Why You Should Understand Exposure
Simply put: a photo is an exposure and the more you understand about exposure, the better your photos will be. Once you start to grasp exactly what aperture, shutter speed and ISO does to a photo, you’ll know how to use them correctly and creatively. This posts covers how to create the right exposure for a situation, as well as the negative consequences of each exposure factor. There are also links to read up in much more detail.
How an Exposure is Produced
There are 3 factors that combine to produce an exposure, and each of these factors carry a potential problem at the same time:
Firstly, the light passes through the aperture which determines how much light comes in.
Secondly, the shutter goes up to allow light onto the sensor/film.
Finally, the ISO determines how much to increase the exposure by.
I’ve written posts on all three of these factors that can be viewed by clicking on them, but here’s some information to give you a basic understanding of what else they do:
The aperture affects the depth of field.
The shutter speed determines whether there’s motion blur or freezing.
ISO produces digital noise/grain and in turn, affects the quality of the image.
All of this combines to produce an exposure like the one below. The aperture is f/2.8 resulting in the shallow depth of field and soft feel to the photo, the shutter speed is 1/100 of a second, meaning that I could take the photo comfortably without motion blue, and the ISO is only 100 which has resulted in very little noise.
Getting the Correct Exposure Using Different Modes
Different modes use this meter to automatically create the correct exposure; when the ‘needle’ is in the centre, the photo will be exposed correctly.
Aperture Priority will hold the needle in the centre (unless you’ve moved it manually) and as the aperture changes to allow more light in, the shutter speed will also change to allow less light in to maintain an even exposure. The shutter priority mode will do the same thing, only the other way round; the shutter speed is changed, the aperture will change accordingly and automatically.
Manual mode allows you to change both aperture and shutter speed at the same time and not conform to a certain point on a light reader. This mode is mostly used by more experienced photographers who want the extra control over a photo and know what settings to use off the top of their heads. The light reader will still move to indicate how exposed a photo will be, helping the photographer.
Different Exposure Conditions
Night: Photos of scenes at night are best taken using a tripod, that way you can create long exposures and play with the light without producing a blur. This photo below was taken using a 30 second exposure, a wide aperture of f/4.5 and an ISO of 400.
indoors: I regularly use a flash indoors and bounce it off a wall or a ceiling to create a more natural effect. The settings used below were 1/50 of a second, f/7.1 and ISO400 with a flash bouncing of the ceiling.
Event: Due to the lighting conditions at an event, and the fact that you’re often not allowed to use a flash, you often have to boost your ISO. Also, artist on stage tend to move around quite fast so you have to use a fast shutter speed as well. This results in a wide aperture with a narrow depth of field, a high ISO, and some pretty cool lighting conditions like the photo below; taken at 1/160, f/2.8 and ISO1600.