Aperture, ISO and Shutter Speed – When to change what

Aperture, ISO and Shutter Speed – When to change what

This week I’ll be showing you when and why you’d want to change your Aperture, shutter speed or ISO.

The three most important settings to get familiar with on your camera are Aperture, Shutter speed and ISO.

Either will change the exposure making it brighter or darker, however, they also change the image in other ways.

So when do you change what?

Basically, as well as changing the exposure:

Aperture will change the depth of field

Shutter-speed will change how much or little motion blur you have in the image

ISO will change how sensitive the sensor is, when the number is too high, it will also introduce “noise” into your image.


If you want as much as possible in focus, get your f number higher, up to about f16. This will make the depth of focus deep and bring a lot into focus. If you want a small part to be in focus, drop the f number as low as possible. This will make the depth of focus small and can give you the power, as a photographer, where you want the viewer to look. People are drawn to what is in focus, so this is very useful.


This controls motion blur. The lower the shutter speed, the more likely that moving things in your shot will be blurred. If you want motion blur to give the sense of movement, you can lower this to give this feeling, if you want no movement in your shot, you get your shutter speed as fast as possible. Just be careful of how low you go when shooting handheld. Like I mentioned in last weeks video, if you’re shooting handheld, keep your shutter speed the same or faster than the corresponding number on your focal length, so if you’re shooting at 50mm, keep it to 1/50 second or faster. If you’re using a 200mm, keep your shutter speed at 1/200 of a second or faster.


ISO is basically how sensitive the sensor is to light. We’re all told, and have learned to keep the ISO as low as possible (around 100) for a clean image, but sometimes this is not possible due to low light, so ISO gives you the ability and flexibility to be able to get the shutter speed and aperture where you want them. However, if you ISO is too high, the image will get noisy. This is basically where the image starts to look a little blocky or colours start to shift. Basically, the camera will start to struggle to see, a bit like our eyes do when it gets really dark.

So if you look at these different examples.

This is shallow verses deep


This is slow shutter speed vs high


And this is low ISO vs high.



So you can see, each setting has it’s own use, and remember, if you have a good exposure, and you change one value, you’ll have to compensate with one or both of the others to keep the good exposure.

Each of these settings also interact with each other. If you have a good exposure and you want to change one of the settings, you then have to compensate with one of the others. For example, if you want to open up your aperture letting more light in to get a shallower depth of focus, you would have to speed up your shutter or lessen the sensitivity of the sensor (drop ISO).

Or if you wanted to slow down your shutter, you would have to lessen the sensitivity of your sensor or make your aperture smaller.


And that’s about it. Just remember, first get good exposure and then change your settings to suit. Aperture controls the depth of focus, shutter speed controls motion blur and ISO controls how noisy/clean your image is.




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