SLR vs. Mirrorless

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There is a lot of hype and name-calling these days on the topic of SLR vs. mirrorless, so in this article I want to list the pros and cons inherent to both technologies as objectively as possible.

Let’s start by listing the main reactions by photographers on the topic:

  • “Traditional photographers” (usually pros and advanced amateurs) cling to their SLRs, claiming that their image quality is unsurpassed. They may be intrigued by the new (mirrorless) technology, but they have not experimented meaningfully with it yet.
  • A small but growing group have embraced mirrorless and are very happy. These used to be mostly people with little or no investment in established systems, but more and more “traditional photographers” are adding to or replacing their SLR systems with mirrorless.
  • Some “true professionals” (who care less about the tools and more about the final image and of course about revenue) are predicting the death of the SLR, but are still using one on their most demanding jobs. At the same time they’ve switched to mirrorless for everything else, including personal and commercial projects (examples: Ming Thein, Kirk Tuck, Thom Hogan).

And now here are the strengths and weaknesses of the SLRs and mirrorless technologies:

Overall SLR Mirrorless
Technology Well established, with long release cycles and less frequent updates. Large user-base including lots of professionals. Evolves rather quickly. Newer models supersede existing models about once a year. Slow acceptance outside of Asia, however users who understand the strengths of this technology find it very capable for general use.
Body size and weight Larger (has to contain the mirror box) and heavier (more hardware: two mirrors, AF sensor, viewfinder prism). Pro-level bodies are especially large and heavy. Nicely small and light. Some (but not all) models are too small, to the point of being uncomfortable to hold. Less advanced models can be made as small as compact cameras but with the advantage of much larger sensors and thus higher image quality.
Wide-angle lenses Larger and heavier (must be positioned further away from the sensor because of the mirror). Impressively light and small.
Telephoto lenses Large and heavy. Virtually identical size and weight for same size sensor, but much smaller for smaller sensors.
Accessories Cheaper since longer on the market. Generally quite expensive (unnecessarily so).
Mechanical complexity High, requires very precise alignment for best results, easier to damage or misalign, costly repairs. Relatively low.
Electronic complexity Average. High, difficult to repair after the model has been discontinued for a while.
Price Reasonably priced. Lower-end models reasonably priced. Higher-end models artificially overpriced (should be cheaper than an SLR with a comparable sensor and build quality).
Image Quality SLR Mirrorless
Sensor Large sensors (APS-C and full-frame) support either larger pixels (more dynamic range, less noise) or more pixels (irrelevant for Web usage, but important if you print very large). Either way, the sensors in SLRs enable very high image quality. Same image quality as SLR for same sensor size. Systems based around the smaller m4/3 sensors are at a (surprisingly) small disadvantage.
Lenses The best sensors (especially those with high pixel counts) require the best lenses. Many older lenses do not deliver optimal results. New lenses are generally superb but also expensive.
Image Stabilization Nikon and Canon have no IS in the bodies. Not all their lenses have IS and if they do, they are quite expensive. Sony has IS in the bodies, so all lenses are stabilized. Panasonic and Fujifilm have IS in most lenses, Sony in some, Olympus has done it right and put IS in the body, so all lenses are stabilized. Smaller sensors and smaller lenses have the advantage of having to move smaller and lighter elements over shorter distances.
Camera shake Larger sensors need longer focal lengths which require shorter shutter speeds or sturdy tripods for sharp images. Sensors with high pixel counts make the need for shorter shutter-speeds or sturdy tripods even stronger. If you don’t use a tripod (who does?), then the longer shutter speeds mean that you have to shoot at higher ISO values, which negates the advantage of lower noise. Smaller sensors need shorter focal lengths which allow longer shutter speeds before camera shake causes unsharp images. This means that you can shoot at a lower ISO and get the same sharpness and similar noise levels to larger sensors. Lighter equipment also allows you to use smaller and lighter tripods.
Viewfinder SLR / Optical Viewfinder (OVF) Mirrorless / Electronic Viewfinder (EVF)
Image clarity Nothing beats the clarity of an OVF. EVFs are getting better, but they do not (yet) match OVFs. A few additional technology iterations are needed.
Size and coverage Only the best bodies have large viewfinders and 100% coverage. Low-spec bodies (especially low-spec APS-C bodies) have low magnifications (resulting in a smaller viewing area) and less than 100% coverage (so you get more in the image than is visible in the viewfinder). All bodies have 100% coverage. Higher-end bodies have very large viewfinders (even larger than some full-frame OVFs).
Shooting information Based on pre-exposure measurements only (selected exposure, AF mode, buffer size, battery capacity, etc.). The image in the viewfinder does not reflect the brightness, dynamic range, DOF, motion blur or color rendition of the recorded image. In difficult situations the photographer needs to record and image, examine it (most importantly its histogram), then if needed change some parameters and re-shoot. Additional information is available in live-view mode on the rear screen, but this defeats the purpose of an SLR body. Shows the exact rendition of the image: matching its brightness, dynamic range, DOF, motion blur and color rendition. Can blend in a real-time histogram and blinking highlights, which allow the photographer to optimize all shooting parameters prior to releasing the shutter.
Additional features You can view and compose without turning the camera on. Bright viewfinder image even when the light is low, image magnification when focusing manually, focus peaking (highlight areas in sharp focus), image review and menu settings are possible in the viewfinder. Light entering through the viewfinder does not fool the exposure meter. On the negative side, you cannot look through the lens and compose when the camera is turned off.
Shooting video Thew viewfinder blacks out, so the rear display must be used. Both the viewfinder or the rear display can be used.
Shooting Experience SLR Mirrorless
Battery life Extremely good: even with a fair amount of rear-display usage it is possible to shoot several days on a single battery charge. Once spare battery is enough for virtually any assignment. Poor: a full battery charge typically lasts at most one day. For trips away from electric power mirrorless shooters calculate one to two batteries per day.
Auto focus Very quick in single and continuous mode. For optimal results the AF system must be well-aligned and calibrated (individually for each lens). Only advanced bodies allow AF calibration by the user. AF is quite slow in live-view mode unless phase-detect sensors are built directly into the sensor. The first body outfitted with such sensors debuted in 2013. Can be very quick and precise in single AF mode. No alignment or calibration is needed as the focus is read directly off the imaging sensor. Continuous AF and subject tracking are quite poor unless phase-detect sensors are built directly into the sensor. Several cameras with such sensors debuted in 2013.
AF sensors Placed at fixed locations, usually too close to the center of the viewfinder. The AF point can be placed anywhere in the frame.
Face recognition Not possible. Works very well. Focuses on the eyes of a person and can give preference to “registered” faces, to the left or right eye or to the eye which is closer to the camera.
Aspect Ratios Only 3:2 possible in-camera. Various aspect ratios are possible and simulated in the viewfinder.
Mirror lockup Necessary for critical sharpness at certain shutter speeds. Not needed since no mirror is involved.
Shooting noise Not very loud but still audible, due to mirror slap and shutter actuation. Older lenses with mechanical AF cause additional noises while focusing. Very quiet as noise is caused only by the shutter. Bodies with electronic shutters are completely silent. Virtually all lenses zoom and focus without audible noises.

