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9. How Aperture, Shutter Speed, ISO and Light Work Together 

Till now we’ve been learning about each setting individually.

But now it’s time to go to the next level and learn how these three settings – Aperture, Shutter Speed and ISO work together.

The three of them together is referred to as the Exposure Triangle.

And understanding this exposure triangle is the key to understanding how photography really works.

And the tool that will assist us in learning this is called as the exposure meter.

Exposure Meter

Look at the images below from Canon and Nikon cameras respectively:

The highlighted part is the exposure meter.

It basically looks like a number line with different markings.

As the name suggests, the exposure meter determines what the exposure of the shot that you are trying to take is.

Basically, that means it tells you whether the shot that you are about to take will come out overexposed (too bright), underexposed (too dark) or of the perfect exposure (not too bright, not too dark).

What Does the Exposure Meter Signify?

When the meter is pointing to the right (positive side), like shown in the image below, it means that there is lot of light reaching the sensor and the shot that you are about to take will come out overexposed.

So you can get a shot that looks like the one below:

The more away from the centre it is, the more overexposed it will be.

Note that in some cameras, the positive and the negative sides are the other way round. Also, in Canon cameras, you have to half press the shutter button to activate the meter pointer.

When the meter is pointing to the left (negative side), like shown in the image below, it means that there is less amount of light reaching the sensor and the shot that you are about to take will come out underexposed.

So you can get a shot that looks like the one below:

The more away from the centre it is, the more underexposed it will be.

What you have to aim for is for the meter to be in the centre like in the image below:

When it’s near the centre, you will get a well exposed image which will neither be too bright nor too dark.

How to Change the Reading on the Exposure Meter?

Watch the video below to see what to do. Alternatively, you can read the description too.

Video 15: How the Exposure Meter Works

Nikon users, click here to watch the video

Canon users, click here to watch the video

The reading on the exposure meter changes when you change the value of any of the following: Aperture, Shutter Speed and ISO.

Depending upon whether that change resulted in letting more light into the camera or less light into the camera, the meter will move accordingly.

For instance, let’s say the f-stop was f11 and we decided to open up the aperture by lowering the f-stop number to f3.5.

This will mean more light is coming into the camera. Hence the meter will start to move towards the positive side.

Similarly, let’s say the shutter speed was 1/500 and we made it 1/1000. This meant that the shutter now closes at even faster than before. So this will cut out the light reaching the sensor and hence the meter will move towards the negative side.

Going by the same logic, any changes in ISO make the meter react in a similar way. Suppose the ISO is 1600 and you change it to 400. As a result, the sensor becomes less sensitive to light, which as we learned before, basically means the shot is going to be darker than before. Hence, the meter starts to move to the negative side.

Just play around with the settings and see how the meter reacts. You’ll start to understand that the meter is basically reacting to the light coming inside the camera. More specifically, it is reacting to the sensor’s reaction to light.

I want you to try one more thing.

Just point your camera somewhere where this is a lot of light, like at a bright window or a tube light.

You’ll see that the meter moves towards the positive side. This because when you are pointing your camera towards something bright, more amount of light comes into the camera.

Next, point your camera towards something that is in shadows or in a dark area, like the inside of a cupboard.

This time you’ll see that the meter starts to move towards the negative side.

So basically, just like we learned before, everything in photography revolves around four things:

Aperture, Shutter Speed, ISO and the environment you are shooting in.

The next part will make you understand that getting the meter in the centre and shooting is just half the battle won.

The more important part lies in choosing which settings to use to get it in the centre, and that is something that will change with every shot because every shot has a different objective attached to it.

The next part will also show you why it is so important to let as much light in the camera as possible so you can keep the ISO low and achieve clean looking shots.

In the next part, we’ll be going through some case studies in order to understand how different situations require settings to be changed in a different manner in order to achieve the desired result.


Case Studies

In this part, we’ll be going through some case studies that will fortify our understanding of the manual mode. We’ll be forming a step-by-step methodology to shoot the photograph that each case study is talking about. So let’s get started:

Goalkeeper Case Study

Let’s assume that the editor of a sports magazine has approached you to take a few shots of a football match that they want you to cover for them.

The goalkeeper of one of the teams playing in the match is a renowned professional. They’ve specifically asked you to take a lot of shots of him when he’s in action, most preferably when he has jumped in the air to stop a shot.

The editor tells you that as long as the goalkeeper is sharp in the shot, nothing else really matters.

So let’s say we are talking about a shot that looks like the one below:

Can you guess what will be the most important setting here?

If you guessed shutter speed, then you’re correct!

Because we have to freeze the goalkeeper in flight, shutter speed is the most important setting.

