For years, 35mm SLRs (single-lens-reflex) cameras were the tools of choice for professional and serious amateur photographers for their performance, versatility, through-the-lens viewing and wide range of available lenses. When the tide shifted from film to digital in the early 2000s, the same users switched to DSLR (digital single-lens-reflex) cameras.
While DSLRs offer a number of benefits, and are still the tools of choice for pro action photographers, they also have some big drawbacks. For one, they’re complicated devices, requiring many moving parts that must be precisely aligned (notably in the moving SLR mirror assembly and phase-detection AF system). For another, they’re bulky—none will fit in a pocket, and pro models can be too much for many users to lug around all day. And with the complexity comes cost—SLR mirror assemblies and prism viewfinders are costly to produce as well as tricky to align perfectly (and keep aligned with hard use).
In 2008, a new breed of camera appeared on the scene: the mirrorless interchangeable-lens camera. It did away with the complex and bulky DSLR mirror and prism finder, replacing both with an effective and more economically produced electronic viewfinder (in the “mini-DSLR”-style cameras), or just using the external LCD monitor (in the “flat” compact-camera-style models). Doing away with the SLR stuff also made it possible to reduce camera bulk considerably: Sony’s full-frame 24-megapixel a7 encompasses just 47% of the volume of the most recent DSLR containing a similar sensor, the full-frame 36-megapixel a7R just 36% the volume of the most recent DSLR to feature a similar sensor. And those DSLR bodies are 36% and 98% heavier, respectively.
Sony Alpha a6000
Sony’s full-frame mirrorless interchangeable-lens cameras (the a7 series) feature Sony’s ½-inch 2.4M-dot XGA OLED Tru-Finder electronic viewfinders, with quick refresh rates and the ability to display a histogram. The APS-C Sony Alpha a6000 features a 0.39-inch 1.4M-dot Tru-Finder. Some action photographers who grew up with film SLRs prefer the SLR optical viewfinder, but many of today’s photographers prefer the eye-level EVF because you see in it the actual image produced by the sensor, including exposure and white balance and in-camera effects, and it can display more information, including histograms.
The absence of the mirror box also means the mirrorless cameras can be much thinner, from lens mount to sensor, than a DSLR. This offers two major benefits. First, wide-angle lenses for the mirrorless models can be of the more efficient symmetrical type, while DSLR wide-angles must be of the more complex retrofocus type. Second, you can use almost any lens for which an adapter can be found on the mirrorless cameras, while the thicker DSLRs position many non-native lenses too far from the image plane to focus out to infinity.
Mirrorless bodies are much smaller than equivalent DSLR bodies. But the lenses have to be big enough to cover the big sensors, so the lenses don’t see as much size reduction as the bodies. But the mirrorless lenses are still smaller than their DSLR counterparts, and that adds up when you’re talking about a system, including body and multiple lenses. You can pack a mirrorless system in a smaller bag, and it’s easier to carry around than an equivalent DSLR system.
Because mirrorless cameras are in Live View mode all the time, they drain batteries more quickly than DSLRs. But it’s easy to carry spare batteries. Some mirrorless models have available accessory battery grips, which, as with DSLRs, provide additional battery power, as well as a second set of controls for more comfortable vertical-format shooting.
The a7S employs the same high-precision Fast Intelligent AF system as the a7R (with the contrast-based system’s sensitivity improved to EV -4 in keeping with the camera’s low-light capabilities).
In terms of image quality, mirrorless cameras have equaled DSLRs (maybe even surpassed), in many cases, using the same sensors. The Sony a7S received the highest score ever (as of this writing) in DxOMark.com’s low-light/high-ISO ratings. Sony’s full-frame and APS-C mirrorless cameras rank right up there with the best DSLRs in terms of image quality.
Sony’s SLT-A77 and A77 II feature Sony's revolutionary Translucent Mirror Technology for fast phase-detection AF.
In terms of AF performance, the contrast-based AF systems in mirrorless cameras offer a number of advantages. Because they read contrast right off the image sensor, they’re more accurate than DSLR phase-detection systems, which rely on the precise alignment of a number of moving parts. Many of the mirrorless AF systems can operate in dimmer light than DSLR systems require. Mirrorless camera contrast-based AF systems are also much quicker than the contrast-based systems used by DSLRs when in Live View/Video modes. The one place where DSLRs still hold an edge is quick-moving action subjects with supertelephoto lenses: If you specialize in birds in flight or pro sports photography, you’re still better off with a higher-end DSLR like Sony’s SLT-A77 II, which can focus-track moving subjects at 12 fps and has available 300mm ƒ/2.8, 70-400mm ƒ/4-5.6 and 500mm ƒ/4 lenses. But mirrorless isn’t far behind: The Enhanced Fast Hybrid system in Sony’s Alpha a6000 APS-C mirrorless camera uses 179 phase-detection AF points to quickly establish focus, then 25 contrast-based points to fine tune it, very rapidly—the camera can focus-track action at 11 fps!
