Mirrorless Vs. DSLRs

One of the primary advantages of traditional DSLRs over mirrorless models is that DLSRs offer faster phase-detection autofocus, while mirrorless models employ typically slower contrast-detection AF that relies on the imaging sensor. However, camera makers are working to improve contrast-detection AF speeds.

Sony recently introduced a unique solution for its latest generation of NEX models: The LA-EA2 adapter not only allows you to use legacy Sony and Minolta Maxxum lenses with the newest NEX cameras, but also incorporates a phase-detection AF system based on Sony’s Translucent Mirror Technology providing faster autofocus for both still and video recording.

For many years, the two most popular types of digital cameras have been compact models and digital SLRs. Each offers advantages over the other. Compacts are small (many will actually fit in a pocket), simple and self-contained. DSLRs, on the other hand, typically produce much better image quality (due to their larger image sensors), are much quicker, accept a wide range of interchangeable lenses and have convenient eye-level, through-the-lens optical viewfinders.

Over the last couple of years, a new type of digital camera has arrived on the scene, and quickly gained popularity: the mirrorless interchangeable-lens camera. In fact, in 2011, more mirrorless models were introduced than DSLRs. Mirrorless models combine compact size with DSLR image quality, thanks (in most cases) to putting a DSLR sensor into a compact body.

The latest camera maker to introduce a mirrorless system, Nikon’s new 1 series launched with two modes, the V1 and J1. The new cameras are significantly more compact than even Nikon’s smaller DSLRs, and feature a totally new "CX-format" sensor that’s about 45% smaller than Nikon’s DX-format sensors.


A popular (but not unanimous) complaint about single-lens-reflex cameras is that they’re too bulky. Back in the early 1970s, Olympus stunned the camera industry by introducing the OM-1, a 35mm SLR that was noticeably smaller than any that had come before. So it was not unprecedented that when a consortium introduced the compact Four Thirds System in 2003, the first Four Thirds model was an Olympus: the pro-oriented E-1 DSLR.

By designing DSLRs around a smaller 17.3×13.0mm sensor (most DSLRs of the era used "APS-C" sensors, which measure around 23.6×15.8mm), the Four Thirds System creators were able to produce smaller cameras, with smaller lenses optimized for the sensors. But most Four Thirds System models were not noticeably smaller than APS-C DSLRs (largely because of their bulky SLR mirror/prism viewfinder assemblies).

In 2007, Sigma introduced the DP1, a compact camera with a DSLR sensor—the same unique Foveon X3 unit used in its DSLRs. The DP1 was a truly compact camera that produced true DSLR image quality. However, it had a fixed 28mm (35mm-camera-equivalent) lens, which limited the user to wide-angle photography. The DP2 model that followed had a built-in 41mm (35mm-equivalent) "normal" lens. These cameras are still in production, in DP1x and DP2x form.

In the same year, the Four Thirds consortium introduced the Micro Four Thirds System. Based on the same 17.3×13.0mm image sensor as the full Four Thirds System, the Micro Four Thirds models reduced camera size by doing away with the DSLR’s bulky mirror box and pentaprism or pentamirror viewfinder assembly and replacing it with an eye-level electronic viewfinder. The first Micro Four Thirds camera was the Panasonic G1, which looked like a miniature DSLR and was noticeably smaller than the APS-C (and Four Thirds System) DSLRs.

Both Olympus and Panasonic mirrorless cameras are built around the Four Thirds imaging sensor that was first introduced in 2003. Dubbed "Micro Four Thirds," the first mirrorless models from Panasonic debuted in 2007. Olympus expanded the Micro Four Thirds platform with the digital reintroduction of its noteworthy film-based PEN series cameras of the 1960s and 70s.

Mirrorless models usually have a shape and size more akin to compact zoom cameras than traditional DSLRs. While all mirrorless systems benefit from smaller lens models, Panasonic offers some mirrorless models like the new G3 that have contours reminiscent of traditional DSLRs. It’s something to consider when selecting a camera. Photographers with larger hands may prefer the grip and feel of this design.

