 So, what is wrong with this photograph? Well, if you know a little bit about photography, you might say this is under exposed, under exposed. And this is a term that has to do with, and it's related directly to today's topic, which is exposure. So, it seems like it might go together, exposed and exposure. But the question is, what does this mean? What does under exposed mean? Or what is exposure? Exposure is a way of measuring how well you have done getting the right amount of light onto your film. So, imagine over here we've got a piece of film or a digital sensor, just light sensitive, something I always seem to use the little brown squigglies for that. So, you've got your camera, you've generally your film or your sensor is hidden away from all the light. And when you open up your camera by taking a photograph, it pops open the shutter, light rushes in, and it's exposed, so it touches your film or your sensor. And then it creates a sort of either a chemical or a electric reaction where the light interacts with that surface, and it creates then an image as a result. And that image is measured as, is measured partially for its exposure. That exposure is just a measure of how much light it picks up while the shutter is open and while the sensor or the film is exposed to light. So, this is a really important thing because exposure has to do with the quality of an image, how it looks. You want to have good exposure so that your photographs are crisp and clean and look nice. Well, now what does it look like when you do the opposite? It looks like something like this. This is overexposed. Overexposed just means too much light fell on the sensor or on the film, and all the colors are washed out, all the darks are gone. You can see the light, the darkest thing you have on here is sort of still a pretty light color. So, that is overexposed. Now, this is somewhere closer to the correct exposure, so still not perfect, but a little bit closer. And you can see here that now I've got tones that range all the way from a high white, so a very bright white, down to a pretty dark true black, almost. So, you know, we're here especially the true blacks and lots of things in between. Now, tones are not actually colors. Tones are sort of like a range of, I guess, the amount of light that an object gives off. So, you can see here that this is a white tone, this is a gray tone, and this is sort of a black tone. And everything in between is a part of the tonal range of an image. And what your camera is trying to do when it's looking for exposure is it's trying to create sort of a contrast range that has a little bit of dark, a little bit of light, and lots of in between. So, when your camera looks at this scene, it wants to make 18% gray. It sees everything in black and white, and it's like, we want to make it 18% gray so that everything averages out. So, if you were to take all the color or take all the tones, so you take the black and white version of the image and throw in a paint mixer, the resultant color would be 18% gray if your meter had it its way. But sometimes that doesn't always match reality. And in reality, this scene had a lot of darker tones in it and a lot of lighter tones. But ironically, when it sort of works out, it comes out to about 35% gray. So, here you can see the problem that metering and exposure create for photographers. You've got your camera wanting to make 18% gray. Your photo isn't actually full of anything that's 18% gray. It's actually, if you look at it, it's about 35% gray. So, you want to try to find a way of tricking your camera into exposing correctly for the 35% that it actually is, not the 18% that it wants to make. Let's try and now to make really quickly sort of a diagram of what is actually happening here. Let's imagine we've got a stool here and it is a three-legged stool. So, you've got one, two, three legs on your stool and they're kind of funny legs. Sorry about that. Now, one of your legs is going to be your ISO. This is going to determine how fast the photograph can be taken because you've got a certain sensitivity on your film. You're also going to have your shutter speed. We're just going to write shutter. This is going to be how fast the photograph is taken. So, how long the camera is open to the light. And your last thing is going to be your aperture. And this is sort of like the size of the window that's allowing the light into your camera. Now, you can imagine this as a three-legged stool where if one of the legs is too short, the stool falls over. So, the correct exposure is sort of like sitting, is sort of the flat stool that you imagine that you can sit on or put an egg on and it won't roll off. Now, if any one of these things is incorrect or not matching, then you're going to have a problem. Your stool is not going to be flat or usable, really. And sometimes this will be called the exposure triangle. So, these three things are all related. They're variables of good exposure. And if you change one, well, then you have to change others. So, just like if you were to shorten one of these legs, you would then have to shorten all of the legs or you'd have to sort of adjust them so that they would all create, then, a flat stool. A lot of times what a lot of photographers when they're first starting out, they will then first lock in one. So, for example, I always, it was really easy back when I started, ISO was always set by your film. So, you had a piece of film and then your only two variables were your shutter speed and your aperture and then you just could mess around with those two and always try to make sure that they were bringing everything into equilibrium. So, what you're trying to do when you're aiming for good exposure is you're trying to fill the film with a certain amount of light that it needs in order to expose the photograph correctly. And you can kind of imagine, then, the film or your sensor to be sort of like a bucket. So, we're going to write film or sensor here. And your bucket, you can change the size of your bucket. So, your bucket can be big, it can be small. And in this case, you could think of a small bucket as being a film with high ISO. So, it doesn't take very much water to fill a very small bucket. It doesn't take very much light to fill a very sensitive piece of film or a sensor. So, something at ISO 800 is like a very small bucket. So, you're trying to imagine that you need, you know, maybe this much water in your bucket no matter which bucket you have, if it's a big bucket or a small bucket, you need to have it, you know, maybe reach this 70% full level or something like that, say. And you're doing this with a pipe. So, the pipe is running from