Tag Archives: lens

July 13, 2007 · 4:08 pm

Three things that go into exposure

Too Bright As we learned before, when you take a picture a few things happen quickly. First, the aperture closes to block some of the light that’s coming into the camera. Second, the shutter opens and closes. As soon as that happens, the magic gnomes on the camera’s sensor record whatever light they saw when the shutter was open.

I’m sure you’ve taken some pictures that came out way too dark, or maybe even completely black. You’ve probably also taken some that were really light and washed out. We call those dark pictures underexposed, since they didn’t get enough light. The way too light ones are called… can you guess? That’s right, overexposed! Give yourself a shiny gold star.

You’ll see three little bears next to the text in this article. The first one is too bright– he’s overexposed. The second one is too dark– she’s underexposed. Baby bear is at the bottom– he’s juuuuuuusssttt right. IF you go through all of the lessons on this site and do all of the exercises, you’ll know what it takes to get all of your pictures to be just like baby bear.

Too Dark There are three basic things that go into the equation for how a picture will be exposed. The first is how long the shutter is open– if it’s open for a long time, a lot of light gets in and lands on the sensor. If it’s only open for a very short period of time, a lot less gets in. Because photographers like fancy schmancy terms, we call this shutter speed.

The second thing that controls exposure is how big the aperture is. If it’s closed down so that there’s only a tiny hole, not much light gets in. If it’s wide open, a lot more light comes in and lands on the sensor.

If you can’t make sense of how aperture works, imagine that you’re in a plain room with no lights at all… not even the glow of a computer screen. (Stop shaking… it’s an imaginary room.) All of the light in this room comes from one window that faces out to a bright sunny day. If the room has a really big window, then the room will be bright and sunny. On the other hand, if it has a teeny tiny window, the room will be pretty dark. The aperture on your camera is like the only window the camera has. If the aperture is big, lots of light gets in. If it’s small, only a little bit of light sneaks through.

Just Right The third thing that goes into exposure is called ISO, and it’s a measure of how sensitive the sensor is. Remember our sensor gnomes? Think of them as light microphones. If the camera is set to a very high ISO (e.g. 800 or higher), the gnomes will be able to record small amounts of light. At low ISOs (100, 200) the gnomes need a lot of light.

Right about now, you’re probably thinking that you want the gnomes to be as sensitive as possible, but that’s not true. For now, just trust me on this, and I’ll explain later.

Next lesson:  Shutter speed, how it works

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July 12, 2007 · 9:47 am

How your camera works, in overly simplified terms

In order to understand photography, you need to have a basic understanding of how your camera works. Don’t get scared! Even a six-year-old could understand this. In fact, here’s what your camera might look like if a six-year-old used Paint to draw it:
A six-year-old's view of your camera

At the very back of the camera there’s a sensor that records whatever light hits it. We don’t really care much about how this happens right now, since it doesn’t matter. For our purposes, let’s pretend that there are millions of magic camera gnomes that live on the sensor rubbing shoulders with each other and spend all their time waiting for a little bit of light to reach them. When they see light, they get excited and record exactly how much light they see.

If the gnomes always got light they’d get tired and stop working, so right in front of the camera is a shutter. Think of this as a curtain that’s closed almost all of the time, but opens up for a brief moment when you want to take a picture.

Whenever we take a picture there’s a lens attached to the front of the camera, and that’s where the light comes in. The lens has a lot of glass in it arranged in special ways so that everything focuses just so, but we can treat this as magic too. In addition to the glass, there’s a round opening called the aperture or diaphragm. The diaphragm controls how much light gets into the camera– open wide and a lot gets in. If it closes down to a tiny pinhole, only a little bit of light gets through to the gnomes. When you aren’t taking a picture the diaphragm is always open as far as it can be, and when you take a picture it closes down to let the right amount of light in.

When you take a picture, a few things happen really quickly: the diaphragm squeezes down to block out some of the light, the shutter curtain goes up very quickly, the gnomes get all excited and write down what they see, and then the curtain closes and the gnomes go back to waiting.

And that’s it in a nutshell– the magic of photography. In the next few lessons, we’ll learn how to control the aperture, the shutter, and the elves in order to take good pictures.

Next lesson: The three things that go into exposure.

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