What Is Exposure In Photography? (A Beginner's Guide)
Hi and welcome to Episode 153 of the Photography Explained podcast. I’m your host Rick, and in each episode, I will try to explain one photographic thing to you in plain English, in less than 27 minutes (ish), without the irrelevant details. What I tell you is based on my lifetime of photographic experience. And not Google. Not in this episode. No, I know this stuff.
First - here is the answery bit
Exposure in photography is the amount of light that reaches the camera sensor when taking a photo. A correctly exposed image has captured the range of light in a scene correctly. An underexposed photo is too dark, with information not recorded in the shadows. An overexposed image is too light, with information not recorded in the highlights.
The exposure can be changed by changing the aperture, shutter and ISO. The relationship between the aperture, shutter and ISO is called the exposure triangle.
Photographers must understand exposure to ensure we know how to take photos correctly. You should get the right exposure every time you take a photo.
That was the answery bit. Here is the talky bit.
This is important. This applies to every photo that you and I take. This is a photography fundamental. And these principles apply to any device used to take photos, digital cameras, film cameras, and phones. The only variable is how you take the photos and what settings and adjustments are available to you.
Photography is drawing with light, and to do that correctly you need the right amount of light. Makes sense right?
And a word on this episode.
The intention was to explain exposure in one episode, but there is too much to it. So this is what I am going to do. I am going to tell you all the things that you need to know about exposure, and then next episode I will cover how you get the correct exposure - so this is the what and why episode, next episode is the how episode.
Why is this important?
This is very important. I will keep saying this because this is very important. Any level of competent photographer is expected to be able to get the exposure correct on any photo. For a professional photographer, it is just expected. Underexposed and overexposed photos are of no use to anyone. You have to get a proper exposure with every photo that you take.
Underexposed and overexposed photos are just not acceptable.
The only exception to this is if over or underexposing is done deliberately for creative effect.
You can't get back what you don't have.
If you underexpose or overexpose a photo you have missed some of the lights or darks. You have not captured everything. You cannot get this back. Sure there are things that you can do but the bottom line is that if you have not got the exposure correct you have not captured all of what you are photographing. Well, you have not captured the range of lights and darks that you should be capturing. More on this later.
And that can never be a good thing, right?
So this is important. I might have said this before.....It is important because if you do not get the exposure right you have not taken the photo correctly, and you might not get the photo that you intended. And worse still there is nothing that you can do about this after the event. OK, you can do all sorts of stuff with computers, but that is not the way it is meant to be.
Fixing things in Photoshop is no substitute for getting it right in camera.
What happens when I take a photo?
When the shutter release button is pressed, the camera shutter opens exposing the camera sensor to light. The amount of light that gets through to the camera sensor is controlled by the size of the opening in the camera lens, the aperture, and also how long the shutter is open.
The camera sensors' sensitivity to light can be changed by changing the ISO setting.
The correct exposure
A correct exposure records the correct range of lights and darks. Simple.
Underexposed photos
With an underexposed photo, not enough light has got to the camera sensor, meaning that you have not recorded all the light at the dark end of things, the dark bits, the shadows. You cannot get this data back.
Overexposed photos
With an overexposed photo too much light has got into the camera sensor, meaning that you have not recorded all the light at the light end of things, the light bits, the highlights. You cannot get this data back.
What does this mean
With a correct exposure, you have captured as much of the lights and darks as you can. With an underexposed or overexposed photo, you have not captured all of the light. You have missed some stuff that you should have captured.
Why can't I capture everything that I see?
Well, there is a technical problem with cameras. A camera cannot capture the same range of lights and darks in a single image capture as we can see with our own eyes.
- The range of lights and darks is called the Dynamic Range. In simple terms, this is a range of light, from light to dark.
- The human eye can take in 18-20 stops of light
- A modern camera can capture circa 12-14 stops of light
- My Canon 6D can capture around 10 stops of light - that is half what I can see!
I will talk about stops briefly in a bit.
What about exposure value?
Exposure value is a term that goes back to the film days. You can calculate the exposure value using a formula. Have I ever done this? No, I have not. So this is not something that we need to worry about ok? Let's move on.
Right - let's quickly look at how you control the amount of light in an exposure, and what the components of exposure are.
Aperture
The aperture is typically a metal-bladed thing built into the camera lens. You can adjust the aperture size to allow more or less light in. There are other things that changing the aperture does, but I will come onto them in a separate episode.
- Every camera lens has a maximum and a minimum aperture.
- The maximum aperture is the smallest number ie F2.8. The maximum aperture lets the most light in. Small aperture number = large or wide aperture.
- The minimum aperture is the largest number ie F22. The minimum aperture lets the least light in.
I know, it doesn't help us, some of this stuff!
As I say, there is much more to aperture such as depth of field, and all that good stuff, but this is the bit related to exposure.
On a phone, you probably can't change the aperture.
Shutter speed
The camera shutter is in the camera body. When the shutter release button is pressed the shutter moves, exposing the camera sensor to light. The shutter speed selected determines the length of time the camera sensor is exposed to light.
- A fast shutter speed lets less light in than a slower shutter speed
- A fast shutter speed is say 1/1000th second. This is a short exposure.
- A faster shutter speed can be used to freeze moving things.
- A slow shutter speed is say 1 second. This is also called long exposure.
- A slower shutter speed can be used to create motion blur.
Again, there is more to shutter speed than just the exposure time but this is the bit that matters when I am talking about exposure.
ISO
ISO in photography refers to the sensitivity of the camera sensor to light. This is a hangover to film days, more on this in a bit.
- ISO 100 is a low ISO. Use this in brighter conditions.
- ISO 3200 is a higher ISO. Use this in less bright conditions.
