An introduction to ISO, aperture and shutter speed:
When I started this blog, I knew that sooner or later, I would have to face the technicalities of ‘The Big Three’ – ISO, aperture and shutter speed.
If you are vaguely interested in photography (which I imagine you are if you’ve found your way onto my blog) you will surely have heard of at least one, if not all, of these three key elements. If you’re anything like me though, you will have avoided this daunting subject and kept your camera firmly switched to auto, rather than dare to try and understand such mysterious concepts.
I bought my fancy camera with the intention of improving my photography and, in order to do that, I believe I need to delve deeper into the technical aspects that affect the way an image is captured. It has now been four months and I can’t avoid it any longer. So here is my basic (and hopefully pain-free) guide to The Big Three.
Overview
When people talk about the ‘exposure’ of a photograph, they are referring to how much light is let into the camera. If there is too much light your photo will be too bright and the colours washed out (overexposed). If there is too little light your photo will be too dark (underexposed). Either way, your photo may lose the detail and quality you were hoping for.
By adjusting the ISO, aperture and shutter speed of your camera you can find the correct exposure for your images. How you adjust your settings will differ depending on the camera. Most cameras will have a dial showing ‘M’ mode for manual adjustments. You may also have ‘S’ mode for shutter priority and ‘A’ mode for aperture priority. The priority modes will allow you to have manual control over one element while the other elements are handled automatically.
The auto mode on your camera will try to make exposure adjustments for you, but may not give you the results you want. For full control and creativity you will need to learn how to adjust your settings manually.
ISO
The ISO setting on your camera controls how sensitive the image sensor is to light. A low ISO means lower sensitivity, so more light is needed to produce a correctly exposed image. This means it is better to use a low ISO in bright situations.
A high ISO means higher sensitivity to light and so less light is required for the exposure. If you want to take photos in a dark environment you will need to set your camera to a higher ISO. A high ISO can result in a more grainy image so it is best to use the lowest ISO possible for your situation.
Below you can see two photos taken in bright light. The photo on the left has a low ISO while the one on the right has a high ISO. If you enlarge the images you will see that the photo with the high ISO is much more grainy.
Aperture
The aperture is the hole within the camera lens that allows light to pass through to the sensor. The size of the aperture can be adjusted to increase or decrease the amount of light that is let through.
Aperture is measured in ‘f-stop’ numbers (e.g. f5.6). Confusingly, a high f-stop number means the size of the aperture is small and less light can pass through. A low f-stop number means the size of the aperture is big and more light can pass through.
Aperture also controls how much of an image is in focus, or within the ‘depth of field’. Depth of field refers to the distance in front of and behind your subject that is sharp and in focus. The depth of field is affected by the aperture, the type of lens you are using and the distance you are from your subject. A large aperture (low f-stop number) creates a narrow area of focus, while a small aperture (high f-stop number) creates a wide area of focus.
The photo on the left below has a large aperture and therefore a narrow area of focus, meaning the plant is in focus but the background is blurred. The photo on the right has a small aperture (wide area of focus) meaning both the plant and the background are in focus.
Shutter speed
Probably the most straight forward of The Big Three, shutter speed refers to how long the camera shutter is open for. A slow shutter speed allows more light through to the sensor and so can be used in darker conditions or to produce motion blur effects. A fast shutter speed allows less light through and is good for catching quick movements.
The photos below were taken using increasing shutter speeds, from slow on the left to fast on the right.
Understanding the principles of The Big Three is pretty straightforward, but putting them into practice and learning to use them with ease will take a bit of time and perseverance. Once mastered, however, the results are very satisfying and worth the effort so don’t give up!
You will need to choose your ISO, aperture and shutter speed based on the environment you are in, the subject you are shooting and the kind of effect you want to create. Experiment by shooting the same image with various settings to see the difference your manual adjustments can make and to find out what works best.
CNL
Katie x
Camera Never Lies 
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