What Is An SLR Digital Camera?

No doubt you've seen those big, sophisticated-looking cameras that professional photographers and hard-core enthusiasts use. Perhaps you've heard the term "SLR" and know that it refers to those big cameras. But what exactly is an SLR camera, and how is it any different (besides being so bulky) from the little digital cameras many people carry around in their pockets?

This article will introduce you to SLR cameras, specifically digital SLRs. We'll help you understand what these technical marvels can do and why you may—or may not—want to invest in one.

What is an SLR Camera?

SLR stands for "Single Lens Reflex," and it refers to a class of cameras. Other examples of camera classes would be "Point and Shoot" (P/S) cameras, "Prosumer" cameras, integrated cameras (like in cell phones), pinhole cameras, etc. While there are many variations among SLR cameras, they all have a couple of important things that make them part of the SLR class.

First, unlike P/S cameras, SLR cameras have two distinct, detachable parts: a body, and a lens. The body, also called a "back" by photographers, contains the brains and the controls of the camera. If it’s a traditional SLR camera, film’s contained in the body and is exposed behind a mechanical shutter. If it’s a digital SLR (a.k.a., a DSLR), the film’s replaced by a sensor chip which—like the film in a traditional camera—is also exposed behind a mechanical shutter.

Along with the body, the other component of an SLR camera is the lens. The lens can be removed from the camera and swapped with other lenses. More on why you might want to use different lenses later.

The other distinct SLR characteristic relates to how, specifically, the picture is captured. With P/S digital cameras, the shooter lines up the shot by watching a live video image on the LCD. Alternately, some P/S cameras also have a tiny optical viewfinder above the LCD that can be used to line up the shot.

The key limitation to both of these methods is that the shooter isn't seeing exactly what the camera's lens is seeing. In the case of the LCD, the shooter’s seeing a video rendering of what the lens sees. In the case of the optical viewfinder, the shooter is looking through a completely separate mini-lens. If you have a P/S with a viewfinder, try covering the main lens with your hand or a lens cap and you should still be able to see through the optical viewfinder.

So how is an SLR camera different? With an SLR, the photographer actually lines up the shot by looking through the lens. Take a look at the diagram below:

When the photographer is framing the shot, light is directed through the lens. It hits a mirror and is reflected up toward the viewfinder. As a result, the photographer’s looking right down the barrel of the lens and sees the exact shot that will eventually be captured. The term for this phenomenon is "WYSIWYG" (pronounced "WHIZ-EE-WIG") which stands for "What You See Is What You Get". When the photographer presses the shutter button to take the picture, the mirror flips up and out of the way of the sensor (making a mechanical "click" noise), the shutter opens, light strikes the sensor, and the picture is taken.

So we've established that detachable lenses and WYSIWYG viewing are characteristics of an SLR camera. So what? Why are those good things?

Why Might I Want an SLR?

The primary reasons for owning an SLR are quality and flexibility.

From a quality standpoint, the bigger body of an SLR camera holds a larger photo sensor than a digital P/S camera. That larger sensor area leads to cleaner image capture because of decreased interference or "noise" on the sensor. For that reason, an 8 MP P/S camera is not the same quality as an 8 MP DSLR, even though they capture the same number of pixels.

Beyond the size and quality of the sensor itself, the SLR improves potential picture quality by giving the photographer more control over how the image is captured. Everything from depth of field to white balance to flash power to metering mode can be controlled by the photographer. For those interested in learning photography, having the ability to control these parameters is invaluable.

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In terms of flexibility, SLR cameras are in a class by themselves. Different lenses can be used depending on what the photographer hopes to capture. For landscape photography, a zoom lens with good wide angle range is helpful. To capture objects that are far away, a telephoto should be used. A macro lens can be used for close-up photography. Certain lenses specialize in low light conditions (ever wish you could take a "natural" picture in low light without the washed out look from a flash?)

The accessories for SLR cameras don't end with lenses. SLR photographers can take advantage of high-quality flash units for more natural looking flash photography. They can mount filters over their lenses to remove glare or affect color tone or use remote controls to control their cameras from a distance.

The best way to think of an SLR is as a camera system, not just a camera. The beauty of all these accessories is that they work with other camera "backs" that are part of that system. For example, I bought a cheap Canon EOS SLR film camera shortly after I finished college. I also purchased a lens and an external flash for that film-SLR camera. When I finally decided to go digital, I chose to get a Canon EOS DSLR. Because I stayed within the Canon EOS system, the lens and flash that I'd used with my film SLR now worked with my new digital SLR. I've recently moved up to my second Canon DSLR and all the accessories I had from the previous two cameras now work perfectly with my new camera. As technology changes, I'm able to replace parts of my system without having to start over again.

