Back in the old days, when digital cameras were not that popular, films could make learning photography really expensive and complex. Although people know exposure triangle, they usually needed a light meter to avoid exposure mistakes.
Nowadays, thanks to the latest digital format, photography is much less expensive. Almost everyone has a camera, some of them may even have a few cameras.
Even though we live with the latest technologies, the basic principle in photography called Exposure Triangle, never changes.
The Exposure Triangle
In digital photography, when the shutter is open, light travels through the lens and hits the sensor of the camera.
There are three elements to control how much light is being captured.
Aperture, shutter speed and ISO sensitivity.
Aperture can be understood by how big the hole is that allows light to enter the camera. A bigger hole allows more light to enter; in other words, a wider aperture.
Aperture is measured by the f-number, or f-stop. Each f-stop represents one stop of exposure value (1EV). The f-number is a ratio between focal length and aperture size. After some fancy ratio calculations, you will learn that the smaller f-number is a wider aperture and the larger f-number is a smaller aperture.
Aperture also controls the depth of field (DOF). Depth of field is the distance between the nearest and farthest objects in a photo, showing the subject still in focus. With physics, which you can learn more about here, wider aperture gives shallower DOF, appearing as a blurry foreground and background.
When you open the shutter, light goes into the camera until the shutter is closed. This duration is called the shutter speed. It is measured in the unit of seconds.
The longer you expose, the more light you get; in other words, a brighter image. If you are shooting something in motion, a relative slow shutter speed may cause a blurry image. Slow shutter speed may also result in the phenomenon of hand-shaking if you are hand holding the camera.
Fast and slow are comparative. From the above comparison, you can see that even in 1/800 second, there is still motion blur on the fan blades. In 1/200 second, you can’t see any blades. However, if you are taking a picture of a landscape, 1/200 second is giving you a very sharp image.
Hand-shaking may sometimes bring you blurry images especially if you are shooting in long focal lengths. You can use a simple formula to calculate the safety shutter speed. Here is that formula below:
Safety Shutter Speed = 1 / Focal Length
Simply said, the shutter speed that’s faster than 1/50 second, such as 1/100 sec or 1/200 sec, will not cause you a hand-shaking problem if you are shooting at 50mm. The safety shutter speed can be improved by practicing and by the vibration reduction function on higher class lenses.
The third element to control exposure is the ISO sensitivity. This is about how sensitive the camera sensor is to light. When you increase the ISO, the image sensor is more sensitive. In other words, less light will give enough brightness.
In order to bump up the sensitivity, you are sacrificing image quality. You are getting more noise in high ISO. However, high end camera models, such as Nikon D4 and Canon 1Dx, are giving you extremely low levels of noise in high ISO. (That’s why their price is so high!)
This infographic from FilmMakerIQ illustrate the exposure triangle nicely.