Olympus soon followed with the E-P1, a Micro Four Thirds model with a "flat" design like the pocketable compact digital cameras. These models were followed by Panasonic’s GH1, G2, GH2, G10 and G3 (all mini-DSLR style) and GF1, GF2 and GF3 (featuring "flat" designs); and Olympus’ E-P2, E-P3, E-PL1, E-PL2, E-PL3 and E-PM1 (all 12.3-megapixel "flat" designs).

In 2010, Samsung introduced the NX10, with a 14.6-megapixel APS-C sensor in a "mini-DSLR" shape, followed by the 14.6-megapixel "flat" NX100, and the new 20.3-megapixel "flat" NX200.

Sony entered the fray that year with the NEX-3 and NEX-5—"flat"-style cameras that were the smallest mirrorless bodies yet, with Sony APS-C sensors. These were followed by the current models, the 16.1-megapixel NEX-C3 and NEX-5N and the 24-megapixel NEX-7, all with Sony APS-C sensors.

Earlier this year, Pentax introduced the Q, a "flat" body that’s the smallest interchangeable-lens camera yet—largely because it’s built around a 12.4-megapixel compact-camera-size 1/2.3-inch (6.2×4.6mm) sensor.

The most recent company to join the mirrorless interchangeable-lens world is Nikon, with two 10.1-megapixel Nikon 1 models, the V1 and the J1. These cameras feature a new "CX" format: The sensor measures 13.2×8.8mm, about halfway between compact-camera size and Four Thirds System size.


Today’s DSLRs start up and wake up from sleep mode very quickly, and there’s little lag between the moment you fully depress the shutter button to take a shot and the moment the shot is actually taken. And their phase-detection AF systems are very quick, capable of handling the toughest action subjects (in normal mode; in live-view mode, they use contrast-based AF, which is much slower). This hasn’t been the case with the compact digital cameras.

But today’s mirrorless models also are very quick. They start up and wake up more like DSLRs than like compact cameras, and their contrast-based AF systems are amazingly quick. In fact, current Panasonic mirrorless models offer "the world’s fastest level of Light Speed AF with precise Contrast AF"; new Olympus mirrorless cameras provide "the world’s fastest autofocus" (claimed to be faster than a top DSLR’s phase-detection system); and Nikon’s new 1-series mirrorless models offer a hybrid focal-plane phase-detection/contrast AF system that can work at 10 fps. A bit about AF systems: The phase-detection systems used in DSLRs split the light delivered by the lens into separate beams, and direct those onto AF line sensors. Exactly where the beams hit the line sensors tells the AF system instantly whether or not the image is in focus, and if not, in which direction it’s out of focus, and by how much. The contrast-based systems used in compact digital cameras and mirrorless cameras read contrast at the image sensor itself, but require several readings to determine whether the image is in focus, and if not, in which direction it’s out and by how much. This has made phase-detection AF systems
much faster than contrast-based systems, and much better for continuous predictive focusing on moving subjects.

Many newer mirrorless cameras feature much faster contrast-based AF systems (due at least in part to much quicker read rates), and have actually caught up to phase-detection DSLRs in AF speed. In any event, for still subjects in good light, at least, today’s mirrorless interchangeable-lens cameras can hold their own against the best DSLRs, and are way better than the compact digital cameras—and the contrast-based AF systems employed by DSLRs in live-view/movie mode.


Because many DSLRs are able to use the same lenses as the manufacturer’s 35mm SLRs, most offer a wide range of lenses. Newer lenses are designed specifically for digital imaging, and tend to produce better results. Even the relatively new Four Thirds System provides a wide range of lenses.

Mirrorless camera systems are newer, and thus don’t yet have such extensive lens lineups. But all the basic ones are there, and the mirrorless models offer an advantage over the DSLRs: Because the mirrorless models have much smaller "flange-back" distances (the distance between the lens mount and the image plane), they can use any lens for which an adapter is available. Many mirrorless camera users employ such mounts to attach Leica, Zeiss and other top lenses (although this means losing autofocusing capability).

