Digital Camera Home > Five reasons you need a digital SLR

Five reasons you need a digital SLR

by Shawn Barnett
Posted: 11/20/07

I'll start out by saying that not everyone needs a digital SLR, but if you were attracted to this article, chances are you've been seeing more digital SLRs out there and have wondered how owning one might improve your photography.

What does an SLR have that your digicam doesn't? That's an important question, because SLRs are a little more expensive, bigger, and heavier than the average digicam. And you can often get more zoom and resolution in a slim pocket camera than the average consumer digital SLR kit offers. So what's the benefit?

The answers are simple, but not obvious if you haven't owned an SLR before. I've narrowed them into five categories. Put simply: Digital SLRs are faster, work better in low light, have better optics, are more versatile, and yet are very simple to use. That last item is less a reason than a reassurance. People are too often intimidated by an SLR. Even the name, which stands for Single Lens Reflex, sounds scary. But modern technology has made the digital SLR camera as easy to use as a point-and-shoot digicam.

SLRs are faster

Canon Digital Rebel XTi
With a full-autofocus shutter lag of 0.2 second, the Canon Rebel XTi is among the faster digital SLR cameras on the market. It also has an excellent AF system that's good in low light, is capable of up to 1/4,000 second shutter speeds and capturing three frames per second. It's great in low light, and in brighter light its images are stunning. See our review of the Canon EOS Rebel XTi.

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If you've owned a "regular" digital camera (I'll call them digicams), you've experienced the disappointment of looking at the LCD, seeing a great moment, pressing the shutter button and emphatically not getting what you saw on the LCD. That cute smile turned to a frown, or the child turned his head, or left the room altogether. Had the camera taken the shot when you pressed the button, you'd have had the greatest picture! That's called Shutter Lag. All cameras have it to some extent, including SLRs; but digicams are generally slower.

There are several elements to the shutter lag problem.

Human lag. The first delay actually starts with you. It takes time for the message to travel from your brain, down your arm to your finger, and then the muscle has to contract and press the button. This lag obviously isn't the camera's fault, but with you already lagging, you need all the help you can get from your camera.

Display lag. Most people don't think about it, but it takes time for your LCD to display what's happening in front of your lens. If you're looking at the LCD, you're seeing exactly what you'll capture, but with a slight delay.

Look through the optical viewfinder of an SLR, however, and you're getting the actual light through the actual lens that your camera will use to take the picture, straight into your own eye at the speed of light. No waiting. You can't get faster than that.

Shutter lag. When you press the shutter button, today's modern digital cameras go through quite a dance, usually in less than a second. They look at the scene and try to find the most likely subject, then they move the lens to find the greatest contrast to set focus, then they set the exposure, and finally take the picture. If the flash is on, they first fire a preflash to check the exposure, and then they take the picture. It's really quite amazing, because the computer technology in these cameras is achieving in under a second what used to take photographers many years to master, and many seconds, sometimes minutes to set; especially flash exposure. But when you want the shot, you want all of that to happen as fast as possible, and SLRs have a speed advantage.

Focus lag. By far the longest lag time is due to the camera's attempt to interpret the scene and find focus. I won't go into all the details about how the two different methods work, except to say that digicams use a very effective method called contrast detect, and SLRs use an older method called phase detect, which is usually quite a bit faster. Phase detect is more like the old SLRs used to use, where you turned the focus ring until two parts of the image matched up in a split-prism in the viewfinder. Most SLRs are a good deal faster at phase detect than digicams are at contrast detection. We test the autofocus lag here at, and the difference is usually significant, taking about half to three-quarters of a second on most digicams and more like one-quarter second or less on SLRs.

Zoom time. As I was preparing to write this, I asked my nine-year-old daughter why she would want a digital SLR instead of her digicam. Once I explained what an SLR was by waving the one I was holding, she blinded me with the lightbulb that went on over her head: "Oh, so I can zoom without having to press a button and wait." That's my girl. She learned that by using Dad's digital SLR, not by anything I've told her.

Indeed, the motorized zoom mechanism has to be one of the slowest elements of a digicam. Worse, most only move in broad steps, and the framing often changes once you stop zooming and try to focus. It can be quite maddening, so much so that I often zoom with my feet at that point, stepping back or forward a little to get my framing just right. With an SLR's zoom lens, zoom is mechanical, so you can fine-tune your framing with both speed and precision by just turning the lens barrel.

Shutter speeds. Of course, shutter speeds are also faster with a digital SLR, with most delivering either 1/4,000 or 1/8,000 second maximum shutter speeds, which allows you to better freeze action. It also lets you shoot at wider apertures in bright daylight, to decrease the depth-of-field and isolate your subject from its background, which is great for sports or portraits. Most digicams max out at 1/2,000 second, many at 1/1,000 second.

