Silly Camera Numbers

[by Gheorghe Chistol]

There are lots of numbers on cameras and that gets people scared and they get confused over what is an Fstop, Shutter Speed and ISO and this silly number confusion prevents you from taking good photos.

How Much Light is Enough?

As you know you need just enough light to take a good photo. The amount of light can vary a lot throughout the day. That's why you want to have some control over the settings of your camera. The "Fun Saver" film cameras so popular throughout the nineties have a single setting, which is why sometimes half the photos on a roll of "Fun Saver" film do not look very good.

You can use the aperture of your lens and the shutter speed of your camera to control the amount of light. The lens has a diaphragm that forms a "hole" through which light passes. The smaller the aperture, the less light passes through the lens. The Fstop is a number which quantifies the opening of the aperture. Full stop numbers are f/1.8, f/2.8, f/4/0, f/5.6, f/8.0, f/11, f/16, f/22, f/32, f/64. They are called "full stops" because when you change the aperture from f/11 to f/8.0 that doubles the amount of light. Every time you go up one stop f/5.6 -> f/4.0, you double the amount of light that gets through the lens. People usually say "stop down one" if they mean to decrease the aperture (hole) by a full stop (f/2.8 -> f/4.0). There are other intermediate fstop numbers on your lens, but the idea is the same.

The shutter speed is a number that tells you how much time the film (or digital sensor) is exposed to light that goes through the lens. In every camera, there is a shutter between the lens and the film/sensor which acts like a very fast curtain and opens very fast for a fraction of a second. Suppose you need to expose the film for a 1/60th of a second. You can call this shutter speed 60th. If you need to expose the film for 1/200th of a second, you call that shutter speed 200th, and so on.

Take it From Here

Ok, you got the Fstop and the Shutter Speed. Suppose you need a total amount of light X to get a good photo. Your light meter (either built in the camera or handheld) tells you that for a properly exposed photo you need to set the camera to shutter speed S and fstop F. Here is an example:

Good Photo: S=1/400 (shutter speed 1/400sec) and f/2.8 (Fstop)
Equally Good Photo in identical conditions: S=1/200 and f/4.0
Equally Good Photo: S=1/100 and f/5.6
Equally Good Photo: S=1/50 and f/8.0

When I say "equally good" I mean that you get the same amount of light, just enough to properly expose the film. What is the difference between all these settings then? The difference here is depth of field (DOF). Suppose you focus on a person's face. If the background is very blurry, you say that the lens has a shallow depth of field. If you see obsects in the background clearly, then you can say that the lens has a big depth of field. You can understand DOF concept a lot easier by looking at this series of photos (five lovely ETs). The photos were taken in identical lighting with manual settings (see the Fstop and Shutter Speed and make sure that the amount of light stays the same for every photo). See how the DOF changes when the Fstop changes. In every photo I focused on the face of the first ET.

f/2.8 Shutter: 1/400sec

f/4.0 Shutter: 1/200sec

f/5.6 Shutter: 1/100sec

f/8.0 Shutter: 1/50sec

f/11 Shutter: 1/25sec

f/16 Shutter: 1/13sec

f/22 Shutter: 1/6sec

You can see that at f/2.8 the DOF is very shallow, only the face of the first ET is in focus, every thing else is blurred. You can't distinguish anything in the background. With f/22, all ETs are fairly sharp (big DOF) and you can even see the pattern of the background objects.

Acceptable Shutter Speeds

Shutter speeds can range from seconds to thousands of a second. Humans are not very good at holding still, that's why you can't take a good hand-held photo if you have a shutter speed of 1/5sec. While your film is being exposed for one 15th of a second in the camera, your hand may move significantly and you will get an unintended blurry photo (even though you focused on an object, that object is not sharp in the photo). Please remember the inverse rule: the slowest reasonable shutter speed equals the focal length of your lens. Suppose you are using a 50mm lens (normal lens, quite useful and handy), then the slowest acceptable shutter speed is about 1/50sec. That is if you are not using a tripod. With a tripod you can get sharp photos even if your shutter speed is several seconds.

When Do You Use What Settings

A good photograph has no recipe, it's a matter of taste. But you can control your camera and make it do what you want. You might want to use wide open apertures (f/1.8, f/2.8) for portraits because the background will be blurred and it will look nice. Wide apertures come in handy when you shoot indoors and there is little light (the wider the aperture, the more light you get through the lens, the faster the shutter speed you can use and the less the likelihood that you will get blurry photos).

You might want to "stop down" (i.e. use smaller apertures like f/8 and f/11) for architecture shots and for shooting large crowds of people when you want all of them to be sharp (also for shooting landscapes, like Ansel Adams).

Post Scriptum

Don't take my words for given, go out and take photos and try things out. See how a blurry photo looks like when you shoot at shutter speed 1/10, or how an underexposed photo looks like when you've got little light. Try shooting portraits with shallow DOF and with deep Depth of Field. Shoot buildings, landscapes (if you can find those around MIT), people. Shoot people from far away, from close and very close distances. Shoot auto-portraits of yourself in the mirror, make crazy faces and ask your friends to do the same. There is nothing that limits what you can do.

Good luck with your work


PPS: here are some photos shot by Technique staff, they were all printed in our darkroom. Of course they are not perfect, but you will never achieve perfection. Most of these photos was taken by our beginner staff members who just showed up, asked for a camera and started taking photos right away.