Source: https://www.photopills.com/articles/exposure-guide
The correct exposure is a combination of 3 things: aperature, shutter speed and ISO. Hence the diagram above.
But, just to go back a step, what really is meant by exposure? To quote Bryan Peterson from “Understanding Exposure”, he says the correct exposure is a
“combination of your choosing the right size hole in your lens (the aperature), and the right amount of time that light is allowed to remain on the digital sensor (shutter speed) and how both of these factors are influenced by your choice of ISO”.
Given that Bryan has written a whole book on exposure, I’m obviously just touching on the surface with my very small blog posts!
To really start learning about the relationship of the triangle, it’s best to move away from the fully automatic settings on your camera and give the Manual (M) function a go. This really helps you learn the impact of changing ISO, aperature and shutter speeds. I must admit though, for now, my default mode is Aperature Priority (Av in Canon), where I can select what aperature I require and adjust the ISO, but the camera automatically selects the appriopriate shutter speed to achieve the right exposure. If I wanted to be truly lazy, I could even put the ISO into auto mode too, but as I’m trying to learn, I don’t think that teaches me much!
Now, depending on what you’re trying to achieve, you now have the ability to adjust 3 key variables on your digital camera. Broadly speaking:
APERATURE controls the amount of light that reaches the camera’s sensor.
What to think about?
- Depth of field (ie blurry or clear backdrop)
- What level of ambient light is available?
- The lens length you’re using can also impact/restrict the aperature size you can achieve.
SHUTTER SPEED controls the length of time the shutter remains open.
What to think about:
- What are you trying to achieve creatively?
- Is the subject moving? Do you want to freeze the action or achieve blur to create a sense of movement?
- Having you considered panning? It’s fun to try! You get a subject matter that’s focused, with a blurred background. It takes a while to work out what shutter speed is best, but I’ve tried it with my son on the swings at the park. (Blocked out his face for privacy reasons!)
- Do you have a tripod to help you with really slow shutter speeds (generally due to low light) to minimise camera shake?
- What’s the ambient light like?
ISO/SENSITIVITY is a blog post in itself (which I’ll do on another rainy day)! Sometimes, depending on circumstances, no matter what setting you’ve selected for aperature or shutter speed, you’ll need to adjust the camera’s sensitivity to light, done by altering the ISO setting.
Here’s an example. The shutter speed may be too slow and the images are blurring through camera shake. By increasing the camera’s sensitivity by changing the ISO from say, 100 to 200, this will essentially increase the light by 1 stop (f stop). Just briefly below, the images show the Aperature set at F9.0 and the shutter speed at 1/100, but the ISO is drastically different, and that’s all down to the ambient light available. However, choosing varying ISO settings has resulted in getting a correctly exposed image.
I hope that makes sense for now. More on ISO to come. Later.