What Is a DSLR Camera?

Digital single lens reflex (DSLR) cameras are popular, but why?

A DSLR, or digital single lens reflex, camera is camera that has the optics and mechanisms of an SLR, or single reflex lens, camera and the digital imaging capabilities of a digital camera. DSLR cameras are one of the most popular types of camera on the market because they capture professional-quality images, but are relatively easy to use.

DSLR camera in foreground with photographer in background

To understand how a DSLR camera works (and what makes them so popular) it's necessary to first understand how its predecessor, the SLR camera works.

How SLR Cameras Work

You may have seen an SLR camera and never realized it. These are the film cameras that were popular in the mid- to late-1990s. They consist of a camera body to which interchangeable lenses can be added. These lenses can vary, depending on the type of image a photographer wants to capture. Unlike today's digital cameras, photographers had to load a photographic roll of film into the body of the camera before taking pictures.

A Yashica Single Refex Lens camera sitting atop a photograph album.
 @tamus via Twenty20

Once the film was loaded, the camera worked using a reflex design. Light traveled through the camera lens to a mirror that reflected the image the camera was focused on to a pentaprism, which directed the exact image to a view finder.

Pre-owned SLR cameras can still be found, but manufacturers no longer produce SLR cameras. You can however, still buy photographic film for SLR cameras and there are still a few labs that will develop photographic film. If you want an idea of how an SLR camera works without trying to buy one, disposable (also called single-use) cameras work on the same basic principles as SLR cameras, but they almost always have only a 35 mm lens setting.

When the photographer was ready to take the picture, she pressed the shutter button, which flipped the mirror out of the way to allow the image to be projected onto the film. Settings that were manually adjusted by the photographer determined how long the shutter stayed open to capture the image.

Then, once an image was captured, the photographer had to manually advance the film using a lever on the top of the camera, to queue up the next unexposed cell on the film roll before taking another picture. The photographer may also need to adjust the settings on the camera or the focus of the lens before that next image was captured.

What made SLR cameras remarkable at the time was the mirror reflection capability. This allowed the photographer to see through the view finder (before the picture was taken), the exact image that would appear on the film.

How DSLR Cameras Work

A DSLR camera works the same way an SLR camera works with one important variation — instead of using light-sensitive film, DSLR cameras (sometimes referred to as Digital SLR) use digital imaging sensors, to capture the image that's displayed in the view finder or on the display screen. The photographer still sees the exact image that is captured, it's just the method of capture that is different.

Diagram of how a DSLR camera works.
Daveen Salinas

Removing the film from the camera also allowed some additional advancement in the mechanics of how a camera works. For example, instead of having to manually advance photographic film after each shutter press, a DSLR can capture a picture and then immediately capture another as quickly as the photographer can press the shutter button again. In some cases, this means that photographers can capture more, and better, pictures than was possible in the past.

Digital images that are captured by DSLR cameras are stored in a DCIM (Digital Camera Images) folder on an SD card. The image can then be retrieved from the storage card by a computer using a cable connection between the camera and the computer or by using an SD card reader. As SD cards (and their counterparts XD cards) increase in storage capabilities, photographers can take more and more photographs without having to worry about the cost of physical materials.

Don't confuse DSLR cameras with point-and-shoot cameras. Point-and-shoot cameras don't have interchangeable lenses (they're often referred to as fixed lens cameras), and most don't have the lens reflex capability that allows you to see the exact image you're capturing from the view finder.

Why Are DSLR Cameras So Popular?

Like SLR cameras, DSLR cameras have interchangeable lenses — you can have lenses for close-up pictures, one for wide angle pictures, and another for long-range pictures. That's part of what makes these cameras popular; they're versatile. But that's not the only reason photographers of all levels choose DSLR cameras.

Another reason is that DSLR cameras have gotten easier to use. Most DSLR cameras have multiple shooting modes, and even the newest of photographers can learn the automatic shooting mode quickly because the camera does all the work for you. For example, when shooting pictures on a DSLR that's set to Auto Mode, the camera uses sensors to determine the level of light that passes through to the image sensor and turns on the flash automatically in low-light situations. It has auto-focusing lenses so there's no need to worry that your pictures will be blurry. Some cameras also have built in filters or Scene Modes to ensure that depth of field, white balance, and color saturation is correct for the image you're trying to capture.

For more advanced photographers, there are manual shooting modes that allow the photographer to adjust shutter speed, depth of field, and much more. The lenses on DSLR cameras can also be adjusted from auto-focus to manual-focus to allow for greater control over how a photographer chooses to focus on any part of an image.

Some DSLR cameras even have a Video mode that allows photographers to capture high-quality video in addition to capturing images.

The Cost of DSLR Cameras

Price is probably one of the greatest reasons that DSLR cameras are popular. The first DSLR camera introduced (1991, Kodak DCS-100) was priced at around $13,000. But as the format has grown in popularity, the price has dropped. Entry level DSLR prices start at around $250-$300, depending on the manufacturer, the quality of the camera, and the number and type of lenses included with the camera body. Higher-quality, professional grade DSLR cameras can still cost upwards of $5,000 or more, and specialty lenses can cost double that.

For the average photographer, however, a reasonably priced DSLR camera will provide all the shooting capabilities needed to easily capture great family and vacation photographs. And buying used camera lenses can help keep the cost down while expanding your camera's capabilities.

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