Finally, many external SLR flash systems will allow you to sync your flash all the way up to 1/8,000 second by pulsing rapidly during the exposure (called FP mode), which again allows for fill flash with blurred backgrounds in broad daylight.

Shot-to-shot speed. Most digital SLR cameras are capable of capturing at least three images per second, provided the shutter speed is fast enough. Higher-end cameras can do five, six, and even eight frames per second. Most digicams can deliver between only one and two frames per second at their full resolution. It's not a big deal until you're trying to capture action, but an SLR is what you need for action photography because if its superior speed in so many ways.

SLRs work better in low light

Canon EOS 40D
The 40D's full-AF shutter lag is even better than the XTi, at 0.128 second. But the big story is the 40D's low light performance. We haven't seen many cameras that will focus in the lowest light levels we test at, and the 40D's high ISO image quality is tough to beat. It has a Live View mode for composing with the LCD if you choose, and can fire at 6.5 frames per second. The 40D is shown here with the 28-135mm IS kit lens, an image-stabilized lens that is quite a bit better than most kit lenses. There are so many other impressive features on the 40D, we recommend that you see our review of the Canon EOS 40D for the full story.

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Though cameras are tasked with preserving our memories, they don't see in quite the same way that we do. Our brains work with our eyes to compensate for changes in light, both the color of the light and its intensity; and because what we see is more like video than snapshots, our brain can work to fill in details with images captured over time, while a camera has only one short moment to work with. So it's really no surprise that people are disappointed when they can't seem to get their expensive new digital camera to take a decent picture at their son's wrestling match. It sure seems bright enough in there, but unless you get to within eight feet and use the flash, what you come away with will be yellow and blurry.

The truth is that your camera is doing the best it can in a very low-light situation (something you'll know for sure if you step out from the gymnasium and into a bright, sunny day: your eyes adjust quickly, but those first few seconds really hurt). And here is where an SLR has it over a digicam: its sensor is much bigger than the tiny sensors in most digicams, which means it's going to be better in low light.

Light Sensitivity. A bigger sensor makes for bigger pixels. Bigger pixels mean more light can hit each pixel, and the camera can make a better decision about what color and intensity to assign each pixel when it builds the final image. In other words a digital SLR camera can gather more light, more quickly, and with less error than a small digicam can. All of which adds up to a better, more detailed shot of your son in the stadium, your daughter at the recital, and your family in the living room. You'll still have to hold very steady, maybe use a stabilized lens, and shoot a lot of pictures to avoid blur, but you'll have much better chances with an SLR for just about any kind of sports or entertainment photography than you do with a digicam.

Autofocus. Most digital SLRs can also focus better in low light, thanks to their dedicated AF sensors. Digicams usually use the image sensor to do their contrast-detect autofocus. In low light, we know that each of these tiny pixels is already struggling to gather enough light to determine what it's seeing, so the autofocus system has less information to work with when running its contrast-detect function.

Optics. Because it's an SLR, you can gain speed by attaching a "fast" lens. This is a lens with a lot more light gathering ability than most kit lenses. You can tell a fast lens by its maximum aperture number, usually stated right after the focal length. The closer the number is to 1.0, the faster it is. A 50mm f/1.8 lens has four times the light gathering power of an f/3.5 kit lens.

Faster lenses can cost a little more, but they really help you get the shot. With that 50mm f/1.8 lens, for example, you can shoot at an easily hand-holdable 1/60 second, whereas your f/3.5 kit lens would demand a very difficult-to-hold 1/15 second when set to 18mm. Zoom in to match the 50mm's focal length, and the maximum aperture would increase to f/5.0 and require 1/8 second. Most digicams have this same problem, where the lens's light gathering ability decreases as you zoom, and even more if you add accessory lenses. But digicams don't give you the option to change lenses completely as you can with an SLR. Which brings me to my next point:

SLRs give you a choice of optics

Olympus E-510
One of Olympus's best camera designs to date, the E-510's best feature attaches at the mount. It's the lens. Olympus has long been touting their "designed for digital" lenses, and now they have a platform to show them off. We've been testing their lenses in the lab, and we're pretty impressed. As for the E-510 itself the controls are great, the prefocus shutter lag is very good, and the high ISO performance is competitive. It has one of the first Live View modes I've found useful, and its in-camera image stabilization works pretty well. For more, click to read our review of the Olympus E-510.

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There actually are a few digicams out there with really stellar optical quality; a very few. But most digicam lenses are built with 4x6-inch snapshot in mind, not a larger, 16x20-inch print made from a crop of the original image. Unfortunately, most digital SLR kit lenses aren't built much better. The beauty of interchangeability is that you can choose whatever lens you want. In most cases you don't even have to buy the kit lens.

