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Photography Kick-start Guide: How Your Camera Works

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Twice a month we revisit some of our reader favorite posts from throughout the history of Phototuts+. This tutorial was first published in August, 2009.

Most photography tutorials, including most of the ones you’ll find here on the Tuts+ network of web sites, assume a certain base level of knowledge. But what if you've only just decided you want to make the leap into taking photos with manual settings?

In this tutorial you'll start to begin to learn the fundamentals of photography - fundamentals that will allow you to start reading and using more advanced tutorials, and manipulating the manual settings on your camera. Here we cover exposure, how the camera works, the shutter, focus, light, depth of field and ISO.

As in any specialized field, photography has a lot of jargon. This tutorial will introduce specialized camera terminology where appropriate, but I made a conscious effort to avoid using it through most of the tutorial if a more accessible word would convey the same meaning. What we want for you to learn here are the photographic concepts and having to juggle newly introduced words that aren’t yet familiar to you gets in the way of that.

Lastly, these concepts apply to photography in the broadest sense. No matter what kind of camera you use, the most basic fundamentals of photography will apply equally.

1. Making the Exposure

What is “exposure”? This word may be one of the more confusing ones you’ll come across. It’s used in many different contexts and has a slightly different meaning in each. Sticking with the broadest sense, exposure, in a nutshell, is the picture you are taking (or the one you took.)

When you press the button on your camera, you are literally “exposing” it to light. All photography is captured light. Without light, there is no picture. Again, boiling it down to its most fundamental level, we don’t see things we see the light reflected off things.

The light reflected into your eyes is how you see -- and how your camera sees.

Think about this for a moment. Let’s take something simple like a rock. If you hold it in your hand, go outside and look at it in bright daylight and you see a rock. Take it indoors under artificial light and you still see a rock. Take it into a blackened room in which there is no light at all. You can feel the rock, so you know it’s still there, but you can’t see it because there is no light. All along, what you were seeing wasn’t the rock itself but the light reflected off the rock.

When we take a picture, what we’re really doing is recording the light reflected off whatever it is our camera is pointed at. That is the exposure.

2. Recording What the Camera Sees

The next step on our journey of understanding how cameras work is learning how, exactly, a camera records what it is exposed to. Most popular today are certainly digital cameras. These have a highly specialized computer chip inside them that is extremely sensitive to light. In the interest of keeping this tutorial easy to follow, I’m going to call it “the film”.

The computer chip is the 'film' that your digital camera uses to take pictures. Film is familiar to most people because, before digital, film is what we used to record our exposures. In this case, the film was literally a thin 'film' of plastic that had been coated with light-sensitive chemicals. Before film, photographers used glass plates which they often had to coat with chemicals themselves. Kodak, Fuji and Agfa weren’t in business yet!

A camera, at its most basic, is nothing more than a light-proof box. It has an opening that is covered up by a light-proof curtain called the shutter. Directly in front of the shutter is where we put the lens. We’ll discuss both the shutter and the lens in more detail further on.

When you press the button on your camera to take a picture, what happens is that the shutter opens and exposes “the film” to light. For just a very brief moment. Less than the blink of an eye. The film is so sensitive to light that that very brief exposure is all that it needs in order to see and record whatever was in front of the camera when the shutter was opened.

Back in the old days of film, you then had to advance the film. This was usually accomplished either by a lever on top of the camera, a wheel on back or a motorized drive mechanism built into the camera. It was sliding the film along a track to expose a fresh portion.

If you’ve never pulled the film all the way out of a film canister, just know that it’s about 1/2” (24cm) high by around 3’ (1m) long. Each time you press the button and open the shutter, only a very tiny segment of the film (about 3/4” or 36cm) is actually exposed to light. The rest has been carefully shielded. In the really really old days of glass plates, the photographer had to actually remove the plate from the camera and store it in a light-proof container until he/she could develop it. If you wanted another picture, you had to insert a new glass plate.

In the digital age, the chip inside your camera saves the image it recorded to the camera’s internal memory buffer. After the chip saves its information to the camera’s internal memory buffer, it clears itself and gets ready to take another picture. The camera’s internal memory buffer can usually hold all the information for five to ten pictures. In the meantime, yet another process takes all the information from the camera’s internal memory buffer and writes it to the card. (Most digital cameras use some type of removable memory card. CF and SD cards are most popular today but there have been around a dozen different types over the years.)

