Back to Basics: Apertures/F-Stops, Shutter Speeds and ISO's

Image courtesy: Darren Robertson/Free Digital Photos

In this second article of the "Back to Basics" series, the focus is on the very misunderstood concept of            f-stops/apertures, shutter speeds and ISO's, and more importantly, how these three concepts work together to create a desirable exposure.

It is easy for seasoned amateurs and pros, and especially camera salesman, to forget that they once also grappled with how these functions work. This can make asking someone to explain it to you quite a challenge and at times a little intimidating. Let's break it down.

Keep this in mind for now - the decisions you make on how to use these three concepts will change your picture in one way or another, and the key is to use them so that you get the effect you had in your original idea or vision.

What is it and how does it work?

Apertures and F-Stops

Pick up a camera with a lens, a SRL lens or find yourself a picture of the front of a lens and look down the barrel.

The aperture is the hole in the lens that lets light in to pass to the light sensitive object of your camera (film or sensor). This aperture changes in size. Take your thumb and forefinger and make a small circle. When the hole is smaller there is less space for light to come in, so you have less light passing through. Now make a bigger circle. When the hole is bigger there's more space for more light to pass through.

Keep your fingers there. The size of this hole (aperture) is measured using a unit called f-stops.

There is a set list of f-stops in photography which are 1, 1.4, 2.0, 2.8, 4, 5.6, 8, 11, 16, 22 etc.

This part is where alot of people get stumped, because the biggest physical hole (aperture), like the one you are holding up, is explained as the smallest number f-stop. Let me explain...

Make another small circle with your thumb and forefinger and say to yourself, this is F8 aperture. Now make your hole bigger and say to yourself, this is F4 aperture. It's a smaller number but a bigger hole. Memorize this!

Do not focus on these numbers as meaning anything too important (yet). Just note that the bigger the hole, the more light comes through, the smaller the number. There are different ways to memorize this. Use some of the following sayings; "Small numbers are a BIG deal", "Dynamite comes in small packages" or make up your own.

Another slightly confusing concept is that going from one f-stop (hole size) to the next, will either double or half the amount of light that enters your camera. Hold your fingers up again making a small hole and say to yourself, this is F8. Make your hole (aperture) bigger and say, this is F4. F4 has now let in double the amount of light than F8 would have.

You are probably wondering where these f-stop numbers come from and why anyone would decide to use a smaller number f-stop for a physically bigger hole.

Well, simply, the f-stop number, like F2, is actually the bottom half of an equation. 

So if you choose to use an F2 aperture, which as you now know is a physically bigger hole and lets in more light, you are actually using a hole that has a diameter that is 1/2 the size than the length of the lens.

So if your lens is 50mm then the diameter of your aperture will be 25mm. If your lens is 100mm then you're aperture will be 50mm.

If you're using F8, you're using a hole that is smaller and lets in less light because it is only 1/8th the size of the length of the lens.

So if your lens is 50mm then the diameter of your aperture will be 6.3mm. If your lens is 100mm then you're aperture will be 12.6mm.

As you can see the final estimation is that the F8 aperture diameter equation is in essence, much smaller than the F2.

Shutter Speeds

Shutter speeds are much easier to understand than f-stops (thank goodness).

The shutters in the camera are those pieces that look like leaves, that cross to open and close. Image courtesy Scarlet-Rain

The shutter speed is the speed at which these leaves stay open and then close. Shutter speeds are measured in second increments and fractions of second. These are generally: 1/1000, 1/500, 1/250,1/125,1/60, 1/30, 1/15, 1/8,1/4,1/2,1 sec, 2 sec, 3 sec, 4 sec and so forth.

Imagine in your mind that you decide you want to have the shutter open for a longer period of time. You would therefore use a longer shutter speed such as 1 second or 2 seconds or perhaps 3 seconds.

In order to hand hold a camera, most people have to shoot at at least 1/60th of a second. If your shutter speed is slower than that, using a tripod is highly recommended.

Shutter speed also relates to any movement, if any, going on in your scene. If there is movement and you want to freeze it, then a faster shutter speed is needed. If you have movement and you want to capture the movement and create the slight movement blur effect, then a slower shutter is needed.

ISO's

ISO stands for the International Organization for Standardization and quite simply, it is the sensitivity that film or a censor has to light. The crystal grains on the film or sensor vary in size. The bigger crystals grab more light than the smaller ones in the same amount of time. So it's not really about how long smaller and larger crystals take to grab light, but rather how much light they grab in the same amount of time. This is referred to as "Film or Sensor speed".

ISO is measured in set numbers ranging from 50, 100, 200, 400, 800, 1600, 3200 and so forth. Based on the explanation above 3200 speed will have larger crytal grains than 50 ISO.

A good guide to have, is on a sunny day you will more than likely not have to shoot higher than 200 ISO because it is quite bright outside. If you are shooting later afternoon or in a low lit scene you may want to hike up your ISO to 400 or even 800, depending. Keep in mind though that the higher your ISO, the bigger your crystal grains to capture more light quicker, the more grainy your picture will be. That may or may not be part of your plan.
 

Using Them All Together

When deciding what apertures, shutter speeds and ISO's you want to use, ask yourself, "What am I trying to accomplish in my image?"

Look at your scene and answer the following 10 questions: (Think of them in the same order you've read them here)

1) What is my light source?

2) Is the light very bright? (Do I need a smaller aperture like F8 or F16 to let in less light)

3) Is the light more dim? (Do I need a bigger aperture to let in more light, like F2.8 or F4 to let in more light)

4) Is there something in my scene that is moving?

5) If so, do I want to capture the movement or do I want to freeze it? (Do I want a slower shutter speed to capture or a faster one to freeze)

6) Depending on the light I'm using, what ISO should I use? (Should I use a faster ISO because of dim light, or can I use a slower one for bright light)

7) Do I want a grainy image or a non grainy image? (Should I use a faster ISO like 400 for graineness or a slower one like 200 for less grain)

Always remember that for every decision you make regarding aperture, shutterspeed or ISO you are potentially sacrificing something else.

Here are a few combination examples:

- Large apertures will give you more light, which may cause overexposure (too much light) if using very fast ISO's (800) and slow shutter speeds (1/60).

- Small apertures will give you less light, which may cause underexposure (too little light), if using slower ISO's (50) and shutter speeds that are too fast and don't let enough light in (1/1000).

- In a bright sunny day, a large aperture (F2.8 letting in more light), with a faster shutter speed (less light with fast speed of 1/4000), and a slower ISO (100, less grain) will probably give you a good exposure, low grain image.

Keep running through different combinations like this. A very useful chart for all photographers is what is called The Sunny 16 Rule. It's literally a chart that gives you quick access to find correct settings for different variations of apertures, Shutter Speeds and ISO's. Keep it with you always.

Keep in mind that there are NO rules in photography, only guidelines.

Any questions regarding these topics can be emailed to enquiry@shutterfliesphotography.com.

If you've decided that you want to become a serious photographer there are many great colleges and schools in and around the Fort Lauderdale area that offer thorough courses of Photography, such as The Art Institute, Fort Lauderdale, The Art Institute, Miamiand Barry University, Miami Shores

If studying full time is not your thing there are many great online photography options, such as The Academy of Art and Ashworth College.