How Cameras Work

Kinds of Photography

Great Photographers

Digital Camera Advantages

Features to Look For

More Features to Look For

Professional Cameras

Accessories and Summary

Camera Care

Useful URLs

Annotated Bibliography


Digital Camera Features to Look For


When you go looking for a digital camera here are some of the things to consider.


Many of today's point and shoot digital cameras have no viewfinder. A viewfinder consists of a small eyepiece at the top of the camera that looks out through a window on the camera's front and shows the field of view that will be encompassed by the picture. Nowadays a few "mirrorless" cameras come with excellent electronic viewfinders (EVF's). Instead of simply being a way to frame your picture the EVF can tell you whether or not the picture's in focus and can tell you important things like your shutter speed, aperture, and sensor sensitivity (ISO). If your camera has no EVF or viewfinder you'll have to compose the picture with the liquid crystal diode (LCD) display on the camera's back -- the same LCD you use to view menus and stored pictures. Whether or not this is a problem depends on what you plan to do with the camera. If most of your pictures will be static scenes: landscapes, buildings, family groups saying "cheese," etc., then composing on the LCD may be satisfactory. But if you plan to do street photography, wildlife, or any kind of photography that involves moving subjects, then for three reasons you'll want a viewfinder: First, since every time you move the camera, even slightly, the camera has to re-draw the scene on the LCD, composing on the LCD can be difficult. Second, holding the camera at arm's length in order to see the LCD is a lot less stable than holding the camera to your eye with both arms pressed against your sides. Chances are that unless you can brace yourself against something your pictures will have at least some blurring from camera shake. Finally, if the light's bright you may not be able to see the LCD display well enough to frame your picture.

Auto Focus

There are three kinds of auto focus in use by modern cameras: infrared ranging, contrast detection, and phase detection. Most inexpensive cameras use contrast detection, which moves the focus back and forth in a series of successive approximations until the contrast along edges, closely spaced dark and light areas, is maximized. Some cameras use a combination of infrared ranging, which bounces an infrared beam off the target to get coarse focus, and contrast detection, which does the final zeroing-in. Most single-lens reflex (SLR) digital cameras use phase detection, which splits the incoming light into two images and measures the distance between the images. Contrast detection focusing is slow, phase detection focusing is extremely fast.

Manual Focus

Most digital cameras have a way to switch to manual focus. If auto focus is fast and accurate, why would you need manual focus? Well, if you're trying to shoot a picture of something behind a chain link fence, for instance, auto focus is likely to focus on the fence, not the subject. If you need manual focus for a lot of the pictures you shoot you should consider a single lens reflex or a mirrorless camera with a good EVF, which lets you look out through the lens to focus the picture. The other alternative is to focus on the liquid crystal diode (LCD) screen on the back of the camera, which is difficult and, as stated above, sometimes leads to blurring.

Light Metering

Digital cameras use three different methods to meter the brightness of the scene you're about to shoot. The most common method is matrix metering, which goes under various names depending on the camera manufacturer. Matrix metering takes readings from a grid of points on the sensor array and more or less averages the brightnesses. If you're shooting an evenly lighted scene this method should give you a reasonably accurate exposure.

A second method is spot metering. Cameras that let you use spot metering usually have a small circle or square in the center of the viewfinder that shows the "spot" the camera is going to meter. If you're shooting someone's face and the light's coming from behind the face, you need spot metering. If you use matrix metering the bright background probably will cause the camera to underexpose the subject and the face will be too dark.

The third method is a center weighted average. With this method the camera takes into account all or most of the points on the sensor array but emphasizes the brightness of the area toward the center.

If you think you might work in difficult lighting conditions you should consider a camera that will let you switch between these three methods.

Another thing to look for is the ability to meter on a spot or an area and then lock that exposure while you move the camera to frame and focus on what you want to shoot. Most digital cameras lock the exposure when you depress the shutter button half way. Most professional cameras also have a separate button that will let you lock the exposure independently of the shutter button.

Exposure Compensation

This feature is related to metering. If you're about to shoot a scene that has a lot of dark areas interspersed with bright areas, and you can see that none of the three metering methods on your camera is going to give you an accurate exposure compromise, you need to be able to tell the camera to expose the picture at a level below or above the level it would use from the results of its metering. Exposure compensation is the only real control you have over exposure if you're doing point-and-shoot, and it can save pictures you'd otherwise lose, but using it effectively depends very much on your experience with the camera.


