Focus: Aperture. My Take On The "Exposure Triangle" Part I

Focus: My Take On The "Exposure Triangle" Part I


I cracked and decided to write posts on aperture, shutter speed and ISO.  I finished the reviews of my gear so I decided to move on and try to pass on more knowledge.  I am not an expert on exposure but I will share what I know.


First I will start with aperture however it is hard for me to explain these components separately since sometimes they are link together at times.  So aperture is the diameter of the lens diaphragm that is responsible for controlling how much enters to the film/sensor.  My best way to explain it is, the aperture of the lens is like the pupil of an eye.  So in low light or dark situations, the aperture can to be opened up to allow more light to enter just like a pupil dilates to allow more light to enter the eye.  And vice versa, in bright situations, the aperture closes to decrease the amount of light so the photo is not blown out.  The pupil also constricts in bright situations so you don't burn your eyes.  Aperture allows the photographer to control how much light the lens lets in which can brighten or darken the whole photo.


So now it gets a tad bit confusing.  Sorry, there is no way around it.  The lens, not the camera, is responsible for the aperture.  The camera can control the aperture of the lens but it is the lens that dictates the range of apertures available to you.  So on a lens, the aperture value is denoted by the f-value.  So the value is written as "f/__."  So for example, my 50mm has an aperture value of f/1.4.  So now the confusing part.  The smaller the f-value number, the larger the diameter of the diaphragm.  So f/1.4 can open up larger than a f/2.8, and an aperture of f/2.8 can open up wider than a f/4 etc.  I will go into aperture values and what is good at the end but first I will cover what these numbers are used for and how aperture affects photos.


The f-stops are in numerical values so that you can determine how much you are increasing or decreasing the light by.  So one stop of light difference, is if you go from f/2.8 to f/4.  So what that means is if I change my aperture from f/4 to f/2.8, I am letting in twice as much light through my lens.  It is just math and calculations on figuring out the numbers and how many whole/half/third of a stop difference there is between values.  I wont go into the math of it cause I find it boring and I never think of that in my head ever while I am taking photos.  To get by and use your aperture of your lens(es) well, you just need to understand how it works and the smaller the number, the large the diameter and vice versa.  It is go to know the approximate differences of the apertures so you roughly know how much more light you are letting in or keeping out.  However I have never taken a photo and said "man, I need to triple the amount of light being let in.  I need to change my aperture from f/2.8 to f/8."  I just know "okay, my photo is dark (or underexposed) so I need to let in more light so that means I have to increase the diameter of my lens," and therefore go to a lower f-value to achieve that.  And the opposite to a photo that is too bright where I have parts of the photo blown out or over exposed.


Now, I think it is important to briefly go over what other effects aperture has on photos other than just increasing and decreasing light.  The aperture selected also dictates the amount of area in the photo that is in focus which is called Depth of Field (DoF).  So, what on Earth does that mean?  Good question.  The Depth of Field or DoF is the width of the area of focus in the photo.  So I will use my photos to explain.  A small DoF would have a very little amount of the photo in focus.  Here is a portrait I took that has a very small or shallow DoF:

Portrait - 50mm f/1.4 D

So as you can see, the background is out of focus, her shoulder is not really in focus but just a thin sliver of the photo is sharp/in focus, which is in the same plane as the eye closest to the camera.  You can also tell this by looking at the hair laying on the front side of her shoulder.  If you look carefully, the hair goes from in focus to out of focus very quickly because the DoF, or the width of the area in focus is very small.  This time, the numbers line up... the smaller the aperture, the smaller the DoF.  So that shot above was shot at f/1.4, so the DoF was extremely small.  This is good for portraits for multiple reasons but one of them being is that you are focusing on the model and not any of the trees or the road in the background.  Also most of the face is out of focus which makes the skin look nicer and just makes portraits overall more flattering. 

While a small aperture value has a small DoF, a large aperture has a large DoF.  Example:

Cape Forchu, NS - 17-55mm

This photo was shot at f/11 which has a large DoF which is more suited for landscape photography because you want to have everything you can in the photo in focus.  The photo has the foreground of rocks that are in focus, to the lighthouse in the background.  If this was shot at f/2.8 which is the largest diameter the 17-55mm can go to, the foreground would be fuzzy if I focused on the lighthouse.  That isn't really wanted for landscape photography.  Well, I sure didn't desire it in this photo.  For myself personally I try to have my landscapes all in focus because I want my landscapes to look exactly like it was when I saw them.

