Digital SLRs versus Point-and-Shoots

What's the difference between them?

POINT-and-SHOOT CAMERAS
  • have a separate viewfinder lens (or none)
  • use streaming video sensors
  • usually offer video clip recording
  • have a built-in objective lens
These cameras are designed to focus on the most common types of photography which untrained users are likely to want: snapshots of family and friends in well-lit buildings or outside. The focus on convenience allows the camera to make more choices automatically, saving the user time at the expense of flexibility.

DIGITAL SINGLE-LENS-REFLEX CAMERAS
  • uses the objective lens for viewfinding
  • uses a mirror to achieve that ability
  • has no video capabilities
  • has an emphasis on low-noise photosensors
  • usually allows switching objective lenses
These cameras are designed for their flexibility. They offer a dazzling array of controls and options, allowing excellent results in a very wide range of situations. The camera leaves more choices in the hands of the photographer. This flexibility comes with a price; even simple images are often in need of individual post-processing on the computer.

Why does my Point-and-Shoot take forever to focus and shoot?

A point-and-shoot digicam has a couple of handicaps when it comes to focusing quickly just before taking a photograph.

First, many of these automatic cameras use the image sensor itself to determine focus. This depends on the streaming video design of these sensor chips. Essentially, each time the sensor collects an image, a piece of software looks for any "contrasty" edges in certain areas of the image, such as around the center. If these are found, the camera computes just how sharp the contrast is, numerically. This information is then fed to the focusing engine to try to improve those edge scores. It can take two or three streaming frames of video to decide if the lens is moving in the right direction, and by the right amount.

Alternatively, some cameras employ a second "focus assist" beam of light (white or infrared) and a dedicated focus sensor to determine the distance to the subject. While this system is a bit faster, because it only needs to be sampled once, it also has some weaknesses: a thumb on the wrong part of the camera body can block the sensor or beam, or bright sunny conditions can make it hard for the camera to see its own focusing light.

The second major handicap is that the motors inside a point-and-shoot digicam are usually made very inexpensively, and to operate under the lowest possible electrical power. This usually means nylon gears and simple stepper motors, rather than metal gears and ultrasonic motors.

The third major handicap for automatic cameras is the "live preview" feed from the streaming video sensor itself. These sensors usually need to switch into a separate capture mode, and to drain any charge buildup from the silicon before it can capture an image. In cameras which have a mechanical shutter as well as the electronic shutter, it must now be closed for this period, and then re-opened to start the exposure.

Each of these weaknesses only takes a fraction of a second, but when your child is standing precariously on one foot, any delay can seem like an eternity, and every wasted moment adds up.

Why can't I get a live preview on the DSLR screen?

The point-and-shoot cameras use streaming video sensors to allow a "live" preview of the scene on the camera's rear screen. It's a very handy system: see the digital picture, snap the digital picture. It's so handy that some people can't imagine a digital camera without that feature.

However, for two key architectural reasons, digital SLRs can't provide a live preview. Some people have been known to return their "defective" camera upon that discovery.

Firstly, the term SLR stands for Single Lens Reflex. The meaning of Single Lens seems simple enough: it doesn't have a pinhole viewfinder in the corner so it uses its own objective lens. But Reflex refers to a mirror. An SLR uses a mirror to allow the viewfinder to see out the lens until it's picture-time. The mirror flips up to let light go to the image sensor. With the mirror usually in the way, the sensor can't see much of anything.

Secondly, streaming video sensors waste a lot of space on their precious silicon on the various circuitry designed to provide electronic shuttering, video output, and so on. DSLR sensors spend as much of that space on one thing as possible: collecting light. This makes for less random noise grain in the images, which is of great importance to professional photographers.

It's not all bad, using an optical viewfinder. Looking through the lens gives immediate and accurate feedback about the lighting and composition, even for fast-moving objects. There's no lag-time between the action and your eyes, like a video stream would have. Also, holding your camera against your face will help to avoid shaking the camera, a big source of unwanted blur. The extra mass of most SLR cameras and lenses can also serve to stabilize the shot.

Why do my DSLR images seem so soft and dull?

The first comment that many new DSLR owners have, after realizing that they can't use a preview screen to compose their shots, is that the images which they download to their computer just don't seem very sharp and vibrant.

Another way of saying the same thing is in the form of a question: "How can I get images which need no post-processing?"

To answer this, we go back to the reason that point-and-shoot cameras exist: to make the camera as fully automatic as possible. These cameras are designed to take excellent pictures, but only of the most common snapshot subjects. If the shooting conditions don't fall under the bright-lights-and-casually-composed category, then an automatic camera will probably give poor results.

These automatic digicams make a lot of assumptions, and use those assumptions to make choices for the photographer. They assume that everyone loves super-sharp focus images. They assume that anyone would prefer a vibrant and colorful image. They assume that the stronger the contrast, the better. Every image goes through an aggressive sharpen-contrast-saturate program inside the camera.

On the other hand, while this gives you great snapshots, it won't give you great wedding shots, or floral shots, or wildlife shots, or astronomical shots.

Digital SLR cameras make only one assumption: that you want the best possible digital data you can get. The in-camera processing features are far more conservative, erring on the side of under-processing, so that you can make your own choices later. While this means your snapshots won't look as vibrant and oversharp right out of the camera, you can still get those results with a little work. The same goes for many types of photographs which the lesser digicam just can't handle at all.

Photograph of photographers by Edward Lappin. Ed, contact me; I couldn't find your email address.


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