Sony offers the LA-EA2 adapter for its newer NEX cameras. This incorporates a phase-detection AF system similar to the one in their SLT cameras, and not only permits mounting Sony (and legacy Minolta Maxxum) DSLR lenses, but provides phase-detection autofocusing with them.

One point to bear in mind is that you get DSLR image quality by using DSLR-sized image sensors. And while manufacturers have done an amazing job of squeezing big DSLR sensors into truly compact bodies, a given-sized sensor requires a given-sized lens diameter to produce an image circle sufficiently large to cover the format. Thus, while the mirrorless interchangeable-lens cameras with the largest sensors produce the best image quality, they also have the largest lenses. But the overall body/lens package is still much smaller than an APS-C (or even Four Thirds System) DSLR with equivalent focal lengths—even though it won’t fit in a pocket.


Compact digital cameras have had low-res video capability almost from the start, and a number of newer compacts and most DSLRs introduced in recent years offer HD (720) or even full HD (1080) video capability. The mirrorless cameras all offer HD video, most providing full HD. The newest Nikon, Olympus, Panasonic and Sony models offer the most advanced video capabilities, including usable continuous autofocusing while shooting, something lacking in the HD-capable DSLRs (except Sony’s Translucent Mirror models, which provide phase-detection continuous AF during video shooting). Bear in mind that built-in microphones will pick up the sound of the AF motor.

As is the case with DSLRs and compact digital cameras, the mirrorless models were designed primarily for still photography, and aren’t meant to be replacements for serious dedicated digital camcorders. But they can turn out great video clips, which adds motion and sound to your creative photographic arsenal. And their larger image sensors and interchangeable lenses provide more depth-of-field control and flexibility than the affordable camcorders.


To determine which is better for you—mirrorless or DSLR—you have to consider your own photography. As far as image quality is concerned, the top mirrorless models can match that of the top APS-C DSLRs. Mirrorless cameras are much smaller and lighter, making them easy to carry for long periods, and easy to use inconspicuously.

DSLRs are better balanced with longer lenses, and better suited for action photography. All DSLRs have convenient eye-level viewfinders, while some mirrorless cameras don’t. Mirrorless cameras that do have electronic viewfinders often aren’t as good as the finders on midrange DSLR cameras (some feel the EVFs are better than the pentamirror finders of many low-end DSLRs—check this out for yourself before buying either camera type).

The mirrorless interchangeable-lens cameras are rapidly gaining market share, and not just among casual photographers, so, obviously, they’re just what many photographers are looking for: truly compact cameras that make top-quality images.

When An SLR Isn’t An SLR

Sony A77

The traditional single-lens-reflex camera contains a reflex mirror set at a 45° angle. When light from the lens hits the mirror, it’s reflected up to a focusing screen, then on to the pentaprism (or pentamirror, in lower-cost cameras) and delivered to the viewfinder eyepiece. When you press the shutter button to make a shot, the mirror flips up out of the light path, so the light can reach the image sensor (or film, in a 35mm SLR). The mirror then drops back down to the viewing position once the exposure has been made.

Sony’s SLT cameras look just like DSLRs, and contain a 45° mirror like DSLRs. But the mirror doesn’t move. It’s semi-translucent, transmitting most of the light to the image sensor while reflecting a portion of it up to a phase-detection AF sensor. This system allows the camera to use the quick phase-detection AF system all the time—even during video recording. In fact, the Sony SLTs are the only DSLRs that provide continuous phase-detection autofocusing for video. The nonmoving mirror also does away with the SLR’s brief viewfinder blackout during exposure, and the vibration caused by the mirror flipping up and down.

Instead of an SLR’s eye-level optical finder, the Sony SLT cameras use an eye-level electronic viewfinder—a very high-resolution OLED one in the top SLT-A65 and SLT-A77 models. Historically, electronic viewfinders have not been as good as SLR optical finders, especially for action or in dim light, but the Sony OLED finder is a big step in the right direction.

Since the SLT cameras are in live-view mode all the time, that takes a toll on battery life. While battery life is less than that of a DSLR, it’s better than that of a typical compact camera, and it’s easy enough to carry a spare battery or two (something you should do with a DSLR, as well).

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