This writing of data to the card is a comparatively slower process. That’s why your camera uses an internal memory buffer, so it can be ready for the next picture more quickly rather than making you wait for it to write everything out to the card.

3. How the Shutter Works

While understanding exactly how shutters work is not necessary for taking good pictures, an explanation follows because it may help with understanding other fundamental concepts in photography.

The shutter.

First, let's define a couple of terms.

Frame: This is another word that has a couple of different meanings. For instance, one exposure (one picture) may also be called one frame.
For the purposes of our discussion about how shutters work, the frame is the opening in the camera body that the shutter covers. When the shutter is open, light passes through the frame to expose the image.

Curtain: What we tend to generically call "the shutter" is actually a collection of parts. Most importantly, there are really two different light-proof curtains that make up the whole shutter assembly. For our purposes here, we need to be able to refer to each of the shutter curtains individually.

The first one ("Curtain A") is attached to the top of the frame. It expands downward to cover the frame and contracts upward to expose it. The second ("Curtain B") is attached to the bottom of the frame. It expands upward to cover the frame and contracts downward to expose it.

Let's assume that currently Curtain A is expanded downward, covering the frame. Curtain B is then contracted, letting Curtain A do the work of blocking light from getting through.

When you press the button on your camera to take a picture, the following sequence of events takes place:

  • Curtain A contracts upward, exposing the frame.
  • Curtain B expands upward, covering the frame and ending the exposure.

The interval between these two events is the shutter speed. The next time you press the shutter button, Curtain B contracts downward followed by Curtain A expanding downward. They will keep alternating in this way for the life of the camera. On old film cameras without motor drives the curtains did not alternate. Rather the winder ‘cocked’ the shutter, resetting it for the next exposure but all other principles explained here still hold true.

At slow shutter speeds (i.e.- 1/15th second), the movements of the two curtains may be separate events. During almost the full duration of the exposure, the frame is left completely uncovered. At fast shutter speeds (i.e.- 1/2,000th second), both curtains may be moving simultaneously with only a slit between them moving up (or down) across the frame.

Suppose there was only one curtain. (Let's use Curtain A.) The curtain would contract upward then, after the duration set by your shutter speed, expand downward to end the exposure.

The top section of the frame would be the last exposed to light and the first shielded. For a relatively long exposure (i.e.- 1/4th second), the difference in exposure time between the top and bottom of the frame as a percentage of the total exposure time, would be insignificant and you'd hardly notice a difference. At faster shutter speeds (i.e.- 1/1,000th second), the difference as a percentage of total exposure time would be much more significant. You'd end up with an image that gradually darkened from bottom to top.

Having two curtains also allows for much faster shutter speeds. Think of the mechanics involved in an object moving very rapidly in one direction, stopping, then reversing course and moving very rapidly in the opposite direction, all while allowing you to maintain precise control over its speed of movement. Even if it could be done, the mechanical strain would result in faster wearing and greater breakage of parts.

4. Bringing It Into Focus

At its absolute most basic, we’ve already covered everything that’s technically needed for photography: a light sensitive medium (the film or digital camera chip), a light-proof box (the camera body), an opening to allow light to get to the film (the frame) and a way to control the light getting to the film (the shutter). If you were to make a pinhole camera, these are all the parts you’d need. Everything else simply makes photography “better”; faster, more convenient, and more flexible.

The next part we’ll add to this very basic setup is the lens. Your camera may have a built-in lens permanently attached or it may allow you to change lenses.

What the lens does is take all the light in front of the camera and focus it.

A projector has a flat point of focus.

Think of an old fashioned slide projector or an old film projector. If you took one of those slides or a section of that filmstrip and held it up between a lamp and the wall, the light from the lamp would not project any kind of meaningful image onto the wall. At best you would see vague patches of colorful light. With the projector, you use a lens to focus and concentrate that light onto a more defined area rather than just letting it spread in all directions.

The lens on the front of your camera does exactly the same thing, only in the opposite direction. Instead of focusing the light that would otherwise spread randomly outward, it takes the light that already is spread randomly around and focuses it onto “the film”. (By the way, your eye is a lens too. It has exactly the same kind of structure and the same basic features as any camera lens.)

Let’s look at how a lens is made and then we’ll talk about the mechanics of focusing. (We’re going to skip over aperture for now and deal with that in its own section.)