All of the a7-series cameras feature a built-in XGA OLED Tru-Finder eye-level electronic viewfinder, as well as a tilting 3.0-inch, 921K-dot LCD monitor.
Sony was the first to bring out a full-frame pocket camera in 2012 (the 24.3-megapixel Cyber-shot RX1), and in 2013, the company introduced the first full-frame interchangeable-lens mirrorless models, the tiny Alpha a7 and Alpha a7R, all featuring Sony Exmor CMOS sensors. The 24.3-megapixel a7 is a great general-purpose camera with quick hybrid AF, while the a7R, with 36.4 megapixels and no blurring AA filter, is aimed at those requiring the utmost in resolution. In 2014, Sony extemded the a7 series with the Alpha a7S, which features a similar compact body, but incorporates a new 12.2-megapixel, full-frame Exmor CMOS sensor that features a very wide dynamic range and excels in low light, with a standard ISO range of 100-102,400, expandable to 50-409,600. Normal ISO range for the a7 and a7R is 100-25,600. The newest a7-series camera is the recently announced a7 II.
All of the a7-series cameras feature similar 5.0x3.7x1.9-inch bodies, weighing 14.4 (a7R), 14.7 (a7) and 15.7 (a7S) ounces. Each has a built-in XGA OLED Tru-Finder eye-level electronic viewfinder, as well as a tilting 3.0-inch, 921K-dot LCD monitor. So you get convenient eye-level viewing for stills and video when you want it, and easy odd-angle shooting via the external monitor when you need that.
The a7S employs the same high-precision Fast Intelligent AF system as the a7R (with the contrast-based system’s sensitivity improved to EV -4 in keeping with the camera’s low-light capabilities). The a7 features Sony’s Fast Hybrid AF, which combines on-sensor phase- and contrast-detection AF for improved performance on action subjects. Shutter speeds range from 30 to 1/8000 seconds, plus B.
The absence of the mirror box also means the mirrorless cameras can be much thinner, from lens mount to sensor, than a DSLR.
Featuring full-pixel readout 4K and HD video at 24p and 30p, the new a7S is the “king” of the a7 series for video, its sensor and BIONZ X image processor able to process data from all of the sensor’s pixels with no binning or line-skipping, resulting in better video quality, free of aliasing, moiré and false-color artifacts (note that 4K must be recorded to an optional third-party external recorder; it can’t be recorded to the memory card). All three a7 models can record full HD 1920x1080 video directly to a memory card at 60p, 60i, 30p or 24p.
Built-in WiFi and NFC make wireless connection to smart devices easy. The FE lens mount accepts Sony E (APS-C) and FE (full-frame E) optics. The a7 cameras can also use Sony A-mount (DSLR) lenses via adapters (the LA-EA4 provides phase-detection AF with A-mount lenses) and a wide range of non-native lenses via third-party adapters.
Sony has long partnered with famed lensmaker Carl Zeiss to create high-quality optics designed for Sony digital cameras. This continues with the FE-mount lenses for the a7-series full-frame mirrorless models. Currently, there are four full-frame FE Zeiss lenses: Vario-Tessar T* FE 24-70mm ƒ/4 ZA OSS, Sonnar T* FE 55mm ƒ/1.8 ZA, Sonnar T* FE 35mm ƒ/2.8 ZA and the new Sony Vario-Tessar T* FE 16-35mm ƒ/4 ZA OSS. There are also two Zeiss lenses for APS-C Sony mirrorless cameras: the Sonnar T* E 24mm ƒ/1.8 ZA and the Vario-Sonnar T* E 16-70mm ƒ/4 ZA OSS. T* refers to an especially effective multicoating that minimizes flare and internal reflections, and Sony is the only camera manufacturer to offer Zeiss lenses with autofocus capability. OSS means the lens contains Sony’s Optical SteadyShot image stabilization (unlike its DSLRs, Sony’s mirrorless cameras don’t have sensor-shift SteadyShot INSIDE stabilization that works with all lenses). ZA means the Zeiss lens features a Sony A mount. E means Sony’s APS-C E mount; FE means Sony’s full-frame E mount.