Not long ago cameras came with fixed focal length lenses (called "prime" lenses in the industry). If you were working with a 35mm camera you'd carry a gadget bag with a 35mm wide angle lens, a 50mm normal lens, an 85mm "portrait" lens, and a 135mm long or telephoto lens. Sometimes you'd carry a 28mm, very wide angle lens and maybe a 200mm or more very long lens. Even back in the fifties zoom lenses were available but they had such extreme distortion at their minimum and maximum ranges that they weren't much use for serious work.

Nowadays most cameras come with zoom lenses and most of the distortion problems have been solved, though there's still a little bit of "barrel" distortion at their shortest (wide angle) setting and some "pincushion" distortion at their longest (telephoto) setting. Barrel distortion distorts straight lines outward so that a box looks like a barrel. Pincushion distortion distorts straight lines so they pucker in, like the edges of a pincushion.

Some "consumer" cameras offer two kinds of zoom: optical and digital. The only thing that matters is optical zoom. Digital zoom is nothing but a marketing ploy. All digital zoom does is crop the picture so that you record less pixels of information than you'd otherwise record. Your computer can do a better job of "digital" zoom than your camera can.

Aperture Range

The lens's "aperture" is the size of the hole that's going to let in the light. The size of the hole is determined by a diaphragm inside the lens barrel that closes and opens. Effective aperture is measured in f stops. "f" is the ratio between the focal length of the lens and the diameter of the hole. If you have a 50 mm lens that can open all the way up to a diameter of 50mm, you have an f/1.0 lens. Standard f stops run 1.0, 1.4, 2, 2.8, 4, 5.6, 8, 11, 16, 22 and 32. As you go down the f stop range, each of the stops (smaller hole, higher number) lets in half as much light as the stop above it. I know, it doesn't look linear, but Pi is involved and it is linear as far as the effective amount of exposure is concerned. (The word "stop" also is extended to shutter speed. To increase exposure by one stop with the shutter you'd cut shutter speed in half.)

Some cameras are advertised as having "fast" lenses. Exactly what "fast" means is determined by the company doing the advertising, but on a relative scale "faster" means that the lens has a lower minimum f stop and lets in more light when the lens is wide open than another "slower" lens. The advantage of this is that you can take your picture with less light. But don't get carried away by the advertising claims. In most cases a one-stop difference in the wide-open aperture won't make all that much difference in the result.

What matters most about the lens's aperture range is the control it gives you over depth of field. "Depth of field" is the length of the area out in front of you over which the picture is going to be in sharp focus. Depth of field doesn't start suddenly at, say six feet, and end abruptly at twenty. Loss of focus is gradual. The area encompassed by depth of field is the area within which focus is acceptably sharp. What "acceptably" means is for you to determine. But if you want to shoot a portrait of someone against a distracting background, and you want the background to be soft and out of focus, you'll want to shoot with a moderately long focal length lens opened up to its maximum aperture so that, in the best case, depth of field will start at the person's nose and end at the back of her neck or even just beyond her ear.

The other extreme is when you want to have everything out there in focus from, say ten feet to infinity. To do that you may need to use an f stop of 8 or 11 or even 16. Edward Weston and Ansel Adams used to work with apertures of f /64 on their view cameras to get the sharpness they got in some of their pictures.

I won't try to cover this fairly complicated topic in detail here. The point is that when you buy a camera you want its lens to have a range of apertures that will give you the control you need. If you don't think you're going to need that kind of control, don't worry about it.

Aperture Priority and Shutter Speed Priority

You can't control depth of field unless you can leave automatic (usually called "program") mode and set the aperture independently. Most good digital cameras will let you do that. If you use aperture priority to set the aperture independently the camera should compensate by setting shutter speed automatically to give you correct exposure. If you're shooting sports pictures you might want to be able to control the shutter speed independently and set it to 1/600 second or faster. If you set a shutter speed in shutter priority the camera should automatically set the aperture to give you the correct exposure -- if there's enough light to let it do that.

Most good digital cameras will also let you go into full manual mode so that you can set both aperture and shutter speed manually. Why would you want to do that? Well, you can be faced with a situation where none of the camera's reflected light metering modes quite does the job. When a scene contains both wild variations in brightness and a lot of movement, rather than try to pick out a metering point you may be better off using an incident light meter -- a meter that tells you how much light is falling on the subject instead of how much light is reflected from the subject -- and locking the camera to a fixed ISO, aperture, and shutter speed just as if you were shooting with an old-time film camera.

