Aperture is something that is widely mis-understood to people who are new to the technical side of photography. This is mainly due to the way stops are measured. Once you know the principle of stops in photography you will be able to get a good understanding of aperture.
What Are Stops?
The use of this word is confusing to people when learning about the technicalities of cameras. It’s a very simple principle though, just imagine this: There is a camera one end of the room and a lamp at the other end. When the camera takes a photo, the light is too bright and the shot is over-exposed. Imagine there is only one shutter speed available of this particular model of camera and the only way to adjust exposure is to adjust the aperture.
When the shot is over-exposed you need to increase the amount of stops. More stops mean there is more in the way of the camera, therefore letting less light through. The aperture circle is made up from blades, which allow the size of the hole to be ajdustable. This means you can adjust the amount of light that comes through. Aperture blades look like this:
As you can see, the circle through the middle is what the camera can see, as you close the circle by adjusting the blades less lights is allowed through to the camera’s sensor. So, when you set the aperture blades to make the circle big, that means you have a large aperture with a low amount of stops for example:
f/2 = big aperture / f/22 = small aperture
So, as you probably already know. In darker situations you want to set the f stop number as low as possible.
Depth Of Field
So, you’re probably thinking “What does aperture have to do with depth of field? He must be a fool!” well, that’s what most people would say, maybe. Aperture is the main variable that affects the depth of field in a photo. Most of the time you will want as much depth of field as possible when taking photos of people. It makes the subject stand out and is a very striking effect.
So, lets say you want to take a picture of an apple. On a stick in the middle of a field and you have a 50mm lens with a maximum aperture of f/1.8. The main problem you will encounter in this situation is there will be too much light most of the time, and to get a good depth of field you need to leave the aperture wide open (f/1.8). That leaves you with no stops to restrict the amount of light going in. This would be a problem but there is other stops available. ISO speed and shutter speed. You will want to keep the ISO speed as low as possible (ISO 100). This leaves you with shutter speed as your only light stop. I will be covering this in another article later on but, you will need to have a fast shutter speed. As it’s a bright sunny day you will probably need to go right up to 1/4000th of a second! This is due to the huge f/1.8 aperture.
Sometimes you will want to stop it down a bit, maybe to around f/2.8 to increase the depth of field. Especially when doing portraits otherwise you may find the subjects nose/eyes in focus but their ears/body out of focus slightly. I will also be covering this in a later article.
To clarify, the way to remember how aperture/stops work is: The smaller the f number the bigger the aperture and the more light will be let through the lens. And, the bigger the f number, the smaller the aperture and,the less the amount of light that will be allowed through the lens.