The 30-Second Photography Lecture*
*Ok, it's really more like two – three minutes. 30 Seconds makes a better title.
Taking pictures is easy. Point the camera at something and push the button, right? Well, with today's cameras it often is that easy. They're little full-auto wizards that do their best to give you a usable picture.
But what if you don't want 'usable'? What if you want 'really good' or maybe even 'great'? Or what if you're trying to get a picture in a situation the little auto-wizards don't do well with, like a closeup of something shiny? That's when you need to know some things about photography.
Ok, so on to the basics. We're going to talk about film even though these days it's more likely to be a digital sensor. The basics are still the same.
So, in order to take a picture you need to get a certain amount of light on to the film. It helps if that light is a nicely focused image of what you wanted to take a picture of, but for now that's optional. We're going to call that amount of light you need for a picture one gallon of light. Pour half a gallon on the film and your picture is too dark. Pour two gallons and it's too light. Somehow the camera manages to control things to get that one gallon. How does it do it?
There are two things the camera can change to control how much light gets to the film. Don't worry about types of film or the ISO speed setting on your digital for now – those just change how much light makes up that 'gallon'. All you really have for controls are the shutter speed and aperature.
The Shutter Speed is just that – how fast the shutter opens and closes. This controls how long the flow of light goes on for. It's usually expressed as a fraction of a second so if the shutter is going to be open for 1/30th of a second it will show '30'. If it was going to be open for 30 seconds most cameras would show '30s'.
The Aperature relates to your lens. There's an adjustable plate inside your lens that can be open all the way or it can be closed down to a little pinhole. Aperature is expressed in f-stops, sometimes just called 'stops'. They're a fraction of the wide open aperature so the bigger the number the smaller the hole it represents. Because they're fractions of the area of a circle they're odd looking numbers. A wide open, can't get any bigger aperature would be a 1 because 1/1 of something is all of it. The next full stop down from there is having the aperature half way open. You'd think that would be ½ or 'f2' but no – remember that we're dealing with the area of a circle so it's actually f1.4. The stop after that is f2. All you need to remember to figure out the whole stops are those two numbers, 1.4 and 2. Every other full aperature stop is a multiple of them. They alternate so the sequence goes: 1, 1.4, 2, 2.8, 4, 5.6, 8, 11*, 16, 22, 32... Wait a minute – 11? That's not twice 5.6! No it isn't but let's face it – 11 is close enough and the math is complicated enough all ready.
Alright then, so how does this all relate to controlling things to getting that perfect one gallon of light? Well, think of your lens as a funnel. When you pour water through a funnel the bigger the hole in the funnel is the faster the water (or light) pours through. If you have a funnel with a 6 inch wide opening you can pour a gallon of water through it really fast. If the hole is only 1/10th of an inch then that gallon's going to take a while. Same with your lens – the wider the aperature (the more the lens is open) the more light that goes through it in a certain time.
I mentioned that aperatures are all one half of or twice the adjacent 'full stops'. Shutter speeds are the same way, once again with an occasional adjustment to an easier number. A typical series of speeds would be: 1s, ½ (usually just '2'), ¼ (4), 1/8 (8), 15 (making life easier later), 30, 60, 120, 250 (another skip to an easier number), 500, 1000....
Now the fun thing about the relationship between shutter speeds and aperatures is that they work together. If a setting of 1/60th at f8 gives you your 'gallon' of light then so will any pair of settings that are the right set of adjustments from there. If you keep the shutter open twice as long (1/30th) then if you cut the aperature in half (f11) you'll get the same amount of light. So 60 f8 == 30 f11 == 120 f5.6 == 15 f16 ==.....
Ok, so now you know how to adjust your shutter speed and aperature to get the same amount of light at different sets of settings. Why would you want to do that?
Sometimes you have to. If it's a bit dark you need to either open the lens (aperature) up more or leave the shutter open longer. Most lenses have a maximum aperature that they can't open past. That means you have to leave the shutter open longer. But if you leave the shutter open longer things can blur if they move or you do. So sometimes you want to open the lens up more so you can shorten the shutter time (increase the shutter speed).
Sometimes you just want to. Leaving the shutter open longer makes moving things blur. Like water. Set your camera on a tripod and adjust to a shutter speed of at least 1/30th or longer and moving water will get that smooth and silky look.
Now that we know how to get the same amount of light at different settings, what do you do if you want things brighter or darker?
That's pretty simple too. To make things brighter you need to add light so you either open your aperature up or increase your shutter speed. To make them darker you need to subtract light so you close your aperature or decrease your shutter speed.
Here's another reason to adjust your settings. It's something called “Depth of Field” or DOF. What it refers to is how much of your picture is in focus. We're going to seem to wander off a bit but stick with me, this will all make sense in the end.
When you focus your lens the light is supposed to be coming to a nice, sharp point right on the film. Actually, it doesn't have to be quite a perfect point. The grains in the film / pixels in the sensor are only so small, plus there's a thing called the “Circle of Confusion” which relates to the smallest size spot your eye can distinguish. Anything smaller than that is a point as far as you can tell. And what that means is that you can be a little bit away from that perfect, sharply focused point and still look like you're there.
Let's think about that cone of light coming through your lens. One important bit is that after they come to that perfect point the light rays are going to start spreading out on the other side making a cone shape that matches the one coming from the lens. The next bit is to think about the fact that you don't have to be right at the point to be in focus. That means that things that are a little bit out of 'perfect' focus are still going to look like they're perfectly focused both in front of and behind your focal point.
We're going to shoot back up to the aperature for a second. Remember that if you open your aperature up wider you get more light, right? Well you also get a bigger hole for the light to come through which means that the 'cones' you're making are big fat ones. You don't have to go very far from the point of a big, fat cone for the cross section to get fat and exceed your Circle of Confusion. That means that the wider your aperature is, the narrower your DOF is. But if you close down your aperature you get a small hole and a really skinny cone and now you can go quite a ways from the point and still have a small enough circle.
So, if you want to isolate just what you're focused on (say, someone's face) you focus on their eyes (if the eyes are in focus the picture looks like it's in focus) and use the widest aperature you can (say f2.8). But if you want to get a picture of a group (or an object) and what as much in focus as possible then you want to close down your aperature as far as you can (f22).
All right then! Now you know that the Aperature is literally referring to the hole the camera looks through, the Shutter Speed is just how fast the shutter opens and closes, and that bigger holes mean shallower pictures and narrow holes mean deeper pictures. You also know that wider holes mean faster pictures and narrow holes mean longer pictures. And that if you change one setting one direction you can change the other setting the same amount in the other direction to get the same amount of light.
Now get out a digital camera and do some experiments! You'll be amazed at what you can do with just this little bit of information.
Oh – and one last thing: The secret to better, sharper pictures.
Use a tripod.
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