Let’s say we are getting ready to take this shot and our camera is set to the following settings:

Aperture: f22

Shutter Speed: 1/10

ISO: 400

You know that you cannot go ahead with these settings and take the shot because a shutter speed of 1/10 will end up blurring the goalkeeper as he’s moving very fast.

Let’s say that for this particular shot, we need a shutter speed of 1/1000 to freeze the keeper.

So the first thing you would do is to increase the shutter speed to 1/1000.

Now how will this impact the exposure meter?

Because you went from 1/10 to 1/1000, the meter will start to move towards the negative side, indicating that you are losing light.

So if you were to take the shot right now, you would be able to take the shot but it would come out underexposed, like shown in the image below:

So how can you solve this problem?

You will have to use some other setting to raise the exposure of the shot.

An amateur photographer may straight away jump to increasing the ISO.

Even though that can solve the problem, ISO should not be the first thing that should come to our mind because increasing the ISO also increases noise.

So a better way to let in more light into the camera would be through aperture.

Right now the aperture is set to f22. This means that the aperture hole is really narrow and therefore, restricting a lot of light from coming into the camera.

So if we go from f22 to f3.5, we can save a lot of light.

But before doing that, you have to think of the impact this will have on the look of your shot.

You know that at a smaller f-stop number the background will get blurred.

So you have to ask yourself the question – Is blurring the background here a good thing or a bad thing?

The answer to that will lie in the objective of the shot.

Remember that the editor told us that the most important thing in the shot is that the goalkeeper comes sharp.

So we have the liberty to blur the background. In fact blurring the background will make the goalkeeper appear even sharper as he will be more isolated.

So going from f22 to f3.5 will help us in two ways – blur the background and save light.

As you go from f22 to f3.5, you’ll start to see that the meter starts to move towards the positive side.

Let’s say at f3.5, the meter comes in the centre.

Now you are ready to take this shot. The shot will look something like this:

You can see that the background has got a bit blurred but that’s fine because the goalkeeper is still sharp and that was our main objective.

More importantly, it’s a clean looking shot because we never had to raise our ISO as we used aperture to save light.

Now, let’s add a little twist to this plot.

Let’s say that the editor tells you that the viewers need to see the surroundings, so getting the background sharp is equally important.

Now this spells trouble. Why? You’ll soon come to know.

Your shutter speed is set to 1/1000.

The aperture is f3.5.

The ISO is 100 and the meter is in the centre.

But you cannot go ahead and take shot because of the new requirement that has been put forth by the editor.

You know you have to get the background sharp too this time.

So the first thing you will do is to increase your f-stop number. Let’s say we go from f3.5 to f16.

F16 should do the job, but what impact does it have on the meter?

Since we just made the aperture hole narrower, the meter will start to move towards the negative side.

Now, if we take a shot, it’ll have the goalkeeper and the background sharp, but will again be underexposed.

So we have to get somehow increase the exposure. So what can we do?

Can we let in light by reducing the shutter speed? The answer is no. Even though reducing the shutter speed may let in more light, we cannot risk blurring the moving goalkeeper. There is no point in having a clean looking shot if the subject itself is blurry.

Can we open up the aperture by using a low f-stop number? The answer again is no. Doing that will blur the background like in the last shot. But this time we want the background in focus so we cannot save light by aperture.

So there is only one option to bring the meter in the centre. And that is by increasing the ISO.

So you increase the ISO value till the meter gets in the centre.

Then you take the shot. It will most likely end up looking like the image below:

It’s not a desirable image as it contains a lot of noise but there’s not a lot that you could have done about it.

Just one more thing before we end this case study.

Let’s say you are the kind that just won’t give up. So you take it as a challenge to improve the last shot we took.

Let’s assume that you can ask the editor for ANY favour? What would it be?

You still have to get the goalkeeper as well as the background in focus so you definitely cannot do anything as far as the camera settings are concerned.

But can you do something about the ambient light?

Yes, you can.

Remember I said ANY favour.

So one thing you can ask is if it’s possible to direct a floodlight right in the direction of the goalkeeper.

This would increase the amount of ambient light present in the area.

This would in turn push the meter towards the positive side, thereby allowing you to reduce the ISO to get it back in the centre.

Hence, you will be able to achieve a cleaner looking shot.

Landscape Case Study

Let’s say you are trying to take the shot below:

Can you guess what’ll be most important setting this time around?

If you guessed Aperture, you are correct!

In a landscape shot, it’s important to get all the focal planes in focus right from front to back. Hence, we need a deep depth of field.

A large f-stop number enables us to do that.

