Controlling Exposure – TTL vs. Manual
now it's time to talk about exposure and controlling the exposure from our camera and from our flash. So Theresa is here to help me out with this demonstration in this section, we're going to talk about the fundamentals of controlling exposure for the ambient light and the light from the flash to remember that when you add a flash to your camera, one exposure becomes two exposures. We have the exposure of our ambient light, that's all the light that's zipping around. Like right now we have video lights here, it might be the light from the sun or lamps in a room, something like that, that's all the light that is just there that you can't control. And then you also have the light from the flash. So Theresa's got the speed light in her hand. And so we're gonna be controlling this light. And so what we want to do since we're using speed lights in a studio is we want to eliminate all of the ambient light and only work with the exposure of the light that's coming from our flash or flashes. S...
o that's really where we want to get we want to ignore all the ambient light, just get rid of that all together and then just worry about the exposure of these guys right here. So what we first need to do is figure out how to get rid of the ambient light. And once we do that, we're going to start looking at how to control the exposure from our flash flash exposure compensation and how the metering works and all that kind of stuff. So let's break this down step by step so I'm going to give this back to you, we're gonna begin by controlling our ambient light. So Teresa hop over here, we've got this sort of white and black wall we've set up on purpose to demonstrate this stuff and so what I have right now is my camera, my Canon R. Five and it is tethered to lightroom here and so what I can do is um okay yeah there we go. It was tethered and it was giving us a little hiccup. So what I'm gonna do is just take a shot of Teresa in aperture priority mode. So I'm an aperture priority mode and my aperture is at the F four. I'm at ISO 100. Nothing fancy. So click. Okay so I took just a normal photo here of Theresa. Let me bring this up on screen and you can see that this is 1/30 of a second at F four S. A 100. And it's just the light that we have in the studio illuminating our video, so not super flattering it's just a photo. So what we wanna do is we want to get this photo To a place where it's just completely black and then we're going to get rid of all of this light from showing up in our exposure to do that. What I'm gonna do is I'm gonna go to my camera. I'm gonna change the mode from aperture priority mode or shutter priority mode or any other mode. We want it to be in manual mode. Step one, put your camera in manual. So I've done that now we need to make our camera less sensitive to light because our little speed lights are really bright so they can overpower all of this ambient light. So what we're going to do is we're gonna set our S. O. To as low as it will go on this camera. 100 S. So 100 your camera might only go down to 200 It might go to 50 but you want to go as low as you can so that our light isn't sensitive to our main camera, isn't sensitive to this ambient light. The next thing we wanna do is our shutter speed. We're gonna talk about shutter speeds and sink and what sync speed is and all that kind of stuff uh in a session coming up. So for right now just trust me, you want your shutter speed to be one 200th of a second. About that. For on this camera it's 1/200 of a second. I will explain that in a future section of this class in great detail. So right now just trust me, 200th of a second then we need to control our aperture value. What should it be? Should it be of eight of 10 F. 16. Well I'm looking on the back of my camera, I've got a little meter here and I can see that pretty much anything over F. Four. My images under exposed so much that it will just show up as black. So I'm gonna set my camera to F. nine and then Teresa look right at me, I'm gonna take a picture again and now look what happens. We're gonna throw that into lightroom 1 2/100 of a second out of nine I. S. 0. 200. It's black in other words at those settings the ambient light is so underexposed it realistically just doesn't exist. We've eliminated the ambient light. Okay so now that we know that if we have no flash on our camera at these settings we have a completely black photo. So now what I'm gonna do, I'm gonna put this speed light on the camera and turn it on. This flash is in T. T. L. Mode. In other words full auto. I am not telling it to do anything. I'm just it's just automatically going to adjust. And so let me just take a photo again. 321. Here we go. Yeah bam So I took a picture here of Theresa notice that my camera settings are exactly the same. 2/ of a second. F. Nine I. S. 0. 