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Exposure – Relation Between Shutter Speed and Aperture Value

Shutter Value

If you open the tap more by turning the faucet, that’s the same as using a SHORTER shutter speed. Let’s say it takes 100 drips to fill the pail, by opening the faucet to 5 drips-per-second, you’ll fill the pail in 20 seconds (5×20=100).

If you increase the flow to 100 drips/sec, then you’ll fill the pail in one second. If you turn down the faucet to 2 drips/sec, you’ll need 50 seconds to fill the same 100-drip amount of the pail.

You’re changing the TIME VALUE it takes to fill the bucket. That’s why Shutter Priority mode in most cameras are called “Tv” or Time Value.

Figure 4 – Increasing Shutter Speed

Aperture Value

Another way to fill up the pail quicker is to increase the flow of the water is to enlarge the faucet’s opening itself. Light is relatively infinite and the more you open the aperture, the more light enters.

Figure 5 – Enlarge Aperture

The larger the spout of the faucet, the less time you need to keep the taps open. Assuming that you’re still flowing the same amount of water, however, the amount of water that’ll end up in the pail will still be the same.

That’s the reason why large aperture lenses allow you to shoot at faster shutter speed than a slow lens, you’re allowing more light through in lesser amount of time.

Increasing Film/Sensor Sensitivity

The last parameter we can change is the pail itself. By making the pail size smaller, we can fill it up a lot faster. The same thing happens when you increase your sensor’s sensitivity or using a fast film.

You allow a lot less time to expose the sensor or film, but at an expense of grain or noise. In terms of the pail, we’re sacrificing the volume of water we can store.

Figure 4: Increase Sensitivity

Figure 6: Increase Sensitivity

Of course, you can combine all three parameter changes and see how it affects your exposure as well.

Figure 6: Increasing Light Flow

Figure 7: Increasing Light Flow

Figure 7: Decrease Settings

Figure 8: Decrease Light Flow

Naturally, Figure 6 will fill up the cup in a jiffy, while Figure 7 will take a lot longer to fill up. If you don’t stop Figure 6 somehow (by stopping the exposure), you’ll overfill the bucket (i.e. OVEREXPOSURE), conversely, if you stop the water flow too soon, you won’t fill the pail at all (i.e. UNDEREXPOSURE).

It’s that simple.

Finally, let’s take a look at some real-world, practical examples on the last page.

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