Lenses focus light on to the film.

Even the very simplest of lenses consists of at least two “elements”. An element is a single piece of glass. (I say glass but it could also be made from plastic or even from other exotic materials.) Every element has at least one curved surface. Look closely at a pair of eyeglasses. You’ll notice that they’re not just flat plates of window glass. Usually the front surface of each lens is curved outward, away from the wearer, and the rear surface is curved inward, toward the center of the lens and also away from the wearer.

On a camera lens, elements may have one flat surface and one curved surface, they may have two surfaces curved in the same direction (just like eyeglasses) or they may have two surfaces curved in opposite directions, either both outward or both inward.

If there were just a single piece of glass, it would modify the light but there would still be no way to focus it. Going back to our example of holding a slide or section of filmstrip between a lamp and the wall, if you insert a magnifying glass or eyeglass lens into the equation, you will notice a change to the light reflected on the wall but you still couldn’t make the reflection into a sharp image.

Adding a second piece of glass, also curved on at least one surface, gives you the ability to focus. Focusing is accomplished by moving
the two pieces of glass closer together or farther apart. (They can also be moved, as a set, closer to or farther from the film.)

When light passes through each of these glass elements, the curved surface(s) “bend” the rays of light. Most lenses have many more than two glass elements and, together, they may bend the light multiple times in complicated ways. Sometimes two or more elements may be glued together. These are called groups. (Just to keep things confusing, a single element all by itself is also called a group.) So if you look at technical specifications for a lens you may see something like “13 elements in 7 groups”. Now you have an idea what that means.

In the end, the goal of all this is to bend and concentrate the light rays so that they form a sharp, clear image on the film.

lens schematiclens schematiclens schematic
Lens elements.

5. Fine-tuning the Light

With a lens on the front of the camera, you can choose between having an image that’s in focus or one that’s out of focus but there really is no in between. In order to fine-tune the effects you can get and increase your creative possibilities, we need to add more.


The aperture is a set of light-proof blades arranged in a circle inside the lens. At the center of the circle is an opening much like the hole in the center of a doughnut. (True to form, the word “aperture” refers to two different things. The entire assembly itself is called the aperture, or sometimes the diaphragm, but the hole is also called the aperture. When most people say aperture they are referring to the hole and not the assembly of parts which form the hole.) The size of the aperture’s opening can be adjusted in very precise increments to control how much light is allowed to pass through the lens and get to the film.

Even if your camera doesn’t provide you a way to control it directly, all but the simplest cameras employ apertures.

The size of the aperture opening is never measured in direct units. For example, you’d never hear someone say “my aperture is 10mm”. Instead, it’s expressed in relation to the focal length, or zoom length, of the lens. It also follows a logarithmic scale, making the whole concept even harder for non-rocket scientists to follow. So, for example, if your aperture opening were 10mm in diameter and you were using a 100mm lens, you would actually say your aperture was f10. This means that the diameter of the aperture opening was 1/10th that of your focal length. That same 10mm opening on a 50mm lens would be f5 because the diameter is only 1/5th that of the focal length. (The “f” in that expression is short-hand for “focal length”.) Confusing? Definitely. But there’s a reason for it. We’re getting there!

Typical aperture settings are: f1.4, f2, f2.8, f4, f5.6, f8, f11, f16, f22. Each of these is a whole stop -- exposure increments in photography are referred to as “stops” -- and each represents half as much light getting through the lens as the stop before it and twice as much as the stop after. Some lenses may open wider than f1.4 or close down smaller than f22, but they are not common.

Also, your lens may not even have the full range listed above. On the front of the lens you should find a marking such as “17mm f5.6” or possibly “17mm 1:5.6”. The f5.6 in our example represents the widest aperture that is available on that lens. So, in this example, you could use any of the settings from f5.6 to f22. The actual numbers on your lens may vary and if you’re using a zoom lens you’ll have two sets of numbers. The first refers to the shortest end of the zoom range and the second refers to the longest end of the range.

So just why are apertures measured the way they are? To understand that, you have to know what an aperture actually does.

  • The primary function of the aperture is to regulate the amount of light that’s allowed to pass through the lens and get to the film. Because the blades making up the aperture mechanism are light-proof, light coming through the lens can only get through the hole created by the mechanism. One of the things that all that bending of the light rays does is to squeeze the light through the hole. That way, when you close down the aperture, you do not see a bright center spot and darker edges.
  • A side effect, and the most important thing as far as photographers are concerned, is that changing the size of the aperture changes how much of your scene is in focus.