100. And if we put these side by side you'll see that the one on the left is almost completely black. There's a little ghost there. The one on the right, we have a Teresa. And so that's how that works. The flash is illuminating our scene. So all the light that we're seeing in this image is coming from this flash. So how can we control this exposure? How can we make the flash brighter or dimmer? How do we control the flash exposure? Well first, um since we're gonna be shooting a lot of stuff here with the flash and auto mode, we need to understand how auto mode works. How does the camera figure out what the proper exposure should be? How does it know if it's too bright or too dark? We'll all have to do with a thing called middle gray. So I have this fancy card here. I'm going to come forward. And so this has this is a uh an X. Right calibrated card exposure card and it has black, middle gray and white. And so when you have a proper exposure this should be black, not dark gray, this should be white, not light gray. And this should be a middle grade sort of in between those two what our camera does and the camera looks at everything in a scene. It looks at the background, the foreground, the subject everything. And it basically puts it in a metaphorical blender. It blends all of those different values together and it wants it to come out as a middle gray. That's what our camera expects it expects for all the different values that you have to be mixed up and come out as a middle gray when everything is averaged out, that works out most of the time. But when we're using speed lights and are shaping light and we're only illuminating little parts of a scene that can cause big problems. And so I want to explain to you how the camera figures out what middle gray is, how the exposure works and do a little crazy demo with a black and white wall. So the first thing I want to do is show you how the camera's flash figures out exposure. It does that was something called a pre flash. And so here is how the pre flash works. This happens so quickly that uh normally you don't even see this happen, it looks like one thing is happening, but really two things are happening. So here's what happens in slow motion. We're gonna slow things down. So when you press the shutter release on your camera, when you have a flash on the camera, what happens is the flash fires and it makes it's called a pre flash. So this flash fires the light comes over to your subject, it reflects off the subject and it bounces back and it goes through the lens. That's where T. T. L. Comes from. The light is coming from here, off the subject through the lens and then the camera takes that exposure and it figures out, okay now I know how much light the flash should give off based on how much light was reflected from the pre flash. It does all those calculations. Then the flash fires again a second time at the correct amount, the correct brightness that flash fires illuminates the subject comes in and makes an exposure. And so you might see occasionally on youtube or the video. When somebody's shooting with a camera with a flash on it, you might see what looks like two flashes because there are two flashes but it happens so fast. We normally don't see it. In fact, I'm gonna point the camera at you. I'm gonna take a picture really fast and I don't think you can see maybe you can see two flashes but it actually happened. There were two flashes again, push the shutter, release the first flash. The pre flash comes out, goes through the lens. The camera figures out what the proper exposure should be. Then the flash fires again eliminates the subject and comes back. So how does the camera figure out what the flash power should be? Well, it's looking for middle gray. It's looking at the scene and it's saying, okay, this should average out to middle grade that causes problems. So what I want to show you Theresa, I'm gonna have you come over here and I'm gonna show you guys this wall over here. So we're gonna move this camera, This camera in here, We have a black and white wall. Now this black is a little bit reflective. So it's not going to do exactly what we want to do but it's black enough and this is white. It's not absolute white but it's white enough. I'm gonna show you what happens when we start mixing these two things together. So what I'm gonna do is I'm gonna come over here and I'm gonna take shots of this and then we're also we have a different camera angle here, we can sort of show you what this works like. So the first thing I'm gonna do is I'm going to take a picture of just this white wall. So just the white wall. So I'm coming over here, I've got my flash set to auto mode and I have filled the frame with just the white wall. Gonna take a shot and my camera, I've put it on manual focus because it cannot focus on that. There we go. Okay, so just the white wall bam. Now when we put this in lightroom this is going to come into lightroom. Remember this is supposed to be a white wall. What is it? It's a gray wall. This wall here. When you put it in lightroom you can see on the hist a gram. It's completely gray. That is, it should be white. But it's great. Now watch what happens when I go back to this wall, I'm gonna take a picture of just the black section of this wall. Same thing I did before. I'm gonna fill the frame with just black. Here we go, I'm gonna take a photo. This is a little bit reflective. So it won't be exactly right. But if we look at this in our lightroom, it's not completely black. It's black sort of down here where the flash didn't show up but it's grayish. So if I put these side by side you can see that this black, it's a little overexposed and the white is definitely underexposed because it's expecting these two things. It's expecting this white wall to be gray. It's expecting this black wall to be gray. And so for the black wall it's over exposing and for the white wall it's under exposing because our camera is expecting things to be middle gray. The camera isn't smart enough to know what we're shooting, it just knows what has been told which is things should average out to middle grade. Watch what happens if I shoot these two things side by side. So now what I'm gonna do is I'm gonna come over here, I'm gonna take a photo of both of these walls at the same time. Now watch what happens when we go in. I guess I should focus that. So let me let me focus this really fast and do that again. Okay that's better. Okay there we go. So now when this comes in here it is bam notice the black is black