Photography 101: Combining ISO, shutter speed and aperture

Think of a triangle where the three points are ISO, shutter speed and aperture. Somewhere inside that triangle is the perfect balance of these three things for the photo you’re trying to take.

This is the fourth in my ‘Photography 101’ series, aimed at helping people feel more confident with their camera. Ideally you’ll have read all of the others before now, although quick recaps are included here. For best results, follow the ‘Homework assignments’ and try the exercises. You’ll get to know your camera a lot quicker if you do. And if you like it hard then get ready – by the end of today’s session, we’ll be taking photos in full manual mode.

Think of a triangle where the three points are ISO, shutter speed and aperture. When your camera takes a photo, it balances out these three things to make a sharp (not blurry), well-exposed (not too light or dark) photo with no movement. Somewhere inside that triangle is the perfect balance of these three things for the photo you’re trying to take.

If you’ve been doing your homework assignments (and if not, see me after class for a spanking) then you’ll have started to notice the key things already, like how shutter speed really affects the brightness of a picture. So now, let’s start combining these three things.

There are a couple more homework assignments than in the previous posts but on the plus side, a little less waffling from me beforehand. If you’re up to date with your assignments, these won’t actually take you that long because you’ll be finding your way around the camera with more confidence.

Camera modes

If all you want from a photo is something sharp and well-exposed, leave your camera on automatic. Huge companies have invested billions of dollars trying to make cameras that can perfect that process for you – and you’ve paid hundreds of pounds for that product – which, lest we forget, is a computer more advanced than the one that took men to the moon – so why try to work it out for yourself? I can’t even work out what 47*3 is without #HeyGoogle.

Eventually we want to get to a place where you never take the camera out of manual mode, just like you’d never buy a computer-driven driverless car. Where’s the fun in that? But if you’re not ready to switch to manual just yet, there are two semi-manual modes that will help you take that first step.

Aperture priority

In AP mode, you get to choose what the aperture is and it balances out the other two settings (shutter speed and ISO) for you. Depending on your camera, it’s usually called AP but could be something else and if you’re using a phone app, you may not even have this option. Sorry about that. Buy a proper camera.

What’s the point of aperture priority mode if the other settings are balanced out for you? Well, remember that aperture does two things. It limits the amount of light coming through the diaphragm;  and it controls the depth of field (the amount of the photo that is in focus). Aperture priority allows you to set exactly the right depth of field without you worrying about the shutter speed and ISO.

Let’s look at how that works – but first, take a look at the photo below and read the notes.

Here’s a photo taken at F1.8, 1/125, ISO 800. Look closely at her eye. See how the pupil and lashes are very sharp? And how neat her mascara is? When I do mascara it’s like I was on one of the rides at Alton Towers at the time, but that’s not the point here. Compare how sharp they are to her eyebrow. Both extreme ends of the eyebrow are already starting to go out of focus. The same is true of her lipstick. When you’re working at F1.8, that’s the amount of depth of field you have to play with, so you have to get it spot on! When using F1.8 for a portrait, it’s normal to focus on one eye, the one nearest the camera if your subject is at an angle. Photo by PxHere used under creative commons.

Homework assignment – aperture priority

  • We’re going to take some close-up portraits. Find a willing model or simply bribe a nearby child with cash or the WiFi password (make sure it’s one you know). Put your camera in aperture priority, and set your camera to the widest aperture – check back to the Aperture article if you need a refresher on how F numbers work. Zoom out as far as you can, and then find a comfortable distance from your subject where their face fills most of the frame when they are facing you straight on. We don’t need much background.
  • Now, focus on one eye, and take your photo. Notice what the shutter speed and ISO settings are selected automatically by your camera. Stop down to the next aperture, and do the same. Check the settings. My guess is that only the shutter speed changes to begin with – am I right? Keep going until you have taken one picture at each F stop. Now go back and compare. If the eye is in focus, what about the tip of the nose, or the ear? At what F stop do they come into focus? What about hair; when does that become sharp and in focus?

Shutter priority

Sometimes marked as TV on cameras, shutter priority works just like aperture priority but with the emphasis on shutter speed. While you make changes to the shutter speed, the camera keeps the other two settings balanced so that it takes the sharpest, clearest picture.

You remember that the shutter also has two functions. Firstly, it limits the exposure of the photo by limiting how much time the shutter is exposed to light. But secondly, it allows us to capture movement in photos like in the extreme example below.

