Getting started in the world of digital photography today can seem overwhelming. Our digital SLRs have more buttons, dials, and menu options than any person can reasonably be expected to keep track of.
Don’t be fooled. If we brush aside the terminology and sales gimmicks, photography today is just as simple as it was 50 years ago; maybe even simpler.
There are really only three things that you need to learn to understand photography. Once you understand these three basic elements, and how they relate to each other, you’ll only be limited by your own creativity and desire to practice. These things are:
- Shutter Speed
- ISO / Film Speed
That’s it. Once you understand how these things affect your images and how they relate to each other, everything else just falls into place. Each of these three elements affects your image in two ways: one is physical, and one is creative.
From a mechanical perspective, shutter-speed is pretty simple. I think we all know that in order to make a photo, our camera’s sensor (or film) needs a certain amount of light, and the shutter is simply a door to let light into an otherwise light-proof box where the sensor resides. Shutter Speed is the duration that the shutter is open, and as you’d expect, the longer it stays open, the more light is able to get to the sensor. If the shutter stays open for 2 seconds, twice as much light gets through as if it were only open for 1 second, for example, and 1/2 of a second lets in twice as much light as 1/4.
From a creative perspective, the effect of shutter speed is also pretty easy to understand. Since the sensor is exposed to light for as long as the shutter is open, it records an image of how far the subject moves during that time. A human can move quite a bit during one second, or even a half-second, so a 1 or 1/2 second shutter speed will record a blurry image of a moving person. On the other hand, even the fastest person can’t move very far in 1/1000th of a second, so that shutter speed will be great for stopping action.
Not as many people are familiar with what a camera’s aperture is, but there’s nothing difficult about it, either, once you see what it is. If you look into an SLR lens, you’ll see a set of blades that form a hole in the middle to let light pass through. That hole is the aperture, and the lens can move those blades to make the hole smaller or larger. The larger the hole, the more light gets through, obviously. Your camera’s aperture control, then, is another way to change how much light gets to the sensor.
Changes in the aperture also change how your photos look. The size of the aperture controls how much of the image appears to be in focus behind and in front of what you’re focused on. For example, suppose that you’re taking a picture of somebody who is standing across the room from you, and you can see trees through the big window behind them. If you take the picture with the lens’ smallest aperture (which lets in the LEAST amount of light), the trees in the background will also be relatively sharp in focus. However, if you take the photo using the lens’s largest aperture, the trees in the background will be very blurry, maybe not even recognizable as trees.
This effect is called “Depth of Field”. When the background gets blurry very quickly as it gets further from the subject, we call it “shallow” depth of field. If most of the picture appears to be in focus, from near to far, we call it “deep” instead. Although I’ve been talking about the background of the subject, the same thing is true of the foreground; in fact, foreground objects go out of focus even more quickly than background when depth of field is shallow. The term “Depth of Field” is frequently shortened to “DoF” on this website and on the internet in general. So to summarize, we can say that the use of small apertures creates greater (deeper) DoF, while using larger apertures creates shallow DoF.
Those of you who used to buy film will recall that you had a choice of different types. In most stores, you could buy 100, 200 and 400 speed films, and in a good camera shop, you could buy many more than that. These numbers are the film’s ISO rating, sometimes called the film-speed (or before the 1990s, it was called the ASA). With film, the higher the number (eg, 400, 800, 1600), the more “sensitive”1 the film was to light, so it could be used in darker environments. The lower the number (eg, 50, 100, 200), the less sensitive to light it was, making it better suited to use in bright daylight.
So why wouldn’t people just shoot ISO 1600 film all the time? Unfortunately, higher speed film was also more grainy and had duller colors.
Strangely enough, ISO is almost exactly the same in digital cameras. Most cameras have a base ISO setting of about 100. To increase the apparent sensitivity of the sensor, the camera amplifies the signal 2 that the sensor captures, and modern cameras can generally be pushed all the way up to ISO 6400, 12800, 25600 or higher. This gives them the ability to capture photos in pretty low light, but unfortunately, all of that extra amplification also increases the background data from the camera’s electronics. Think about an audio recording of a voice you’ve made where the voice was too quiet… maybe you recorded a video of someone across the room with your phone, or you recorded a lecture from the back row and it’s hard to make out the voice. You can turn up the volume when you play it to make the voice louder, but that also increases the background hissand other noises from the room, so it’s often still hard to hear.
The same thing is true with a high ISO setting. Shooting at high ISO “turns up the volume” of a small amount of data captured from the sensor, but it also turns up the background noise from the camera’s electronics. The result is a very grainy looking image, usually with dull or inaccurate colors and lower detail resolution. This phenomenon is known as “digital noise”.
A Game of Trade-Offs
As you can now understand, photography is a game of trade-offs between these three factors. Suppose you take a photo at a medium aperture, medium shutter speed, and medium ISO and its exposure is correct (fills the bucket), but the motion is a little blurry. We know that to stop action, you need to use a faster shutter speed (don’t leave the water on for so long). But if you ONLY change the shutter speed, then your “bucket” isn’t going to fill up. To make up for the change in shutter speed, you either need to let in more light with a larger aperture (bigger hose) or use a higher ISO (smaller bucket). But if you use a larger aperture, you get a shallower depth-of-field, and therefore, a more blurry background. If you use a higher ISO instead, you get more digital noise. In some cases a blurry background is desirable, so this may be an easy choice.