and the white is white because when we mix those two things together, it averages out to middle grade. So take a look again at this photo and look on the hist a gram here, we have blacks over here, we have whites over here, that's a proper exposure. And so the point of this is the camera doesn't know what we're shooting. It's expecting things to average out to middle gray. It will get it wrong from time to time. So how do we fix that? Well, we fix that with a camera control. Flash control called flash exposure compensation. So remember what we're using now to illuminate our subject is just the light from the flash. So when we're doing any kind of exposure, it's the flash power that we're adjusting. We're increasing the power of the flash or decreasing the power of the flash or we're changing the aperture which we'll get to a little bit, but it's the flash that we're controlling. We don't care about the ambient light anymore. So that's why exposure compensation won't work. We need to use flash exposure compensation. So let me show you how that works. So we have a close up zone that we're gonna be using here, get my little tripod out of the way here. And so what I'm going to show you here, I'm gonna move my camera over here to this little tripod. That's all good. I'm an old man now. So I have to use glasses to see what I'm doing. So we have this flash here and so on. This flash, there's a little button here that I can push and when I push this button it gives me a plus or minus and I can roll this up or roll this down so that gives me flash exposure compensation. In other words, if I want this to be over exposed by a stop, I roll this up so I have to push this little button here, I guess I gotta put my glasses on again to see this. So I have to roll this up to say overexposed by a stop or roll this down to stay under exposed by a stop. So in the case of our white wall we would say take what you think is correct and overexpose it by a stop. What you think should be gray should be white. So take that gray overexpose it by a stop. So let's try that. So I have my flash exposure compensation set to plus one. I'm gonna go over here, I'm gonna focus up on this white wall. Take a photo of that and then we'll show you this on our uh lightroom and you can see here in lightroom that it has worked correctly. So we have this wall that's almost completely white but not white. It is where it should be, compare that to the first photo is shot. So that first photo is gray, the second photo is white. You can see the difference between these two photos, both of these are the white wall. The second one. I use flash exposure compensation. The first one I just let it do its own thing. Let's try the same thing with the black wall. So the blackwall. Remember it expects the black wall to be gray but the black wall was actually uh expects it to be great but it should be black. So I'm gonna go in here, hit this, take my flash exposure compensation down by a stop. Okay, I've got that. Now let's go take a picture of this black wall. So I come back over here. I will focus this up, set this on the black wall, take a photo and now when we come over here we'll look at this in lightroom there it is. So in lightroom you can see that is now black as it should be. So our flash exposure compensation works just great. Okay, so now what we're going to do, I'm gonna move my camera here and we're gonna go back over and we have Theresa come on out and now what we're going to do is we're going to do um some flash exposure compensations with the flash on the camera. It's pretty cool. Okay so here's what we're gonna do. Never flash it's on the camera itself and you can sort of see how this works. Eventually we're gonna get the flash off the camera. So you can see a little bit more how this works. But let's have you back up almost to that white wall, keep going on back. Okay, so right now I have my flash exposure compensation set at zero, you know, I'll just take a shot of Teresa and this should be pretty good. But this shot when we look at it, you can see that Teresa is a little bit underexposed, you can see that this white over here is not quite white were under exposed a little bit because again, we have all of this white around Teresa fooling the camera into thinking that things should be a little bit great. So all I'm gonna do is I'm gonna take this, Change my flash exposure compensation up to about plus three stops plus .07. And then I'm gonna zoom in on Teresa again, take a photo. And now when we look at this next shot here, notice how the white on the hist, a gram jumped over. So if I go back, see the white over here on the history RAM is down. If I go over here, it's up. So we're using our flash exposure compensation to change how everything works. And so we're gonna be doing all of that as we go forward. You'll see me using flash exposure compensation when we're in auto mode to change how our camera and our flash work together to get a correct exposure. Now there is definitely a better way of getting your exposure correct by shooting with a light meter and total manual mode. We are going to get to that, but first I want to explain to you and make you have a solid foundation for using flash exposure compensation because a lot of times that's all you need. So the next thing we're going to do is I'm going to show you that you don't have to get the flash off the camera all the time to get great portraits. I'm gonna take a little challenge and see if I can create a great portrait of you with a flash on camera. And then we're gonna start moving things off the camera and doing metering and all that kind of stuff. So we're gonna do a little portrait in the next session.