Sunday, January 30, 2011

What all the damn numbers on your camera mean

I encourage all of my friends to take up film photography, so to help them out of the trouble I have gotten them into, I'll be posting a little series of pieces about my methods. I like to do things about as easy, quick and dirty as is possible, so hopefully this will all be easier to understand and use than when it's explained by photo geeks with delusions of being the second coming of Ansel Adams on steroids and crack.

Before I can tell you what all the damn numbers mean, you need to understand what is actually happening when you press the little button to take a picture.

Exposure: what it is. 
It's how much light you let hit the film when you take a picture. There are three factors that go into your exposure: shutter speed, film speed, and aperture.

Shutter speed = how long the camera shutter stays open to let in light.
Film speed = how sensitive your film is to light.
Aperture = the size of the opening the light comes through.

A fourth factor is the brightness of the light coming through the lens. For now we'll assume that's part of the terrain and you can't do anything about it. Film speed is also sort of a given, because unless you're some kind of freak, you are not going to change film to get a single shot. So the main settings you have to work with creatively are shutter speed and aperture.

 Shutter speed:
Fast shutter = freezes action; requires wider aperture and/or brighter light.
Slow shutter = allows creative motion blurring; necessary in low light/small apertures.

 Controls depth of field: how in focus close and distant things are, in addition to the thing you're focusing on.

Small aperture = deeper range of focus
Large aperture = shallower range of focus

Aperture is also called f-stop, and each "stop" has a number assigned to it- 1.8, 2.8, 4, 5.6, 8, 11, 16
High numbers = small aperture
Low numbers = large aperture

High number/small aperture/greater depth of field requires a longer exposure.
Low number/large aperture/shallow depth of field requires/allows a faster exposure.

 When you take a picture with your camera in program/automatic mode, the camera:
1. Takes a light meter reading of whatever you are pointing the camera at.
2. Decides on an aperture and shutter speed for the shot, based on that meter reading and the speed of the film.
3. Fires the shutter to actually take the picture.

The numbers. Get to the damn numbers.
The entire reason you're reading this is that there are a bunch of numbers printed on your camera and on the film boxes and you don't know what they mean and you are scared. Numbers like:

Shutter speeds (in fractions of a second): 15, 30, 60, 125, 250, 500, 1000, 2000
Aperture/f-stops: 1.8, 2.8, 4, 5.6, 8, 11, 16
Film speeds: 50, 100, 200, 400, 800, 1600, 3200

The important thing to know is that for all of these, each successive number represents a doubling or halving of the amount of light in question:

- Film: 400 speed film is twice as sensitive to light ("fast") as  200 speed; 200 speed is twice as fast as 100 speed, and so on.

- Shutter speed: Obviously, 1/125 of a second twice as long as 1/250 of a second. Even where the shutter numbers do not exactly double, they are still double for the purposes of photography.

- Aperture: The series of f-stop numbers is based on a complex equation I don't understand; but f5.6 allows twice as much light as f8, which allows twice as much light as f11.

Since each set of numbers is based on doubles, you can compensate for changing one setting by changing another correspondingly. If the camera's meter calls for an exposure of 500, with an aperture of f8, you could get the same correct exposure by going to an exposure of 1000, and the next larger aperture, f5.6. Or you could go the other way, to a shutter speed of 250, and the next smaller aperture, f11.

1/500 @ f8 = 1/1000 @ f5.6 = 1/250 @ f11

When you get a decent flash unit and decide to learn how to use it, the same rule applies- the flash can fire at full power, half power, quarter power, etc.

The reason for choosing one pair of settings over another could be if the subject was moving fast, and you want to freeze motion with a fast shutter speed. Or if you want a shallow depth of field with the background and foreground out of focus, you would go to a wider aperture/faster shutter speed. If you want the subject, plus a dog in the foreground and a fire engine in the distance to all be in focus, you would go to a smaller aperture and a slower shutter speed.

So, again:
small aperture = high DOF = slow shutter speed = potential motion blurring
wide aperture = shallow DOF = faster shutter speed = freezes action

What you are supposed to do with this:
First, stop being afraid of your camera. Then start exercising a little creative control over your pictures. Most modern 35mm SLRs have a range of options- manual, program, aperture priority, and shutter priority. They're extremely easy to use once you understand them.

Manual = you set the shutter speed and aperture based on the camera's light meter. You'll figure out eventually when it's time to use this mode.

Aperture priority = you set the aperture and the camera sets the shutter speed accordingly. Use this when DOF is your main creative concern. You either want everything to be in focus, or you want to creatively blur the background and/or foreground.

Shutter priority = you set the shutter speed and the camera sets the aperture accordingly. Use this when you definitely want to freeze or blur action. 

Program = the camera does everything. Use this if you don't know how to set the other modes, or if you don't know how to change the shutter speed/aperture on your camera, or if the Hindenberg is exploding and you don't have time to think. Learn how to do those other things.

Buh, I see numbers you didn't explain!
You're right, I didn't tell you what some of the things on your lens barrel mean, and probably some other things. For now, you don't need to know that- you're not going to blow any shots because you didn't know how to use the DOF gauge. Just go take some pictures and see how playing with the aperture and shutter speed effect your results.

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