The problem is, When you depress the shutter, all three of these things are determined at the same time and place if you are just shooting normally. When you depress the shutter your camera exposes whatever is in the center of your frame and focuses on whatever is closest usually if you are using default settings. That means in a scene where the closest thing to you is not what you wanted to focus on, you miss focus. Or in a scene where the center of the image is not what you want to be exposed correctly, you miss exposure. If you adjust your camera to expose that different part of the image, you just changed your composition. But there is an easy way to fix this. What I will try to explain in this tutorial is a three step process to making sure all elements in a picture are how you want them without having to manually focus and manually expose. Sure, you can just manually focus and manually expose every image you take, but that takes a long time and in a lot of situations is not the best way to do things. Some people will tell you to focus-recompose, but that doesn't take into account exposure. You should address all three. First you lock exposure. Then you set your focus. then you compose. THEN you take the picture. Let's get started. I will use all weird shots from Philly (why not) to explain this.
First, put your camera in center point AF. This can only be done in P, TV, AV, or M modes. You should be shooting in one of these modes anyway. I have a 5DMKII and 30D (Canon) so I will you show you on my 30D. If you have a Nikon, these things are basically the same on both cameras, get out your manual and try to follow along by cross referencing. It's raining and I don't feel like setting up off camera strobes and what not, so we are gonna be shooting with the good low light one. The 30D has probably the worst low light performance of any camera, but since it came out in 1922 I'll forgive it. Anyway, this is what you need to use- These two buttons.
The button on the right with the plus sign inside of the box is what lets you set the AF point. Scroll with the wheel until the red light illuminates the center point. If you have another camera, it's basically the same thing, you look up how to change your AF point and scroll till you have selected the center point. Now you are ready to begin the process. I just found another light, so this picture is of my 5DMKII and is of which AF point I use.
You see the button with the asterisk? That is your Exposure Lock Button (AE Lock). Instead of metering on where you focus, this lets you set a different point. What's metering you ask? It's how your camera tries to make the image look like it does in real life by measuring reflected light. It tries to make an image match "middle grey", this is a grey that reflects 10-18% of light. It's like halfway between white and black on grey or any other color. This is why if you meter on snow it looks darker, it tries to make it a middle grey. Or when you meter on something darker, it tries to make it lighter. This could be a whole another tutorial in itself. Anyway hitting this button locks the exposure in the camera until you take a picture (or a certain amount of time has passed but nothing you should be worried with) usually this happens when you press the shutter button halfway. You use this button if the thing you want to meter (expose for) is different than the thing you want the focus to be on. This takes some getting used to and experience helps. If you have a bright part of the image and a dark part, try to meter on the spot between them to get a good average. Or if one part is more important, meter on that. This helps with people who are backlit, I meter on an area of their body that is not silhouetted against the sun, like maybe their waist or feet if it is below the horizon.
Once you have locked your exposure for the image, you then identify what you want in focus. You point your center AF point on that object and depress your shutter button halfway and keep your finger on it. this just locked in your exposure. You can now move your viewfinder to compose your image anyway you please, with your exposure and focus set independently of your composition. depress the shutter completely and you now have a well thought out image. Here is an example.
Notice I exposed and focused for the pole in the first image in the same spot but it was too bright. I then metered for the background in the next image but kept focus on the pole.
The way I kept focus on the pole was I aimed the center AF point on the right side of the background and hit the AE Lock button. This locked exposure. I then depressed my shutter halfway on the middle of the pole, which locked my focus on the middle of the pole. I then kept my finger halfway pressed down on the shutter and adjusted my viewfinder until it was in between the background and focus point. This is not going to be hanging in any museums any time soon, but it illustrates this point very well. You see now you have the ability to creatively compose your image on the fly without wondering why the image looks off or is not in focus. If you try and follow the rule of thirds, you have to use this or all of your subjects will be dead center and boring.
There are more many more things to go over with this technique but it would take a long time and involve me actually speaking to you and showing you real scenes. A few pointers though to help you along: You need to not re-compose up or down to far if your subject is close or you will miss your focus. Side to side movement is fine. You also need to be wary of what metering more you are in. I use evaluative metering more most of the time, so when I AE Lock, I don't do it directly on the spot I want exposed for. I just nudge it closer to that spot than the area I don't want to expose for. If you use Spot metering, just plop it right on the area you want to expose for and you are golden. Make sure you are in the right auto focus mode also. You should be in one-shot AF mode, if you are in AI Servo mode your focus will change as soon as you recompose. These things come with experience, so go out and shoot! You should aim to be able to do anything on your camera without looking at it. If you can't...figure it out. Many a shot will be missed until you can. It's fun to shoot around and get good images by accident (How I did it for a long, long time) or through a little knowledge, or maybe pushing things with photo software, but if you make the jump into being a professional and are being paid to do something and you are presented with a situation you do not know how to handle... you look like an idiot and there is no excuse.
Read your manual.