This is going to take a bit of explaining, so let’s give it its own section.

6. Depth of Field

Going back to our example of a slide projector or a film projector, the slide (or film) is flat and the screen onto which the image is being projected is flat. Projector lenses don’t have apertures because the amount of light they put out is a known and constant quantity and the two flat surfaces means they can focus from Point A (the slide/film surface) to Point B (the screen).

depth of fielddepth of fielddepth of field
Depth of field.

The real world is three dimensional. Your lens may be focusing all the light it sees onto a flat surface, but that light is all coming from non-flat surfaces. Technically speaking, a lens can only achieve perfect focus on a single plane at a time. As things get farther away from that plane, whether closer to or farther from the camera, they get progressively more out of focus. Up to a certain point, the degree of blurriness caused by being out of focus is so miniscule that it can’t even be detected by the naked eye. What you end up with is a range in which everything appears to be in focus even though technically only one point is actually in perfect focus. This range is known as “depth of field”.

In the interest of trying to cover all the jargon you are likely to come across in your photographic studies, there is another term called “circle of confusion”. Think of a pencil point. When the pencil is freshly sharpened it has a very fine point. Let’s say that any given point that is in the plane of perfect focus could be represented by the sharpness of this pencil point. As you use the pencil, it very gradually dulls. The point becomes rounder, larger and wider. The change is not sudden, so many of these intermediate degrees of sharpness might appear to be just as sharp as when the pencil point was perfect. We would say that those fall within the depth of field. At some point the pencil tip becomes larger and more dull. You can plainly see that it’s not as sharp as when the point was perfect. At that point, the circle of confusion has been breached and your brain no longer confuses the ever-so-slightly dull pencil point with the perfectly sharp one. You know that the pencil point is dull; or in this metaphor, you recognize that parts of your image are not in focus.

How all this pertains to aperture is that as you close down the aperture to ever-smaller openings, the depth of field becomes larger. That is, a much greater range within your scene appears to be in sharp focus. This can be useful, for example, if you are trying to photograph a large field of flowers that extends from only a few arm lengths away out to the horizon and want it all to be in focus.

This portrait-style picture leaves the background out of focus.

Understanding this phenomenon will help you to know that the opposite must also be true; as you open your aperture to ever-wider openings, the depth of field becomes smaller. This is often used in portraiture, where photographers often like to have the person they are photographing in focus but would like the background pleasingly blurred and out of focus.

I promised to explain why aperture values follow such a hard-to-understand logarithmic scale rather than just permitting direct measurement of the opening. Now that we’ve gone over a bit about aperture and how it works plus covered a few things about lenses and focusing, let’s briefly put it together. The reason is that the same diameter opening will make your pictures look different when you use lenses of different lengths. A diaphragm opening of 10mm would be extraordinarily wide on a 12mm lens, only modest on an 80mm lens and very small on a 300mm lens. The effect, both in terms of how much light could get through as well as depth of field, would not be the same from one lens to the next.

That would be like saying that a meter means one unit of measurement in Singapore, a completely different unit of measurement in Norway and another unit still in Australia. Without standardization, a unit of measure starts to become meaningless. So instead, the measure is expressed as a percentage of the focal length of the lens. This provides the needed amount of standardization so that the effect on your pictures (at least as far as aperture is concerned) is the same no matter what lens you are using.

The increments on the scale may seem somewhat random, but they are actually calculated in keeping with the halving and doubling that is common with all other photographic measures. In this case, halving or doubling the area of the opening and thus the quantity of light allowed to pass through.

7. Controlling Brightness Through Exposure Time

Photographers may get so caught-up in the secondary effect of aperture -- depth of field -- that they forget the primary purpose it was designed to serve; to regulate the amount of light allowed to pass through the lens.

We’ve already discussed that all of photography is the capturing and recording of light. It’s worth mentioning that all of the light a camera records is cumulative. Most often, your camera’s film or digital sensor only needs to be exposed to light for tiny fractions of a second in order to capture and record an image. When the light gets low, you may need to leave the shutter open longer in order to let more light in.

Ferris WheelFerris WheelFerris Wheel
Playing with exposure at night-time.

