Hi everybody and welcome to another episode of Exploring Photography right here on AdoramaTV
brought to you by
Adorama it's your one stop shop for all your photo needs
check them out Adorama.com well we've been exploring The Exposure Triangle
and today we're going to do something with a little bit technical. There's some math
involved but don't be afraid
and I'll explain everything with some groovy graphics so I will make it crystal clear
AdoramaTV presents
Exploring Photography with Mark Wallace
Now aperture value, remember we talked about the aperture before that's the thing inside
your lens that opens and closes to let in more or less light and also helps us to
control
how much of our image is in focus but one of the things that throws people off a lot
is the numbers, we have numbers like f2.8
f4, f16, well what does that all mean why do we have an
f in front of that and why is it that when we have it something like
f16 it means a small hole and f2.8 means a
large hole seems totally backwards and then there's another
thing that throws photographers off all the time. If they
have a camera like this it has a zoom lens so this is a
a Panasonic FZ1000 - awesome camera
It's got a lens that zooms in and out and one of the things that happens with
zoom lenses as you might set the aperture value to something like
2.8 but then when you zoom and all of a sudden
now it says 4 you didn't change anything and just went from
2.8 to 4 - when you zoom out it goes back to
2.8 so what the heck is going on?
Well I need to explain all in this stuff I'm gonna do that with an
awesome animation. Well let's take a look at this animation and this will make
these aperture values crystal clear now before we get there I forget to
mention one thing
on the front of your lens and sometimes on the there is some information
that tells you about the lens and the aperture so on the front of this lens
has a little thing that says 1:1
4/50 and on the front on this one
it says 1:2.8-4.0
4.0/ 9.1-146.
What the heck
do those things mean? Well the 1:
means that there is a ratio between the lens and the aperture.
That's all you need to know about that and it will makes more sense when we show you the animation.
The other number is the widest aperture value
that that lens can have, so on this one it's a 1.4 aperture value that's as wide
as it can be
and in the / says 50 so it's a 50mm
lens. This is a zoom lens and so it's got several values and it's saying that this is a
2.8 to 4
so the widest aperture value is either 2.8 or 4.
Which I'm going to explain in a second and the slash says this is a 9.1
to 146mm lens in other words it's zooming
from 9.1 to 146mm,
now that is melting my brain and so to make all of these little numbers
crystal-clear
I want to show you this animation so join me as we do some math.
f22 or f2.8 is actually an equation where
f = Focal Length: now to make things simple I'm just making up numbers
the
numbers and I'm using are for fictitious lenses but it'll make things a lot
simpler so back to our animation.
Let's say we have a lens that's 100 millimetres
with an aperture value of 2. That would be written
as f/2. If we replace
f with our focal length: we get 100/2
and the result of this equation is 50.
That means that the opening in our aperture is
15mm wide.
100/2 = 50mm.
Now let's say that our focal length is 200mm.
Our lenses now twice as long now
f2 would = 100 mm. Let's do the math again.
f = 200mm. 200m divided by 2
= 100mm so that tells us that f2
for a 100mm lens is not the same as
f2 for a 200mm lens. The openings
are different sizes. Now let's pretend that we had a zoom lens
that had a
zoom range of 100mm to 200mm.
And lets also pretend that the widest the aperture could
open was 50mm now if the aperture was
all the way open and our lens was zoomed to 100mm
the aperture value would be f2. How do we know that?
Well let's do the math 100/50 = 2
Or we can use the formula that I showed you before.
Focal length divided by 2 = 50
Now what happens if we take this lens and zoom it
to 200mm since the aperture can't open
any wider that means that our aperture value
has changed now lets figure out the math and see what it is.
200mm/50mm = 4
Therefore the
aperture value is now f4.
Now if we bought this this made up lens it would have a label that said
100-200mm/1:2-4
The aperture value does not remain constant
throughout the length of the lens. Now this is very common on consumer lenses
because it costs more to make a zoom lens that has constant aperture values.
Now if we wanted our fictitious lens to have a constant
aperture value that would mean that the aperture would have to get larger
as our lens zoomed. The aperture would have to grow from
50mm wide to 100mm wide
as our lens zoom from 100mm to 200mm.
So let's review. The aperture value is a measurement
the size of the whole that the light passes through in the rear
our lens the aperture relative
to the focal length of the lens. So a small
f number is a large opening. Any large
f number is a small opening. Well congratulations you survived a little
math
and I hope you're better for it now remember that you can see more about the
exposure triangle on aperture values at the Adorama Learning Centre
I just want to mention that this little FZ1000, this Lumix
is a fantastic camera it's not mine and borrowing it from a friend Lex. We are traveling
all over the world together
and she wanted to step up from a point you can do something a little more
robust
And I gotta tell you I have some jealousy about this camera. You can read
reviews & more information
Adorama Learning Center about it but a lot of people have been asking. Hey are you
shooting with this?
I am when I can steal it from Lex and borrow this, it's super lightweight and it's a
perfect travel camera and it's very affordable so
just a little blurb about the Lumix. Well again I want to mention that you can
subscribe to Adorama TV
It's absolutely free and you can see more about the exposure triangle and
all the things that we've been talking about so do that right now just click
the link
and subscribe and thanks again for joining me. I will see you next time.
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