Different aperture values have different uses.  Sometimes you have to use a wide open aperture (the smallest number your lens can do) to let in the most light if it is in a dark room for instance.  Sometimes on a bright sunny day you have to close your diaphragm right down so your photo doesn't look like you are being summoned to heaven (completely white everywhere or blown out).  The larger the minimum aperture, the more versatile the lens is because you have the option to gather a lot of light if you need to.  However which a larger diameter diaphragm, comes a larger diameter glass and larger pieces of glass makes a larger price tag.  

Lenses and apertures.  Kit lenses usually have a variable aperture.  This means the aperture has a range depending on the focal length of the lens.  My kit lens was the AF-S DX NIKKOR 18-105mm f/3.5-5.6G ED VR.  Important part of the name for this post's purpose is 18-105mm f/3.5-5.6.  So at 18mm, so the widest angle of view, the lens could have an aperture of f/3.5 and up.  At 105mm, the lens could have an aperture of f/5.6 and up.  This means, as you zoom out from 18mm to 105mm, the lens needs to have a smaller diaphragm to make the optics work.  So as you zoom out, you lose some ability to let in as much light.  This for a lot of normal scenarios is manageable, however there are some cases where you do not want your aperture to change on you if you zoom.  So fixed aperture lenses are in my opinion and I believe almost everyone else's, are best.  Currently I have all fixed aperture lenses which means I can keep my lens at whatever aperture I want and zoom in or out and have it stay at the value I picked.  For an example I will use my example from the portrait above to help pull some of this together hopefully.  I wanted a shallow DoF in that portrait, so I set my lens to f/1.4, the widest the diaphragm in that lens can go.  If it was a zoom lens, and I decided to zoom in, and the aperture would changed then I would have a completely different look than the one I wanted.  More of the photo would be in focus which may not be flattering, and more of the background would be in focus which would make it more distracting.  Another example would be in a dark room which was actually the reason I bought a 50mm f/1.8 D.  I was at a dinner and didn't want to use a flash because it is a little obnoxious to do in a restaurant.  My kit lens couldn't let in enough light so all my photos were blurry and the colours were off because the shutter was open too long.  So that is another occasion to "need" a larger aperture or fixed aperture.  

Smaller apertures allow for the backgrounds of photos to be more out of focus which makes them less distracting and allows for some photos to just look better.  This is called "bokeh" which people pronounce as "bo-kay" or "bo-kah."  I don't know what is the right way to say since people say it differently.  I will cover that in another post since this one is already long enough.  So stay posted for my take on bokeh later.

So to sum up a little:

Aperture is the size of the diaphragm of the lens which dictates the amount of light that is let in as well as the DoF.  Which is like the pupil of an eye dilating and constricting depending on the light conditions.  And the Dof (Depth of Field) is the amount of area of the photo that is in focus which is controlled by the aperture.  The aperture is donated as f-values like f/2.8 which is fairly large diameter to f/16 or f/22 which is a very small hole.  So the smaller the number, the larger the diameter and vice versa.  Then for DoF, it is the smaller the f-value, the smaller the DoF and vice versa.  Fixed apertures that are small numbers usually are best because they can allow you to let a lot of light in compared to larger apertures.  Variable aperture lenses that have a variable range depending on the focal length of the zoom range make it more difficult to harness the light needed for photos sometimes especially indoors.  

The larger the aperture, the more light that you have access to which allows you to have a faster shutter speed.  I managed to keep shutter speed mostly separate from aperture which is nice because it makes it simpler that way but shutter speed will be the topic of Part II.

I hope that is simple and easy to understand.  Personally when I was getting a handle on all of these things I read multiple articles on the same topic so that I could build a strong understanding of it.  Also I went out and practiced shooting a lot which helps to have the "hands on" part of learning as well.  So if some of this is confusing or written poorly I am sorry but ask any of your questions in the comment section or read other sites on aperture and things will hopefully become clearer.  And don't forget to try it for yourself!

Here is a link to a video I made for my Youtube Channel on this topic.