- The higher the ISO used, the higher the risk of digital noise and other bad stuff.
- ISO is also known as ISO speed, which is another hangover from the film days.
More on this in the episode all about ISO, can't wait for that one!
The exposure triangle
The exposure triangle is the relationship between the aperture, shutter and ISO.
The aperture and shutter determine how much light gets through to the camera sensor. ISO, the sensitivity of the camera sensor to light, determines how the sensor records the light.
The exposure triangle is going to be a separate episode all of its own. I want to do it justice. And this is very important. I don't want to give you half an answer here.
Is the exposure triangle complicated?
It is until it is not. It is one of those things that sounds complicated but when you get your head around it it is just fine. It took me a while, but I got there, and I will get you there as well with a future episode all about it.
Camera metering
Your camera has an incredibly sensitive, incredibly accurate light meter built into it. The camera meter measures the light that will be recorded on the camera sensor when you press the shutter release button halfway. This will determine how a correct exposure can be captured.
You can buy external light meters which are more accurate - I never have though.
Camera modes
OK then - we have aperture, shutter speed and ISO. How do we use these?
Well, if we use manual mode, we set them ourselves.
If we use a semi-automatic mode, we set two of them and the camera does the other for us according to the lighting conditions.
If we use an automatic mode, the camera chooses all of them for us. There are many different automatic modes, which have camera settings tailored to the subject matter being photographed.
Other exposure-related things.
Exposure is a big subject. Clearly. There are more things that I am going to cover in upcoming episodes - that is me sorted until mid-August! Seriously it is.
Right - some other things I will be talking about.
Histograms
A histogram is a visual representation of the light recorded in a photo. Histograms can be useful, I know people who use them all the time, but I also know people who have never used them.
So it is up to you, what I want to do is make you aware of them so you know about them.
Exposure compensation
This is a way of changing the camera settings very quickly to get the best exposure that you can. I use this all the time.
Bracketing
Bracketing is when you take more than one photo at a time, using different camera settings, which you will combine later. Remember that we can't get the range of lights and darks in a single photo that we can see with our own eyes? Well, this can help, giving us more at both ends of the scale.
HDR
HDR is High Dynamic Range. I have mentioned dynamic range before in this episode. HDR is not a bad thing, it is just another thing. And it is pretty much the same as bracketing.
Stops
Stops in photography. Another strange term in photography that I will explain. But in a nutshell (I love that term), a stop is a halving or a doubling of light. F Stop, exposure stop, f-stop values, or just stops, I will get to the bottom of this little lot one for all our sakes! And there is some work for me to do on this one.
Right – talky bit over - what if I use a phone and not a camera?
With a phone, you do not have all the adjustments that you have with a camera. Which is a good and a bad thing depending on your view.
And, with a phone, you have all sorts of computations and electronic trickery available to you, which is a good and a bad thing, depending on your point of view.
A phone will do a great job most of the time, but there are times when you need to do more, you need to change where the phone focuses or meters, or use an app to help you
I have just had a great idea. And another episode is born - how do I get the correct exposure with my camera phone? Perfect. That is one that I will need to do some work on though as I haven't looked into this.
What if I use a film camera?
Well, this is a new bit. What if I use a film camera? I have added this in as there are folks out there who are happily taking photos with film cameras. And I am sure there are professional photographers out there still shooting with film cameras.
Everything applies, apart from one thing. You have to get things right the first time as you don't have the opportunity to take loads of photos and check them to see if you have got things right.
And there is that one massive difference. To change the ISO you have to use a different camera film. Can you do this mid-roll? I think you can, although I am not 100% sure as I have not taken photos with a film camera for at least 20 years!
And I am going to include this reference to film cameras in future episodes. Well, why not? Film photography is still as valid as digital photography.
What do I do?
I use all of the above. But in my own way.
- I put my DSLR camera on a tripod, so I have automatically removed any issues with the shutter speed settings, and do not need to worry about camera shake.
- I set the lowest ISO that I can, which is normally 100.
- I use AV Mode, also known as aperture priority mode.
- The aperture setting I use is F8
- I use auto bracketing
- I compose the photo, normally using a 17mm focal length.
- I focus, meter and then press the shutter button. The camera takes three photos using auto bracketing. The camera chooses the shutter speeds for the three exposures.
- I merge each set of three photos together in Lightroom to give me one photo to edit.
That is what I do.
Some thoughts from the last episode
The last episode was How My One Photo Rule Will Help You Take Better Photos
Well these two are related, aren’t they? All I want to say here is that we photographers should all put our efforts into taking the best photos that we can. And with thought, time and care we can all do this.
Take time and care before you press the shutter release button.
Next episode
Episode 154 - how do I get the correct exposure? It was going to be all about aperture, but I need to spend some proper time on this. And then I will cover aperture, shutter speed, and ISO. And all that other good stuff.
Yes, this needs some time spent on it. There is no point rushing this just to do it quickly, that will not help you.
And now some stuff for you to do. And a favour
I have changed this. I didn't like what I was saying.
So this is the new bit.
If you have a question you would like me to answer just head over to PhotographyExplainedPodcast.com/start where you can find out what to do. Or just say hi. It would be lovely to hear from you.
That’s all.
This episode was brought to you by, erm, a cheese and pickle sandwich and a bag of salt and vinegar crisps all washed down with a nice cold Diet Pepsi, all consumed before I settled down in my homemade, acoustically cushioned recording emporium. Today's acoustic treatment is two pillows, two fleeces and a cushion.
I’ve been Rick McEvoy, thanks again very much for listening to my small but perfectly formed podcast (it says here), and for giving me 27 ish minutes of your valuable time. I think that this episode will be 25 minutes long after I have edited out the rubbish.
Take care, stay safe
Cheers from me Rick
