As part of our Photography Basics series we talked about Exposure already and this time we are going to cover the mystery of aperture. Aperture is probably the least understood setting of everything on your camera. While shutter settings are very easy to understand, to long of a shutter speed and you will get blurring, pretty simple stuff. Same with ISO, too high of ISO and you introduce digital noise. But learning how to use aperture properly can kill brain cells faster than a frat house kegger party.
What is this aperture thingy anyway?
Inside each lens is a diaphragm that can open and close, the size of the opening at any given setting is what we refer to as the aperture setting. On our cameras we refer to specific size settings as f-stops such as f/2.8, f/5.6, f/11, etc. While the obvious value of adjusting the aperture is to control how much light enters the camera, there is a secret hidden world beneath the hood that we will need to get a grasp of as well, but let’s start at the basics first.
For a given ISO setting and shutter speed we can adjust the amount of light entering the camera by adjusting the aperture, a smaller diameter (higher f-stop value) will allow less light in, while a larger aperture (smaller f-stop number) will allow more light it. If we refer to the Sunny 16 rule, we know that on a bright sunny day, if we are using ISO 200 and a shutter speed of 1/200th then we will get a good exposure at f/16. As the sun goes down and there is less light, we need to allow more light into the camera, we can do this by opening the aperture up (again, using a smaller number) to allow more light in. This sounds easy enough right?
If that is all there is to it, then this whole aperture thingy would be a piece of cake and life would be good. It is enough to get you going into how aperture plays a role in getting a good exposure, so it is certainly a lesson worth learning and understanding well.
Have you collimated your rays lately?
The opening of the diaphragm also will control cone angle of light coming into the camera and this is why adjusting the aperture can affect the depth of field. To see how this works use your thumb and pointer finger to make a big circle, with one eye closed look through that at a finger on your other hand held about 12″ away. This is going to simulate a large aperture, you will be able to focus on the finger but you will have far less focus on something across the room. Next, make the circle very small and look through it again (now simulating a small aperture), you will be able to focus on both your finger and something across the room equally well. The reason for this has to do with the angle of light coming into your eye, with the large circle, light is able to come in very straight which creates a shorter focal plane, with a smaller aperture opening the light comes in as a cone shape giving a longer focal plane. While this simple experiment has a very subtle effect (not everyone may even notice it working) in your camera it can have a dramatic effect on how your images look.
Factors that determine depth of field
In a comment from an earlier post, Photo Larry provided this very simple guide:
- Distance from the subject (Close=shallow, Far=Deep)
- Focal Length (Short=Deep, Long=Shallow)
- Aperture (Small=Deep, Open=Shallow)
We have already covered this one, the larger the opening (smaller f-stop number) the shorter the depth of field will be.
The longer the focal length the shorter the depth of field will be. This is why you will get more blurring effect on telephoto lenses than you will with wide angle lenses. The most popular portrait lens is the 70-200 f /2.8 because as you back up from the subject and use the longer focal length with a large aperture the more the background will get blurred out.
Distance to Subject
The further you are away from the subject, the more depth of field you will have as well. This is much easier to see with a long telephoto lens, if you focus on something very close to you, much of the background will be blurry, as you focus on things further away less of the foreground and background will be blurry.
Two images with different aperture settings
Hopefully this will help you understand the basics of what your aperture setting can do for you and how to begin to use it to your advantage both in getting enough light into your camera and by being able to add some extra flair to your images using the depth of field.