Too much detail? Let’s summarize:

  • A camera with a larger sensor (typically an SLR) enables higher image quality (more color depth, more dynamic range and lower image noise).
  • A camera with a smaller sensor or with a shorter lens-to-sensor distance (mirrorless) can be made smaller and lighter. It will be less affected by camera shake and it will be easier to design an effective image stabilization system for it. Both of these lead to a higher image quality.
  • An SLR and a mirrorless with the same sensor have the same image quality potential. However it is a bit trickier to unlock the full potential of the SLR: make sure that the AF system is properly aligned and calibrated, choose a very good lens, achieve optimal exposure (by shooting an image, examining the histogram then modifying exposure if needed). Mirrorless requires good lenses too, but the other things are easier: the AF is always perfectly aligned and calibrated, and you can see the histogram and optimize exposure prior to releasing the shutter.
  • The optical viewfinders in SLRs show the scene being photographed exactly like it looks in real life. While this sounds appealing, it leads to unpleasant surprises about “how the picture turned out.” The EVFs in mirrorless cameras do the exact opposite: they show how the image will look when captured with the current camera settings. This allows the photographer to optimize all parameters before taking the shot.
  • An SLR uses batteries at a much slower rate than a mirrorless camera.

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And now let’s look at a few important camera models (as of October 2013) and at their claims to fame:

  • Nikon D800 – not the fastest, not the largest and not the most expensive SLR, but if used on a tripod, carefully focused and paired with the right lenses it delivers the ultimate image quality at unsurpassed 36 MP. This is the benchmark and the tool of choice for the serious working professional.
  • Canon 6D – the smallest and lightest full-frame SLR, very popular with advanced amateurs. Usually paired with the Canon 24-105/4 lens for a “light” travel kit.
  • Sony α99 – a full-frame hybrid between SLR and mirrorless. It has a fixed half-silvered mirror which makes an SLR-style AF-system possible, but since light reaches the imaging sensor at all times, the camera uses an EVF with all pros and cons listed above. The camera features built-in image stabilization, which is great and an important advantage over Canon and Nikon. The camera is well-respected in professional circles, but not many pros have abandoned their SLRs and switched to Sony.
  • Pentax K-3 – Pentax’s top-of-the-line SLR is based on an APS-C sensor. Apparently Pentax thinks that the “average (Pentax) photographer” is not willing to pay for or carry a full-frame SLR system.
  • Sony NEX – very small mirrorless cameras built around an APS-C sensor. These bodies are popular with the general public, but less so with photography enthusiasts and pros because of the lack of serious lenses.
  • Sony A7r – just released full-frame mirrorless body with virtually the same sensor as the Nikon D800. The lens choices are very limited at this time, so we’ll have to wait and see if the new system takes off.
  • Fujifilm X-Series – a mirrorless system built around an APS-C sensor and a very ambitious set of lenses. Even though some find the AF speed a bit slow, the system is very popular with enthusiasts and pros. The AF speed of newer bodies keeps getting better.
  • Micro four-thirds (m4/3) – a system created by Olympus and Panasonic, but now additional companies have joined the effort. Based on a sensor smaller than APS-C, m4/3 equipment is smaller and lighter than all listed above. Due to the smaller sensor, m4/3 equipment is inherently at a disadvantage with regard to dynamic range and image noise, however rigorous tests (Ming Thein, Thom Hogan) show that the disadvantage is quite small and counteracted to some degree by other factors (size, usability, lens quality, camera shake, etc.). The m4/3 lens system is quite complete, offering many serious and many budget choices.
  • Olympus OM-D – a series of pro-level m4/3 bodies that have attracted a very loyal following by enthusiasts and pros. Many agree that the image stabilization built into these bodies is the best on the market.
  • Panasonic GH3 – a m4/3 body, somewhat larger than the other m4/3 offerings, but recognized by many as the best general-purpose camera for recording video.
  • Panasonic GM1 – a m4/3 body as small as a compact camera but with interchangeable lenses and much better image quality (due to the “huge” size of the imaging sensor when compared to compacts).