This is one of the Peak District reservoirs. I left the shutter open for so long that the surface of the water no longer even looks like water – the movement has just kind of blurred and evened itself out. The settings were ISO 100, F22 and an exposure of 30 seconds. In daylight, exposures this long are only possible with a neutral density filter, which we’ll talk about in, I don’t know, Photography 701 or something.

Enough waffle – shall we?

Homework assignment – shutter priority

  • Let’s capture movement. Put your camera into shutter priority, set it to the fastest shutter speed, and set it up near a sink – say, on the worktop in your kitchen. Turn on the tap and take a photo of the water coming from it. Then (you know the drill) keep reducing the shutter speed. At what speed does your camera stop freezing the water’s movement? At what speed does the water start to look smooth and milky? When does the picture get too overexposed? This is similar to the test I did with the hose, except I was too stupid to think about resting the camera on a solid surface when I did it.

Manual mode

Manual mode is just what it says – the mode where you have to make almost* all the decisions for the camera:

  • What to focus on
  • How fast the shutter speed is
  • How big the aperture is
  • What ISO to use

Understanding manual mode feels like a lot, but it isn’t. We’ve already broken down the main concepts and most of the time, when you’re using manual, you’ll focus on only changing one parameter. Usually you know what quality you want (the ISO number – you’ll go for the best quality you can, obviously) and the aperture choice is driven by how much of the background you want in or out of focus. So then, you just adjust the shutter speed until you get the light that you want. And if the shutter speed gets so long that you accidentally capture movement, you increase the ISO until you can adjust the shutter speed again. Don’t worry if that made no sense – we’re going to walk through it in a future episode.

* In another post we’ll have to talk about some of the more advanced features, like metering modes. But not just yet.

Homework assignment – manual mode

Okay, it’s time to take the leap. Put your camera in manual and let’s go take somes photos. Don’t worry, I’m not going to throw you in at the deep end quite yet.

  • To begin with, set your camera  to aperture F5.6, shutter speed 1/250, and ISO 400. In general, these settings are a good place to start, especially outdoors. Start off by taking pictures of different scenes and locations and see how those settings work with the scene. Literally, just wander round the house and garden and take snaps.
  • Choose one of the locations that is most underexposed – too dark. Start off by adjusting the shutter speed and then start taking pictures. What speed do you eventually have to change it to before the photo is correctly exposed?
  • Now, set the shutter speed back to 1/250. Do the same exercise, but change the aperture instead. At what aperture – if anyone – does the photo become correctly exposed? What does changing the aperture do to the picture apart from making it lighter?
  • Let’s complete the exercise. Make sure your camera is back at F5.6 and 1/250 of a second. Now, adjust the ISO until your photo is correctly exposed. Depending on your camera, you might not even be able to. But if you can, zoom as far into the picture as you can when it is correctly exposed. How does it look up close?
  • How do you feel about the end results? Do you think you can fix the underexposure by just changing one thing? Consider this – is it better to make a drastic adjustment to one setting, or is it better to make tiny adjustments to all three settings? Experiment with that idea. Put your camera back to aperture F5.6, shutter speed 1/250, and ISO 400. Then try changing everything in the smallest amounts. For example, instead of just changing the shutter speed to 1/30 and leaving the other two as they are, try going to F5, 1/200 and ISO 500 (or whatever is closest on your camera). Keep adjusting all the settings by one amount until you’re happy.
  • Finally, do the same again with the most overexposed picture you can find. Instead of me guiding you, figure out for yourself what you’re going to change. Start off by leaving the camera at ISO 400 and just change the other two settings. Only change the ISO if you can’t fix the exposure using the other two settings (which is the best way to do it. Only ever decrease the quality of your picture as a last resort).

A last word

At this point now you have hopefully discovered how aperture, ISO and shutter speed play together to create a technically sound photo, one that is sharp, in focus, and well-exposed. If you have done all the homework assignments I would be prepared to bet (although probably not prepared to pay up) that at some point you had a picture that you liked that wasn’t correctly exposed. Maybe it was too dark to be correct, but you liked the way there were only little parts of it that caught the light? We call that ‘low key’ photography. Most of my self-portraits are examples of low key photography and I’m very fond of the technique – I just feel like I look better in 100% shadow.

Maybe you had an image that went the other way. Maybe it was far too bright and it became almost abstract? That’s ‘high key photography’.

These are examples of when you break the rules with positive intention and a specific aim in mind.

If you just want to know how to use manual mode, congratulations – now you know! All you need to do now is practise. But if you want to learn about breaking these rules for creative reasons, carry on with the next two posts. After that, there’ll be a post on editing using levels and curves, and then we might get onto the really nerdy stuff (puts sexy scientist outfit on) like metering modes.

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