As long as the shutter is open, your camera is gathering light. If it happens that your image contains a moving subject and the subject’s speed of movement is faster than the shutter speed you’re using, it will register as a blur in your image. Knowing this can be very useful.

Sometimes, you may purposely want your subject to be blurred, or completely frozen. Knowing about the relationship between shutter speed and speed of subject movement will help you pick better settings. You don’t need 1/4,000th of a second to freeze someone moving at a walking pace when 1/125th of a second may do the job.

Conventional wisdom has it that faster moving subjects always demand faster shutter speeds. It can be useful to study the effect that different
shutter speeds have on an image. Do you want to freeze the action? Convey a hint of motion? Or let the motion produce an effect?

Controlling the shutter speed may be useful or necessary to freeze (or deliberately blur) a moving subject. For example, with moving water, a fast shutter speed will freeze individual droplets. A very long (slow) shutter speed will produce a flowing, cotton candy effect. There is a whole range of speeds available between these extremes.

8. Sensitivity to Light

So far we’ve talked about two different ways in which cameras manage the light that is used to make an exposure: aperture and shutter speed. There are two more ways in which cameras control light. One of the two ways is by adding more light. This is usually done through the use of flash. Flash is such a big subject, we’re going to reserve it for its own tutorial. For now, just know that it’s one of the tools available to you.

The other method is commonly called ISO. ISO is actually an acronym for the International Standards Organization. This is the group that helps to set standards for everything; from electrical output and tire sizes to the hardness of steel and the softness of cotton. They also set the standards for sensitivity to light.

From a photographic perspective, ISO is really a reference to “film speed”. Let’s step back and think of a film again for a moment. You can walk into any shop that still sells film and you’ll find a number of different varieties. You may see so-called “100 speed” film, “200 speed” film, “400 speed” film and so on. Alternatively, these may be marketed as ISO100, ISO200, ISO400 and so on. (Notice that we’re back on this halving and doubling of values that is standard throughout all photographic measurements.)

Consumer films typically range from ISO50-ISO800. Digital cameras typically range from ISO100-ISO400, though some can go as low as ISO50 and it’s becoming more common for them to go as high as ISO6400. At the extremes, specialty films can range from single digit ISO numbers to numbers of ISO30,000+.

The scale is the same for both film and digital. Here is a quick rundown of some ISO values you may see:

  • ISO25 is very insensitive, requiring very bright light.
  • ISO50 is twice as sensitive but still requires very bright light.
  • ISO100 is the mainstream default for both film and digital. It is used mainly in bright daylight or a comparable level of brightness.
  • ISO200 is the next whole increment in sensitivity. It is billed as an “all-around” film. Outdoors, this might be used around dusk and dawn.
  • ISO400 is the next whole stop. It can capture images in relatively low light, particularly indoors or during twilight hours.
  • ISO800 is for nighttime photos with limited light.
  • ISO1600 is for use in dark environments.
  • ISO3200 and beyond are for use in very dark environments.

As a rule, more sensitive media (higher ISO numbers) will yield images with more grain. In some cases, the graininess can become extreme, even affecting image quality. While often unwanted, this is sometimes used to enhance a certain “feel”.

There is also an inverse relationship between color saturation and ISO sensitivity. ISO100 will have little to no grain, will be very sharp and have vivid colors. ISO400 will generally have moderate but perhaps noticeable grain and muted colors. ISO1600 will usually have ‘extreme’ amounts of grain and very muted -- almost monochromatic -- colors.

9. Wrapping it all up

Here we've covered the basic parts of a camera and the ways that cameras can exercise a great deal of control over the light that makes up your photos. Together, these methods can be used in limitless combinations to achieve almost any effect you can think of. Each of these has side-effects that may or may not be desirable for the photo you want to take. Controlling how much light gets in by changing the aperture will increase or decrease your depth of field. Controlling how long the light is allowed in by adjusting the shutter speed will increase or decrease motion blur. Controlling how much light is needed by changing ISO may affect graininess and color saturation.

No one expects that simply reading through an article like this one time will suddenly make you an expert on this stuff. You may need to read over it a few times. You may want to come back to it from time to time to refresh your memory on a concept. The goal here has been to help you build a foundation whereby you can study our other tutorials and be able to follow along when some of these unfamiliar concepts come up.

Good luck and happy shooting!

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