light, go down to f/8 you can see that
they are really in focus. Now let’s go all the way back to f/1.4 and
you can see that Lex looks terrific but those lights behind
her becomes soft and out-of-focus. Alright well now that we know
all about the circle of confusion ,how light moves in a cone and hits our focal point and so when that hits
our focal plane things are in focus, we have all of that but
why does the circle of confusion tell us why some lenses are more
expensive than others? Well here’s why, in light we
have three primary colors RGB red, green and blue, when red,
green and blue go through our lens elements their traveling at different
wavelengths which means when they hit our focal point they don’t all hit the same focal point one is here,
no one is here and one is here. To get those all to line-up we have to
have several more elements in our lens to
correct all of those colors moving at different wavelengths so that they all line up at
the same place. Now on lower priced lenses you don’t have all those extra elements and so
you’ll have a shift and so blue usually hits the focal plane
a little bit differently than green and red which means we have
something called chromatic aberration when you look closely at things like
tree branches and light poles in kind of line you’ll see a little outline that might meet
blue or might meet magenta and it also means that our photos look a
little bit soft and out-of-focus, and so to correct all of that you have
to add extra elements which means more cost in production which means that the
lens is much more expensive in fact really high
quality lenses will start somewhere at fifteen hundred dollars in go up from there, some of them are two, three
or four thousand dollars and cinema lenses
if you’re shooting video can be in the tens of thousands of
dollars, they are very expensive because of all of that. Well thank you so
much for sticking around and learning all about the circle of confusion thanks Lex for helping us out and
learning how to understand all this stuff, remember you can read more about
all of this stuff at the Adorama Learning Center of course it’s
absolutely free and we would like you to subscribe to
AdoramaTV, again it’s free so just click on the subscribe button and
do that right now, thanks again for joining us and we will see you again next time! Do you want great-looking prints at low-cost? Be sure to visit our easy to
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