You can select from any number of lenses in each company's lineup, or pick lenses from among the major third-party manufacturers like Sigma, Tamron, and Tokina.

Regardless which brand you choose, you can build a set of lenses for the types of photography you prefer. Many opt for what we call a "vacation lens," one that meets all your needs in one optic. For most modern digital SLRs a typical choice is an 18-200mm lens, which covers just over an 11x zoom range. Optical quality isn't the best, though, so results are better limited to 8x10 in size, with little cropping. Your results may vary. I think a blend of a short zoom and a long zoom is better. Like an 18-70mm and a 70-200mm lens. You'll have to change lenses, but you get better optical quality, which is a big part of why you're buying an SLR in the first place.

For even better optical quality, you might want to check out some prime lenses (single-focal-length lenses). These used to be quite common, coming as the kit lens with every SLR back in the old days, but the zoom is all most shoppers consider these days. I encourage most photographers to get at least one prime lens, because they challenge you to get more involved in your subject and make the best of a single focal length, rather than just zooming. They force you to think. And if the prime you have on is not the right lens, you have to take the time to change lenses and think some more. Thinking is what separates the photographer from the snapshooter, and that's something else an SLR can help you do.

SLRs are more versatile

Nikon D80
For a solid photographic tool, look no further than the Nikon D80, whose small, tight build is just right for just about all hands. The real master stroke is the 18-135mm kit lens, which offers a perfect focal length range for nearly every kind of photography. It works well with Nikon's impressive Creative Lighting system, remote-controlling any number of flashes for unique and powerful control of lighting. That's just one way you can use the Nikon D80 to explore Nikon's vast camera system. It's a great digital SLR camera to grow with. To see our full review of the Nikon D80 click here.

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Versatility is a matter of perspective, of course. Digicams have their own claim to versatility, with most able to shoot video, and some can even record audio-only. You can't do either with most SLRs, at least not as of this writing, but an SLR opens you to a world of options to improve your still photography. Accessories like flashes, battery grips, WiFi radios, lens hoods, filters, diffusers: all can help you control your camera, and control light, better than you ever could with most digicams; and those few digicams that can work with various accessories still have nothing like the lens options available for an SLR.

Some get into SLRs just for the love of gadgets, but for most of us it's about making better pictures. With an SLR, you get the camera you need with a quick lens or accessory change. If you need better pictures indoors, you can add a bounce flash, raise the ISO, or attach a faster lens; or do all three.

Once you pick an SLR, you've bought into that system, so it's important to consider more than just the camera body. All of the major systems from Canon, Nikon, Olympus, Panasonic, Pentax, and Sony are fairly comprehensive, with most of what the average budding photographer will need, but you'll find more lens options in the Canon and Nikon lines than the others.

In some cases it's important to check that your camera will be as compatible with the system in question as you'll need. One of my favorite SLRs for consumers is the Nikon D40, but its lens selection is limited to the latest electronic AF models; and among those there are no short fast prime lenses. It's a limitation you may or may not care about, so plan carefully to match the system to your projected purposes.

SLRs are easy to use

Nikon D40
As I've mentioned, the Nikon D40 is my pick for the easiest digital SLR camera to learn and use. The Canon XTi is close, but it's tough to beat the Nikon D40's simple interface, excellent controls, and gentlemanly manners. The D40x is good, too, but I still give the D40 more respect for its excellent low light performance and better control over contrast and color. See our full review of the Nikon D40 for more.

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You'd have to spend some serious cash on a digital SLR to get one that's hard to use. I'm talking about one of the professional cameras from Canon or Nikon. All the rest of the SLRs from all the major manufacturers have several full-auto modes that will make your photography as easy as any point-and-shoot digicam. All you have to do is zoom, compose, and fire. Point and shoot.

Add all of the above factors to this last one, and you'll see that you can have all the benefits of a digital SLR -- namely better pictures -- without having to know a thing. As my daughter pointed out, digital SLRs are even simpler than digicams in many ways, able to zoom with a twist of the wrist, rather than the long, persistent press of a tiny button. You also get lower shutter lag, better images indoors, more lens and lighting options, and you can customize the camera to be just what you need with the addition of a lens or flash.

All of these factors have led me to carry a small SLR with me wherever I go, instead of a pocket camera. My images are better, and I enjoy my photography more. As I said at the outset, I won't say that a digital SLR is for everyone; no camera is. But if you're looking for greater speed and better quality images with little effort, you need a digital SLR.

For a few digital SLR cameras worth looking at, visit's Dave's Picks section.

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