here to here. You've got your pipe right here. And you're running water through it. And you can change, then, with this, in this setup. You can change how long the water runs. You can change how big the pipe is. And you can change the size of the bucket. So, I'm going to make sure it makes inside. Now, the length of time that the water is running into the bucket is sort of like your shutter speed. So, just like you can open the shutter of your camera for a really long time, you can open the faucet and let water run for a really long time so that it fills up the bucket. Even if you have a tiny pipe, your pipe could be really mini. It could be like a F-22 pipe, so a really tiny pipe. But, and it could take, therefore, a long time for the water to go through and fill up your bucket. But, at the same time, you could also maybe spring for a bigger pipe, so you could maybe make the pipe like this big, and then you've got tons of water coming through, which, therefore, means you don't need as much time to let the water run through, or in this case, you don't need as long of a shutter speed. So, you can let more water in more quickly. That's really important. So, remember that your aperture is like the size of the pipe. Not the length of the pipe, but the width of the pipe, how much bandwidth it has, how much water or light, in the case of a camera, is able to pour through and into your bucket. And your shutter speed is the amount of time that you have, that you're running that water through, and your sensor is the size of the bucket itself. And all of these things are adjustable, so you can run the water longer, you can make the pipe bigger or smaller, and you can change the size of the bucket. And either way, you've kind of come up with a piece of math that, again, is a triangle. So, you have these three variables, and you have your aperture, your shutter speed, and your ISO. Each image has an interesting and unique combination of these things. So, right here, we've got our ISOs. So, say ISO, shutter, let's put shutter with SH, and we'll have our F stop right here. Now, this image to the left was taken on a bright evening at ISO 200. Its shutter speed is about a 500th of a second. And it was taken at around F 5.6. So, it's pretty standard for an evening, bright day. That's about a pretty average shot, really. This shot was the Irish Cottage. It was a cloudy, rainy day. It was ISO 200 still, though. I took the shot, though, at a 100th of a second. And it is also at F 5.6. So, you can see here, one, you can see here, that we've got our, we've got the same bucket. So, it's the same 200 size bucket. But in this case, I let the water run on the Irish Cottage. It ran a lot longer, 500th of a second and 100th of a second. So, that's a lot faster, that's a lot faster, this image here of the abandoned airport than of the Irish Cottage. Because I didn't have as much light. So, I just didn't have as much light to expose the film. And so, I needed a little bit longer to do that. Now, I'll take a look over here at the Berlin situation. So, here I'm standing on top of a house looking out over downtown Berlin. You can see the TV tower is very far away. And that is actually taken at a 400 ISO. Shutter speed was 115th and the F-stop was 5 points, I'm sorry, 3.5, I need to concentrate here, 3.5. All right, so, what's going on here now? We've got a bigger bucket, first of all. So, the bucket is, sorry, a smaller bucket. I need to remember my own metaphors here. So, you've got a smaller bucket. So, it takes less time to fill that bucket. And we've got now more, the water's running for even longer. So, we've got a 15th of a second which is a lot more than a 100th of a second and even more than a 500th of a second, so a lot more. And in this case, the pipe is actually a lot bigger because we've got a smaller number. So, a smaller number means a bigger pipe. And in this situation, we've got a 3.5 F-stop which means that it's almost one entire stop of light difference between here. And this is a very, very important concept. You will all have to memorize from the shutter speed lesson and from the aperture lesson that you've got sort of these variables. So, for F-stops, for example, you have maybe F-4 and then you have F-5.6 and they're one stop away from each other. Really important to remember, so that's one stop. You also have, for example, maybe 125th of a second or a 100 and 250th of a second and you've got 125th of a second. Now, that is also one stop of light. So, shutter speeds can be one stop of light. So, shutter speeds can be one stop of light and F-stops can be one stop of light away from each other. And that is a really important thing to remember because another important thing is that your ISO speeds are also one stop apart. So, if this was 100, for example, right here instead of 200, you would then have to change this shutter speed and cut it or you'd have to cut it in half or you'd have to double it, I guess. So, it's kind of hard to explain with these numbers but you would have to move, if you were to move this down to 100, you would have to move this shutter speed up to 250th because you have, in this situation, you have doubled the amount of time that you need to expose that image and therefore you need to either double the amount of time or if you don't do that, so say you were not to double the amount of time that you need, you would have to add more light so you'd have to move this to F-4. So, you've moved one stop here. So, we've got minus one stop. So, now we need to add a stop somewhere else or so we've added our stop here and the same thing if you were to do that, you know, maybe to this 400 here, say you were to say, take this and make this 100 speed film. Well, that means that's two stops. So, we've got minus two stops here and that means you need to make up for it somewhere else. Well, you can't really make it up for it here because maybe your lens isn't faster so you'd have to just, you have to just do it with your shutter speed. So, that means you'd move down to an eighth of a second and then down to a quarter of a second. So, you would already be at a very slow photograph right there. So, here you've got your plus two right here. So, it's always a matter of remembering these distances and that's why it's important to go back and take a look at what the difference between F4 is and F5.6 and F8 and remember the traditional stops, the traditional full stops so that you know for each photograph that you're taking, how many stops you have to move each of these variables when you're shooting manual photographs. All right, so that was your lesson about exposure and check out more lessons like this at alversity.org.