If you want to upgrade from smartphone or point-and-shoot cameras to an interchangeable-lens camera, you have two main choices: DSLRs or so-called "mirrorless" cameras. Both of these camera types do essentially the same thing, but each type has its strengths and weaknesses.
Single lens reflex (SLR) cameras have been around for more than a hundred years. Like their film-based predecessors, today's digital SLRs (DSLRs) use a mirror to divert the light from the lens into a viewfinder so you see exactly what the camera sees. When you take a picture, this mirror flips up out of the way, a shutter in front of the image sensor opens, and the sensor captures the image.
Mirrorless cameras, as the name suggests, don't need a mirror. Instead, the light passes through the lens and falls right onto the image sensor, as it does in point-and-shoot and phone cameras. To preview the image before you press the shutter button, you look at a screen on the back of the camera.
So which is better Here are the seven quality measures for cameras, how the two types compare and the winner for each category:
Size & Weight
DSLR camera bodies are comparatively larger, as they need to fit the mirror and shutter mechanisms. At the moment, the smallest and lightest DSLR available is the Canon EOS Rebel SL1 ($750), which weighs 22 ounces (0.6 kilograms) with the included zoom lens attached. And that's a rather pricey camera for a first-time buyer. A more-economical model, Canon's EOS Rebel T3i ($550), weighs 25.3 ounces (0.71 kilograms) and is 3.1 inches (7.9 centimeters) deep with lens. A midrange model like the Nikon D7100 weighs 2.7 lbs. (1.2 kg) or more, depending on the lens.
Without a mirror or shutter mechanism, a mirrorless camera body can be smaller than a DSLR, and the construction is simpler. A typical mirrorless camera like the Olympus PEN-EPL5 ($549) weighs just less than 1 lb. (0.45 kg) and is less than 3 inches (7.6 centimeters) deep, including the lens.
Winner: Mirrorless camera
DSLRs use the mirror mechanism to divert light into a dedicated sensor that employs a process called phase detection. The sensor measures the convergence of two light beams to quickly snap the lens into focus.
Because they lack a mirror system, most mirrorless cameras must use a slower technique, called contrast detection — the same method used by point-and-shoot and phone cameras. The image sensor captures a small part of an image, tests how sharp it is, and then refocuses the lens and tests it again until it gets the focus right. Contrast detection is especially slow in low light and with moving subjects, as the movement confuses the camera.
Recent mirrorless cameras, like the Olympus OM-D EM-5, have faster processors that can detect the contrast more quickly, so they focus nearly as quickly as DSLRs in most conditions, but still struggle in low light. Going a step further, the Olympus OM-D E-M1 camera ($1,400; body only) uses a single sensor that combines both contrast and phase detection. Sony has also introduced a combo focus system on its new mirrorless cameras: the A7 ($1,700; body only) and A7R ($2,300; body only). But it's still not clear how well these new models will compare.
The upside of the DSLR viewfinder is that you can see the image directly, previewing exactly what the image sensor will capture.
The downside of mirrorless cameras is that they have to capture a preview of the image to display on the LCD screen. This preview can often be jerky or hard to see, especially on a cheap LCD in bright daylight. In low light, the preview can appear grainy.
Some mirrorless models mimic DSLRs by embedding a small LCD screen in what's called an electronic viewfinder. These are built into some more-expensive mirrorless cameras (such as the Panasonic GX7) or are available as add-on extras for others.
All modern removable-lens cameras include image stabilization, in which the camera reduces the blur in photos (generally at slow shutter speeds) by compensating for your shaky hands. Most interchangeable lens cameras, especially DSLRs, do this by shifting a small part of the lens. Others shift the image sensor, which enables image stabilization with any lens, even vintage models. Some mirrorless cameras can shift both a lens element and the image sensor — a combination that can be more effective than either of these methods alone. The differences between most DSLR and mirrorless image-stabilization systems are minimal.
Early mirrorless cameras used to offer lower-quality images than DSLRs, with more noise (graininess) and worse color, because they used smaller image sensors that captured less light. But the manufacturers of mirrorless cameras have found ways to reduce the noise, using better (and often bigger) sensors and better image processors, and now there is no noticeable difference in image quality in most consumer models. High-end DSLRs use very large sensors called "full frame" sensors that have given them an edge at the high end. Sony's recent introduction of mirrorless cameras with a full-frame sensor, the A7 and A7R, could be an important step in closing the quality gap, even for high-performance cameras.
Image & Video Playback
When it comes to showing an image you have just captured, both camera types can use either their LCD screen or an HDMI output to your television. Although the bodies of mirrorless cameras are smaller, most have the same 3-inch LCD screen size commonly found on DSLRs.
Lens & Accessories
If you are looking to purchase a new interchangeable-lens camera, you are buying into an entire ecosystem of lenses, flashes and other accessories that go with it. You can't use a Micro Four Thirds lens on a DSLR camera body, for example. So, when choosing a camera, you need to consider the range of lenses available for it.
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Choosing a DSLR gives you access to a plethora of lenses — from a number of manufacturers — ranging from cheap and satisfactory to professional and wildly expensive. By contrast, most mirrorless models take only a small selection of lenses from the camera maker. The only lenses for Sony Alpha NEX cameras are from Sony itself, for example. However, Sony has just announced five new lenses for its new full-frame mirrorless cameras, which considerably expands the range of lenses available.
The proprietary mirrorless systems from manufacturers like Pentax (Q cameras) and Samsung (NX series) have the fewest lenses, because these companies have only recently introduced mirrorless models. Micro Four Thirds mirrorless cameras have the widest selection because they have been around the longest and are made by several companies — Olympus and Panasonic make the cameras, and lenses are made by Olympus, Panasonic, Sigma, Tamron and others.
You can generally purchase adapters to use DSLR-size lenses on a mirrorless camera. But that often comes at a price of altering the focal length (zoom) and sometimes disabling functions such as autofocus.
The top pick for you
So, which camera type is the best pick overall? That depends on your priorities. If top image quality and speed are most important for you, regardless of weight or bulk of the gear, choose a DSLR for its superior performance and wider range of lenses.
But most mirrorless cameras have enough lens options for most shooting situations, and focus speed is improving. Therefore, mirrorless cameras are the best choice if you want to take a camera everywhere and not get weighed down along the way.