#8 Using the Exposure Triangle to get the correct Exposure

Part Eight – Using the shutter, Aperture and ISO settings to get the correct Exposure

In this video we look at how we can combine the Shutter speed, Aperture and ISO setting to get the right exposure for different creative effects.

Transcript of Video

“We’ve talked about each of the exposure controls in turn

Today we’re going to discuss how they interact with one another, the relationship that they have with one another and what settings we’ll use to get first, the correct exposure and second the create effect that we are looking for in the photography.

Let’s assume I’ve gone outside and taken a photograph of my favourite flower in the garden. It’s a bright summer day, it’s around midday so there is plenty of light available. The flower isn’t in direct sunshine but is very well lit.

First I put the camera on manual, I will be using the camera built in light meter to work out the correct exposure, but I want to dial in the exposure controls myself without the camera doing it for me.

I’m going to set my shutter speed at 1/60 of a second because I am going to be hand holding the camera and I know if I shoot with a shutter any slower than this I’m going to get camera shake, so I want to avoid this.

Next I set my ISO on 100 because I know there is enough light around to use a lower ISO setting and I want the best quality of photograph available. I don’t want any grain like noise visible in the final image. If I was photographing later in the day there would be less light available and I may need to use a higher ISO.

Now I need to balance the exposure using my aperture.

I look through the viewfinder and frame the image as I want it to look in the final photograph and use the cameras built in light meter to help me get the correct exposure. I use the exposure scale in the viewfinder to work out where I need to set the aperture so that the needle is in the middle of the scale. As I move the aperture control it goes to F11 as the needle moves into the centre of the scale.

Now I know this is the correct exposure setting.

I have the shutter on 1/60 the ISO on 100 and the aperture on f11 I know this will give me a perfectly good exposed photography. Not to light and not to dark.

Getting the correct exposure is my primary concern, once I’ve achieved that then creative influences come into play.

Let’s assume I want to get a shallow depth of field. I want a sharp flower with the surrounding flowers and leaves in front of it and behind it out of focus so that one flower is isolated and the viewer’s eye is drawn to it. Now that’s a creative judgement and I know I need to adjust the aperture to achieve that.

I know I need to open the aperture as wide as possible to get the effect I am looking for.

Now let’s assume that the maximum aperture available on my lens is f4.

So if I am going to adjust the setting from F11 which is giving me the correct exposure to f4 so that I can get a shallow depth of field, I am moving the aperture by 3 stops. f11, the next stop is f8, f5.6 and f4. Now that means we are letting 3 stops more light into the camera which will throw out our exposure by 3 stops

So we need to do something with the other 2 controls to offset the extra light that’s coming into the camera.

I’m not going to alter the ISO because the ISO is the last thing that should be changing so that I maintain the best image quality. And an ISO of 100 on my camera gives me the best image quality, so I’m not going to touch that

So I’m going to just use the shutter speed to get back to the correct exposure.

Now I’ve let 3 stops more light in through the aperture by moving it from f11 – f4 so I need to let 3 stops less light in through the shutter to balance that out and bring it back to the correct exposure.

So I’ve got the setting of the shutter on 1/60 of a second. so if I speed that up, and if I speed the shutter up I’m effectively letting less light in. so if I speed it up by 3 stops I’m going from 1/60, 1/125, 1/250, 1/500 of a second. That’s my 3 stops. if I set the shutter on 1/500 of a second with my aperture on f4 and an ISO of 100 that will give me exactly the same exposure as when the camera was set on 1/60, f11 and iso 100. It’s letting in exactly the same amount of light into the camera.

Now I chose the change the camera to the second setting for creative purposes and I wanted to get a certain effect namely a shallow depth of field.

But the two setting give me exactly the same exposure.
Now the example I’ve given you is a hypothetical situation. what I would suggest if it’s daytime where you are, is go outside with your camera set your shutter on 1/60 have your iso on the lowest setting possible my cameras lowest setting is 100, yours might be 50 or 200 whatever is the lowest setting available on yours.

And then balance your exposure with you aperture.
And whatever your camera meter indicates is the best exposure write that down.

And if your aperture isn’t already wide open, change it to the wide open setting. And have a look on the aperture illustration that shows you the sequence full stop aperture settings. And check how many full stops you have adjusted that from your original setting. And then counteract that by speeding your shutter by the same amount of stops.

That will give you exactly the same exposure but will give you a completely different effect in terms of depth of field.

I would suggest you pause the video right now and try it yourself so you are not just taking my word for it. And you can see it yourself.

Now let’s assume that we want to photograph the children playing in the garden, running around and enjoying themselves

And we want to freeze any movement so there is no blurring in our photography.

To achieve this we need a fast shutter speed.

Now the shutter speed we used when balancing our exposure for the shallow depth of field photo which was 1/500 second is probably fast enough freeze action. so we could just use this setting to take the pictures of the children.

But let’s assume we want to speed our shutter up a little bit to say 1/1000 of a second just to make absolute sure there’s no movement in the photograph.

So we move the shutter by a further stop from 1/500 to 1/1000 which is letting in a stop less light into the camera. Now again we would need to balance the exposure by letting in a stop more light using either the Aperture or ISO.

We would look to altering the Aperture first but have encountered a problem. We already have the Aperture wide open at f4.

So we are unable to let more light in through the Aperture on this particular lens and without having to go out and get a lens that opens up to f2. 8.

So in this circumstance we could use the ISO to allow more light into the camera. We want to use it as a last resort but in this instance we have no option. The aperture is max’d out so there is nothing else we can do other than increasing the ISO by a stop from 100 to 200 to balance the exposure”.