F-Stop and Aperture
How was your week? Good? Any good stories to tell? Please,
do tell! Post them below.
So for the next two sessions, I want to go over two of the
most important factors that have ever been presented to the photography
industry. F-stop (Aperture) and Shutter speed. These are the bread and butter
that dictate the kind of image that you are going to get! Knowing how to
operate these factors efficiently can be the difference between “a” shot and
“THE” shot. They work hand in hand, much like a marriage, to produce the
product. A+B=C. You can’t have one without the other. No I may end up diving
into some mathematical terms during my talk on these subjects. So first, a math
joke…
Now on to Aperture!
An image is created through light. Light illuminates
everything around us. Without light, we would not be able to see all of the
beauty that God has blessed this world with. Photography is our way of
capturing that beauty. But this would be impossible without light. One of the
best ways to start off describing aperture to by comparing it to an eye. Think
of your pupil. Think about how you squint when it is bright out. If you are
reading this with someone, go in a room and turn out the lights while looking
at each other. Wait 5 seconds, then turn them back on while watching the
other’s pupils. Did you see how they adjusted?
Aperture works the same way. In terms of photography,
aperture is the mechanism that determines how much light to let in when
exposing a photograph. One of the things to get used to is the fact that a lot
of the factors of photography are inversely related. Aperture definitely
follows suit to that. The more light the aperture lets in, the lower the
f-stop. Inversely, the less light the aperture lets in, the higher the f-stop.
Think of Aperture as a hole. The smaller the hole, the less amount of light is
let in. when would you not want a lot of light to pass through your camera?
Think logically. When there is too much of it. Think about when you flip that
light switch back on. What happened to your pupil size? It shrank.
In terms of aperture numbers, when the hole is smaller, the
number is bigger. Again, think inversely. When we want more light in, the hole
gets bigger, the aperture number gets smaller. In relation to the shutter
speed, the more light that is let in, the faster the shutter speed has to be.
The less amount of light that is let in, the slower the shutter speed has to
be. If you have a low F-Stop like 2.8, then you are going to want a fast
shutter speed such as 1/250. When you have a larger F-Stop such as 22, you are
going to want a much slower shutter speed such as 1/30. But we will focus more
on shutter speed next time. For now back to aperture.
Ok! Welcome back. Let’s take a look at the mathematical
equation for aperture.
This equation represents 3 variables. The F-number is
represented by N, f is the focal length, and D is the diameter of the entrance
hole. The vast majority of lenses have the ability to adjust the hole, as seen
in the photo above, by means of a diaphragm. This diaphragm “stops” up or down
to adjust the amount of light that you need per the exposure that you want.
GREAT. Now we that we are up to speed on what a F-stop
actually is, how does this benefit our photos?
I’m glad that you asked that young wonderer.
Have you ever looked at a rock, or a flower really close?
What happens to everything else while you focus on that rock? If goes OUT of
focus correct? This is a phenomena known as Depth-of-Field (DOF), of which
there are two types. Shallow and Deep. DOF refers to the distance of focus in
an image. This focal distance is very useful in separating a subject from its
background or putting everything in focus for more emphasis on environment. The
lower the f number, the more shallow the DOF, inversely, the larger the f
number, the deeper the DOF. Selective focus, or bokeh as its referred to in
film, is a useful tool in story telling through your photography. This can also
be applied to portraiture and macro photography. A deep DOF where everything is
in focus is helpful in things like landscape photography and astrophotography.
Here, let me clear it up a little better through some
pictures.
Notice how everything is in focus. This type of photography
is really helpful when we are looking to have multiple points of interest. We
find this style namely in landscape photography.
Notice how the background is blurred and out of focus. When
used appropriately, bokeh can give us a beautiful effect isolating the focus to
one subject. This is particularly useful when we want our viewer to focus on
just one portion of the picture. Typically, we find this in portraiture. It is
often used to create drama to a scene and give it some life and purpose.
Make sense? Another thing that aperture affects is the
sharpness of the image. Modern lenses are typically most sharp when the
f-number is between f/5.6-f/8. This is definitely something to consider when
shooting. Being a portrait photographer, as well as a cinematic filmmaker, I am
a huge fan of shallow DOF. But that is not without its troubles. It can be
difficult to focus manually the shallower (lower f-number) the focus is, due to
the fact that the focal plane is so small.
So that about wraps it up! Welcome to the wonderful worlds
of Aperture! Next time, we are going to tackle Shutter Speed, so be prepared
for some stop-go motion!
Till next time!
Josh D. Smith
