Photography: The Science of Light

In the word “photography”, “photo” means light. Above and beyond everything else, photography is about light. A really well posed subject with a beautiful background can be destroyed by taking in too much or too little light. Now it is true that a lot of compensation can be done using post production tools such as Photoshop, but a lot of post production time can be saved by taking the picture properly first in the camera. In this blog, we are going to talk about the three components of light control, and how each one of them helps to determine the look and feel of your images.


Take 3

There are three settings in your camera that control the amount of light and the matter in which it comes in. They are the aperture, the shutter speed, and the ISO setting. In any given situation there are many, many combinations of aperture, shutter speed, and ISO that will give you a proper exposure. Generally aperture and shutter speed work together and ISO is used as a type of multiplier. The two most important settings are aperture and shutter speed.

Aperture

Aperture is the size of the lens opening. The bigger the lens opening the more light comes in, and the smaller the lens opening the less light comes in. Back in the old days, the aperture was set on the lens itself. Nowadays it is set electronically in the viewfinder of the camera. But regardless, the end result will be the same. The values of the aperture are called f-stops and go something like this: 1.4, 2, 2.8, 4, 5.6, 8, 11, 16, and 22. In writing they look like this: f4, f5.6, f8. How many of these setting you have will depend on your lens. The more expensive the lens the wider range of values it will have. It is the lower end that will change. Some lenses only go as low as 4, while others as low as 1.4. Comparing apples to apples, the lens with the lower aperture settings will cost you more money because it has a bigger lens opening and can let in more light. Using this example, the smallest value, 1.4, is the biggest lens opening and therefore lets in the most amount of light. The largest setting, 22, is the smallest lens opening and therefore lets in the least amount of light. Each value of the aperture lets in twice as much or half as much light, depending on the direction you are taking. So f5.6 lets in half as the light as f4, f8 lets in half the light as f5.6. Or conversely; f5.6 lets in twice as much light as f8, and f4 lets in twice as much light as f5.6. Think of it as, you have a room full of people who have to get out and there is only one door. One of the factors that can determine how quickly the people can get out will be the size of the door opening. The bigger the door opening the more people can get out at one time, the smaller the door opening the fewer people can get out at one time. It is important to understand that aperture and shutter speed are partners, they work together, and an understanding of how they work together is crucial to the understanding of controlling light and of photography.

Shutter Speed

Shutter speed is, how long the shutter stays open. The longer it stays open the more light comes in, the quicker it closes the less light comes in. The values of the shutter speed go something like this: 1/8, 1/15, 1/30, 1/60, 1/125, 1/250, 1/500, 1/1000, 1/2000, 1/4000. The values are how long the shutter stays open in seconds. So 1/8 means that the shutter stays open an eighth of a second. Like aperture each value lets in half as much or twice as much light as the adjacent setting depending on your direction. Therefore, 1/60 lets in twice as much light as 1/125, and 1/125 lets in twice as much light as 1/250 of a second. Going back to our analogy of a room full of people that need to get out; let’s say that the door is broken and keeps opening and closing, opening and closing. Obviously the longer the door stays open the more people can get out at one time, and the shorter the door stays open the fewer the amount of people can get out at one time.

Now remember I said that aperture and shutter speed work together. When you are adjusting your camera to let in the proper amount of light, you can adjust the aperture (the size of the lens opening), the shutter speed (on long the shutter stays open), or both to control the amount of light that comes in. Think of it like a teeter-totter. Now this analogy will only work if you can remember what a teeter-totter is and how it works. So, you have two people on the teeter-totter, one on each end, and they start to play. As one of them pushes up, the other goes down, and as the lower one then pushes up in turn, the person who was up comes down. Aperture and shutter speed work the same way. You use both aperture and shutter speed to set the camera to let in the perfect amount of light; when you have found a combination of the two that works, realize that it is not the only combination that will work. I could open the aperture by one f-stop letting in twice as much light, and then choose the next highest shutter speed which will let in half as much light. Those two actions will cancel each other out and you will still have the right amount of light, but with a different combination for aperture and shutter speed. You could repeat that process again, giving you another combination of aperture and shutter speed that will work. Aperture and shutter speed work hand-in-hand. So which combination is the best? We’ll talk about that in the next blog.

ISO

What about the ISO setting, formally known as the ISA. The normal values for ISO are 100, 200, and 400. The bigger the ISO the more light is allowed in, the lower the ISO the less light is allowed. Nowadays they can go as high as 6400. Think of the ISO as a magnifier. If you find the perfect combination of shutter speed and aperture and then the sun starts setting and the amount of light starts to decrease, by simply changing the ISO from 100 to 200 you will let in twice as much light without having to change the aperture or shutter speed. Typically this is not played with as much as aperture and shutter speed. Usually if you are outside on a sunny day you will set the ISO to 100, if it is a cloudy day or you are shooting indoors with or without a flash, day, you might set the ISO to 400, letting much more light in. In the 20th century, I love saying that, when we used film, the particles that absorbed the light were a different size depending on whether you were using 100 or 400 ISO. For 400 ISO to let in more light, the particles in the emulsion had to be bigger, causing the images to be grainier. Sometimes this was unattractive, and other times it was more artistic, depending on your taste.

Choices: Which do you adjust and why

OK, so if you can use all three of those settings to adjust the camera to let in the correct amount of light, which one would you change and why? Stay tuned to my next blog, Photography: The creative side of aperture and shutter speed.