Lesson 3 - Aperture and Shutter Speed

I've been bad with updating my blogs... But the good thing is, I have some more free time now, so I have more time to update my blogs... stick me on this one and you WILL learn all about photography...

Shutter speed and apertures work together to ensure that the correct amount of light falls onto the SENSOR. In other words, your camera, through its automatic exposure settings, will make all these decisions for you. However, for you to intelligently use these automated functions, you need to understand what they mean and how they are inter-dependent, so here’s a brief overview of the relationship between shutter speeds and aperture settings:

Apertures
This refers to the variable-sized hole in the center of your lens with which you control the amount of light falling onto the sensor.

Since the start of photography, camera manufacturers have indicated the size of these apertures by using the term "f-stops". All lenses had the following standard f-stops, f1.8, f2, f2.8, f4, f5.6, f8, f11, f16 and f22 – f1.8 being "wide open" or a large aperture, and f22 being "closed down", or a small aperture.

Each stop allows twice as much light onto your sensor as the next stop due to the quadratic relationship between diameter and the area of aperture (which you don’t have to remember!), so f4 would allow twice as much light through as f5.6.
By setting a large aperture on your lens (around f2 or f4) you allow a large amount of light through onto the sensor.

Setting a large aperture also:
1. throws the background out of focus (ideal for portraiture), and
2. forces a higher shutter speed to compensate for the amount of light and to freeze the action.
If light is in abundance, you’re likely to select a small aperture (around f16), allowing only a speck of light through.

Setting a small aperture also:
1. makes both the foreground and background pin-sharp but
2. forces a low shutter speed, which could induce camera shake.
In photographic terms we talk about "closing down a stop", meaning that if the light is too bright and your image is over-exposed (by one stop), you should close the aperture by one stop to halve the light falling onto the sensor. If you were shooting at an aperture setting of f11, for instance, you would then change it to f16 (smaller, therefore less light comes through).

You can find these apertures – or the electronic versions thereof – by setting the camera to manual exposure mode. You will also note that while the camera shows the "classic" apertures of f4, f5.6 and so forth, it also shows "half stops" of f5 for finer adjustments to your exposure.

Shutter speed
A shutter is, in simple terms, a black curtain with a square opening in it situated between your lens and the sensor behind it. When you press the shutter release, the curtain zips across the sensor in a wink of an eye, allowing light through the hole and onto the sensor. We measure the speed with which it zips across the sensor in parts of a second, again a relic of the earliest times of photography. Some of these units are 1/8th of a second, a 16th, a 25th, a 60th, a 125th, and so on all the way up to an 8000th of a second and down to 30 seconds, on some cameras.

Each shutter speed is roughly half the duration of the next, just like apertures. In other words, a shutter fired at a 250th would whip past the sensor at double the speed than if set to a 125th. It follows then that it being open for only half the time, it would only allow half the light through onto the sensor. Again, modern camera manufacturers have added an in-between shutter speed to fine-tune exposures, as you will see on your camera if you set it to manual exposure.

Why should you know all this? Aperture and shutter speeds are inextricably linked. Try and understand it by using this analogy: let’s say that if you poured water through a pipe one cm in diameter for one minute, you will have one liter of water in the bucket below. If, however, your pipe is half a cm in diameter, and you still want one liter of water in the bucket, you will have to pour for double the length of time – 2 minutes.

Conversely, if you used a cm-wide pipe but only wanted half a liter of water in the bucket, you should only pour for 30 seconds. That inverse relationship is the same in photography: your pipe’s diameter is nothing but the aperture, and the duration of pouring is the duration of exposure. Now take this slightly further – if you want to fill a one-liter bucket to the brim, that filled bucket is a properly exposed image. Too much water, and it overflows (overexposes), and vice versa.

That is the inverse relationship between aperture and shutter speed, one that your camera takes care of automatically if you’re shooting in the auto exposure modes (TV, AV or S and A).

So why would you need to know how the relationship works? Let’s take a practical example: say you want to take a picture of a stream of water and to make the water look like a white, continuous stream of foam, almost like a bridal veil.

The only way in which you can get it to look like that is to shoot at such a slow shutter speed that the water becomes blurred into that wonderfully white stream. So you have to force the camera to select a slow enough shutter speed.

So now you have to play around with these settings and put the theory into practice.. Now.. go play! and check back next week for lesson 4