Seems like an odd title to an article, right? Well, it’s true! If you’ve ever thought about making the switch to exposing fully manually, but struggled to get apertures and shutter speeds to do what you want them to do, all you need to do is to remember that your camera is just like a faucet.
Suppose you are thirsty and have a glass of water you’d like to fill up. When you turn your faucet on just a little bit, it takes a long time to fill up as it trickles in. If you’re in a hurry, what do you do? You twist the knob all the way open so the water comes out in a larger stream and it only takes a short time to fill up.
This is exactly the relationship between the aperture and the shutter speed. When you only let in a little bit of light to your camera’s sensor, you have to let it hit the sensor longer, with a slower shutter speed, to expose the image properly. If you blast the sensor with a lot of light, it needs just a short time to hit the sensor and expose the image properly.
The only tricky part here is to remember that a small “volume” of light does not mean a smaller aperture number (like f2.8 or f4), it actually means a higher number (like f16, or f32). A lot of manuals don’t explain this clearly, but I was taught this in college and it made everything click for me; the f-stop number represents the amount of times the opening of the aperture can fit between the front of the lens and the back. Imagine 4 equally sized circles, end to end, from the front of your lens, to the back. Now imagine 16 of them. The 16 equally sized circles are going to be much smaller than the four equally sized circles to cover the same distance. That is why f16 lets in less light (less “water into the cup” if you will, and requires more time (shutter speed) to “fill the cup” (your photo) than shooting at f4 does!
Now, you have an easy way of remembering just what you need to know when you make the switch from shooting programmed or partially programmed, to manual!