Maximum ISO

"ISO" stands for "International Organization for Standardization." With respect to film, the proper moniker is "ISO film speed," but it gets shortened to ISO. Before internationalization became politically correct, film speed was measured in ASA ratings, which stood for "American Standards Association." ASA film speed ratings were developed by Kodak in the 1940's, adopted by the ASA, and used worldwide. Now the measure has been co-opted by the ISO and has become "international."

If you go to the drugstore to buy film (at the time I wrote this you still could do that) you'll find ISO ratings on the film boxes of 200, 400, 800, or even more. Film with an ISO rating of 800 is very fast. ISO 200 film is pretty slow. "Slow" means you need more light for proper exposure. "Fast" means the opposite.

Unfortunately film speed doesn't come for free. There's a tradeoff. To get faster film you need larger grains of silver in the emulsion and you get larger visible grains in the print. If you enlarge a 35mm negative made with ISO 800 film to a 16 by 20 or 20 by 24 inch print the grain becomes very visible. A digital camera shows a similar effect as the effective ISO increases. Of course the pixels on the CCD array don't get larger as you increase the speed, but as the signals from the pixels gets amplified you get more "noise." Noise is random electrical static that shows up in a print the same way grain shows up in a print from film. Digital noise produces little dots (we call them "artifacts") that may be scattered over the whole scene, or over parts of it.

Since comparing a digital camera's speed with film ISO ratings is something like comparing an apple with an orange (not quite as far off as comparing it with a banana) the result is an approximation. Equivalent ISO speeds for a consumer digital camera will range from about ISO 50 to ISO 800. If you buy a digital single lens reflex (DSLR), ISO speeds may go much higher. How fast you need the camera to be depends on what you want to do with it. If you're going to shoot action shots on a dimly lighted basketball court you'll need a fast camera. If you're going to shoot mountain scenes with the camera on a tripod, speed isn't an issue.

Most consumer digital cameras adjust their speed automatically to the shooting conditions when they're in point-and-shoot mode. But I found that my point-and-shoot digital cameras didn't necessarily go up to their highest speed ranges automatically. If I decided I needed lots of depth of field and the light was fairly dim I'd need to manually adjust the aperture to, say f 8. If you do that you'll probably also need to manually adjust the ISO speed to the camera's maximum. Be sure you can adjust your camera's speed manually.


The most important thing about on-camera flash in a "consumer" point-and-shoot is to have a way to turn it off – permanently if possible. Nothing destroys the beauty of a scene's ambient light more quickly than on-camera flash. Probably three quarters of the family pictures I see have people with red eyes, featureless faces, and dark shadows behind them. These are all caused by on-camera flash. Sometimes when I go to a play or a concert the performance will be marred by people shooting flashes – even from the back of the balcony, too far away for the flash to do anything useful but close enough to annoy the performers and the spectators. I like to take pictures of people in museums, but most museums nowadays won't let you in with a camera. That's because the same boors who were shooting at the performance have been in the museum flashing their flashes.

Ironically, the fact that almost all consumer cameras come with on-camera flash and that many cheap cameras come with a flash the user can't turn off is a boon to street photographers. Most people think that if there isn't a flash, you didn't take a picture. That means you can bang away with your camera in a crowd and not get mobbed.

Unless you're a spy copying classified documents, the only time on-camera flash on a point-and-shoot is useful is if you need "fill light." The classic example is where you're shooting against the light and you want the background exposure to be more or less consistent with the foreground. But even then you're better off if you can use a white umbrella to reflect diffused light back onto the foreground.

On the other hand, in many situations faced by professionals and serious amateurs, flash is essential. With professional equipment you can place flashes at various positions off the camera and control them with the on-camera flash. This is a complicated subject I'll leave for another lecture.

Self-Timer and Remote Trigger

If you're going to take a picture of the whole family with you in the picture you'll need a self-timer or a remote trigger. To use the self-timer you turn it on, click the shutter button, and then step into the picture. Ten or so seconds later the camera will trigger the shutter and take the picture. With the remote trigger you set up the camera, focus it, step into the group, hide the trigger in your hand, tell everyone to say "cheese," and then press the button on the trigger.

If you do long exposures from a tripod, longer than the camera can manage on its own, you may need a "cable release" that'll let you open the shutter and hold it open for as many seconds as the exposure takes. Cable releases used to be coaxial cables with an inner core that moved when you pressed the button. Nowadays most of them are electronic.