Beyond the quality and flexibility aspects of SLR cameras, there’s a host of additional features that make SLRs great cameras. Here are a few of the better features found on most SLRs:

  • Instantaneous Shutter Release: With many P/S digitals, there's a brief delay between when you press the button and when the picture is captured. If your subject isn't holding perfectly still, you may miss the shot. On an SLR, however, the picture is taken instantly when you press the button.
  • Better Controls: All those buttons on an SLR may look confusing, but once you learn them, you'll be able to quickly change camera settings without even looking at the camera. On P/S cameras, many camera controls are buried in menus, so it takes longer to make camera adjustments.
  • Manual Focusing: Most of the time you'll be able to use auto-focusing. In those situations where auto-focus isn't getting the job done, however, you'll be able to switch to manual focus if you have an SLR.
  • Aperture and Shutter Control: With SLR's (and some high-end P/S cameras), you can adjust aperture size and shutter speed. This gives you control of depth of field (i.e., how much of the scene is in focus) and allows you to freeze (or blur) motion.
  • RAW Files: Most P/S digitals only capture pictures as JPEG files. This limits your ability to edit the picture after the fact. Most DSLRs give you the option to also record your pictures in a RAW file format. RAW gives you flexibility to adjust color, exposure, and white balance on your PC after the picture has been taken.
  • Greater ISO Control: Digital SLRs generally have a wider ranger of ISO settings than P/S digitals do. Also, the quality of the picture at a high ISO setting is generally cleaner (i.e., less noise) with an SLR. For an explanation of how ISO works, check out this article.
  • Better White Balance Control: DSLRs generally have the best white balance controls, including a "custom" white balance setting. This means fewer pictures will have an unnatural color tint to them.
  • Better Exposure and Flash Control: Most P/S digitals have fully automated exposure and a simple on/off flash setting. Most DSLRs allow you to fine-tune your exposure (or meter it differently) and can incrementally adjust the intensity of the light from flash.

Why Might I NOT Want an SLR?

There are some great SLR cameras out there with killer features, but before you grab your credit card, let's consider the downside of an SLR.

First and foremost, SLR cameras are expensive. The camera backs themselves are usually several times more expensive than P/S cameras. Once you start talking about lenses and accessories, the prices really go up. The absolute cheapest lenses start at close to a hundred dollars and can go up to several thousand dollars when you get into professional lens grades. Those lenses will last a long time and have great resale value if you want to sell them, but it's still a lot of money to lay down.

Beyond the financial considerations, an equally significant downside of SLRs is their physical size. Even if you're carrying just the camera with one attached lens, an SLR’s a bulky camera that won't fit into a pocket or a purse. When I bring my full SLR system with me, I carry a very heavy backpack that contains my camera, my lenses, some filters, my flash, cleaning accessories, extra batteries, extra memory cards, etc. It can be a real pain hauling all that around. Even though I absolutely love my SLR, I recently picked up an inexpensive P/S digital for those occasions when I need the convenience of a pocket-sized camera (going out to dinner, on a boat, on a ski slope, etc.). Don’t underestimate the size factor when considering an SLR.

The last reason for possibly avoiding an SLR's the least obvious. Many people assume that more sophisticated, pricier cameras take better pictures. This isn't necessarily the case. Point and Shoot cameras make many decisions about camera settings automatically for the users. SLR cameras, on the other hand, allow many of these decisions to be made by the photographer. If the photographer doesn't know what settings to apply, a picture taken with an SLR can actually turn out worse than one taken with a P/S. If you don’t want to spend time learning how to control it, an SLR probably won’t be worth your investment.


Is a digital SLR camera right for you? To answer that question, see if either of the scenarios below describes your needs:

Scenario 1. You want a camera that can be carried in a pocket or a purse. You'd rather not spend a fortune on a camera. Ultimately, you want a camera that "just takes good pictures" without you having to mess with a lot of controls. If this is you, then you might consider a P/S camera. An SLR really wouldn't meet your needs.

Scenario 2. You're interested in learning the art of photography. You want to create photographs, not just take snapshots. You have the funds to make a significant investment in camera gear and you want a system that will grow with you as you learn. Finally, you're willing to invest the time into learning how to use your camera and how to get the best pictures from it (both during the shot and in post-process afterward). If this is you, a DSLR can be a fantastic tool to help you get the most from your photography. Enjoy!

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I have the Sony Alpha 100- well worth what I paid for it. One of the best pictures I have seen since the 35mm. Camera. It was a hefty price between 900-1k at the time- it has dropped in price. I would not recommend for the family pic only type of person. Great Camera though. When you combine with using Photoshop to edit in RAW form- the end result can be breathtaking.

I've heard good things about the A100.  How do you like the steady shot body-based stablization system?  I've always wondered how well it performs vs. a lens-based IS system like Canon and Nikon use (I have a Canon 30D, so I'm more familiar with the Canon world).

to be honest it could be better. I still get blurry shots quite a bit. Unfortunately I have not used the nikon or the canon to compare it to. I hear the raves about the D80 (my cousin has one and has sent me photos from it that are breathtaking).

I guess you kind of have to pick your poison with the stabilization thing.  You can pay for it once and get it in the camera body.  Or you can go with a potentially more effective lens-based system, but then be stuck paying a premium for each and every lens you buy.  I only have IS on one of my lenses - works great, but hits the wallet pretty hard.

Yeah, Lenses are hard to judge on. I see these offers for 1600mm lens for $250 on ebay but always wonder the quality.  Optoma I think is the MFG. You never know what you may be getting. Lenses are the one thing I am always leary about. for my Camera all konica & minolta lenses should work but then again I fear the case if it doesn't.

Yeah, you definitely have to do your homework on lenses because there is so much variation in quality.  You can't even rely on a single brand name to ensure quality either.  Canon makes some of the best lenses in the world, but some of their cheapy stuff - with the exact same monogram on the lens - is pure junk.  Before I buy, I spend a fair amount of time reading up on lenses and looking closely at samples taken (lots of great reviews on the internet these days).  Then, when I do buy, I usually buy used.  The good news is that quality lenses lose very little value over time, so if I don't like it, I can pretty easily resell it without incurring much loss.


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