So let’s say our settings are the following:

Aperture: f3.5

Shutter Speed: 1/500

ISO: 400

The first thing you would do is to increase the f-stop number. Let’s say you push it up to f16.

This would move the meter towards the negative side. If you were to take the shot now, it would come out underexposed like this:

So how can you get the meter in the middle?

Again, amateur photographers will simply resort to increasing the ISO.

But a smarter photographer knows that ISO should be the last resort as it results in noise.

So a smarter thing would be to ask yourself – Is anything moving in the scene?

The answer is no.

If nothing is moving, then can you use a slower shutter speed?

Yes, you can.

So the right thing to do here would be to lower the shutter speed.

But before we do that, first reduce the ISO all the way to 100. This is because we’ll be able to save all the light by using a very low shutter speed, so there’s no need for even an ISO of 400.

Once ISO is set to 100, you’ll see that the meter has further moved towards the negative side.

But now it’s not a problem?

Because all we have to do is to keep reducing the shutter speed till the meter comes in the centre.

So let’s say we keep reducing from 1/500 and find that the meter came in the middle at 1/5.

Now we’re ready to take the shot. We’ll get a clean looking shot.

Let’s complicate things a little.

Let’s look at the shot below:

This is still a landscape shot, but this time there is one difference. And that is that the blades of grass are much longer.

Let’s assume that the wind is strong and that these blades of grass are moving.

This time, can you reduce the shutter speed all the way down?

The answer is no.

Why? Because there is movement.

So you can only bring down the shutter speed up to a certain point. Let’s assume that after some trial and error, we find that a shutter speed of 1/80 is sufficient to freeze the moving blades of grass.

So you can save light up till 1/80 but you cannot go beyond that or you risk the blades of grass turning blurry.

Now the meter will not have moved entirely in the centre as you had to stop at 1/80.

Now the only option left to get the meter in the centre is to increase the ISO.

This will increase the noise in the shot but there’s not much you can do about it.

Now let’s come back to the first shot that we talked about. Have a look at it again:

For this shot, we learned that we could easily use ISO 100 as there was no movement. We got all the light in the camera by using a very slow shutter speed.

But what if I tell you at this moment that you have forgotten about one very important movement?

Think about it.

Can it be the clouds? The answer is No. In fact just like water, clouds actually look very nice and artistic when their movement is blurred. So a slower shutter speed would be great for clouds to produce a nice blurry effect.

Can it be the grass? The answer is No. We’re assuming that the grass here is so short that it’s not really moving by the wind.

Then what is it?

I’ll give you a hint.

The hint is that this movement that I’m talking about cannot be seen by you when you look at the shot.

Have you guessed it?

Here is the answer.

The movement that we completely forgot about here is OUR OWN MOVEMENT WHILE TAKING THE SHOT!!

You see when we shoot the camera handheld, it is impossible to stay absolutely still. There is bound to be some movement of the camera due to the movement of our hands.

This is referred to as a camera shake.

A camera shake is not a big problem when you are using faster shutter speeds because the shot is taken so fast that the minor camera shake due to the movement of the hands becomes irrelevant.

The problem comes when we are using slower shutter speeds.

This is where a camera shake can cause a shot to look blurry not because the subject was moving, but because the camera itself moved.

When shooting handheld, any time you go below a shutter speed of 1/40, you’re always taking a risk.

1/40 is not a universal rule. It’s just an average. Some people don’t even go below 1/50 or 1/60 when shooting handheld. While others who have a more stable technique and like to take risks can shoot handheld even at 1/10.

But for the purpose of this book, we’ll stick to 1/40. So if you’re shooting handheld, you should not be going below a shutter speed of 1/40.

So coming back to our original shot, let’s have a look at what we should be doing with our newly gained knowledge.

Previously, we just kept on decreasing the shutter speed till the meter came in the centre and took the shot.

But now we know that even though there is no movement in the scene, we cannot decrease the shutter speed all the way down as we are shooting handheld.

So we can only go down till 1/40.

Once we reach 1/40, we’ll find that the meter is till pointing towards the negative side.

So we’ll have to increase the ISO till the meter comes in the centre. Then we can take the shot.

But it will contain some noise.

But as you’ll learn in the chapter on landscape photography, it’s almost a must to shoot landscape shots at ISO 100 as that’s where they look the cleanest.

So how do we achieve this?

The answer lies in using one of the most popular accessories in photography – THE TRIPOD. In the next chapter, we’ll learn how to use the tripod with the help of an exercise. This exercise will also make it clear how ISO works and how you can reduce noise in shots by shooting at a lower ISO.

Next Chapter: The Tripod and Its Usage