It’s been an exciting few years for cameras. A few major shakeups have changed the landscape of professional photography and we, the consumers get to reap the benefits. The biggest shift has been the rise of the high-end mirrorless camera and particularly fantastic new cameras from brands like Sony and Fuji.
During this past year, Sony became the biggest seller of full-frame cameras entirely on the strength of its mirrorless designs. This spurred Canon and Nikon to jump into the mirrorless ring with their Z and e OS r lines launching. This last fall mirrorless cameras have become a big part of the market. But, they haven’t replaced SLRs; the camera style that’s been king for nearly a hundred years.
So what exactly makes a camera mirrorless and why would you pick one style over another?
First off, let’s define some terms. SLR stands for single lens reflex and the reflex here has to do with reflections. In a reflex camera, light from the lens is reflected off a mirror, into the viewfinder; an early design- the twin-lens reflex invented in the 1880s and popularized by Rolleiflex in 1927 had a dedicated lens for the viewfinder and a second lens that was actually used. To take the picture, the challenge with these cameras along with other styles like rangefinder and point-and-shoot film cameras is that because your viewfinder is offset. From the lens, what you see doesn’t exactly line up what the camera sees. The framing of your photos will be a little bit different than how they looked through the viewfinder.
SLRs fixed this by linking the viewfinder directly to the lens. In an SLR, light enters the lens, bounces off a mirror and then into a prism, that redirects the light into your eye. Because of this, what you see will line up exactly with the photo you’re taking. But, this introduces its own challenges, because now there’s a great big mirror in the way behind the lens. To deal with this, in an SLR a spring flips the mirror upwards and out of the way, before the shutter triggers and records the photo. It then snaps the mirror back into place. These mechanisms have to move extremely quickly and be robust enough to survive hundreds of thousands of photos.
DSLRs have a lot of mechanical complexity. But, they work well enough. As cameras switched from film to digital sensors, the mir system survived. Nearly unchanged, still having a mirror does have a few drawbacks because the mirror has to get out of your way. In an SLR, your image through the viewfinder momentarily goes black whenever you press the shutter. It can also be noisy and the mirror assembly itself is fairly bulky, taking up a lot of space and making SLR larger than many other styles of cameras.
By contrast, a mirrorless camera doesn’t have a mirror. Light passes through the lens and falls directly onto the sensor; technically digital .Pointless shoots going back to cameras from Kodak, Rico and Epson. In the 90s, they were mirrorless as our pocket cameras, like the Nikon cool picks or Sony cybershot. These days, however, when someone refers to a mirrorless camera, they usually mean a mirrorless interchangeable-lens camera. One result of not having a mirror is that you can’t look directly through the lens.
You have to rely on digital view finders. This is essentially a video preview from the sensor displayed on screen. Now these have gotten a lot better. But, they used to be pretty low resolution or have bad delay between the real world and what’s on your screen because your viewfinder is a so-called live view. Straight from the sensor, you see what the camera sees. So, you don’t need to worry that your view will be different from the final shot. This ends up being pretty similar to how dslr’s work. Autofocus is a different story, though how autofocus works is one of the biggest differences between DSLRs and mirrorless cameras.
In the past, good autofocus has actually relied on having a mirror and DSLRs ability to focus on quick moving objects is pretty incredible. It’s the reason that sports photographers have been willing to pay more than $6,000 for a Nikon d-4s or Canon 1dx. These cameras usually had two auto focus systems; contrast & detect, which is available on most cameras and phase detect which enabled that super quick focus on moving subjects. Face detect autofocus actually relies on a second smaller mirror reflecting some of the light down into a dedicated autofocus sensor at the bottom of the camera.
Crucially a phase detector system, tells the camera which direction to focus. Closer are farther away and it’s also pretty good at tracking foreground objects. However, it’s because the autofocus assembly is separate from the sensor a DSLR never sees what it’s focusing on. So, it can’t adapt to different scenes. Also, if the mirrors flipped up while using live view or recording the movie, the camera can’t reflect light onto that focus sensor and instead has to rely on a second system. This is the contrast-detect autofocus which analyzes the image from the sensor itself. The camera then moves folk backwards and forwards and calculates which direction yields higher contrast, which means a sharper image will keep focusing one direction until the image starts to defocus and then, reverse until it settles on the highest.
Contrast image is actually potentially more accurate than phase detect because it’s analyzing the actual image on the sensor itself but it’s much slower and it can lead to a distracting, hunting behavior where the focus wobbles in and out because they rely on contrast-detect focus. When the mirror is flipped up, most DSLRs have poor autofocus. When shooting video, it tends to be slow and the constant hunting in and out of focus can ruin shots. So, what about mirrorless cameras. Without a mirror or dedicated focus sensor, early mirrorless models were stuck with that same slow contrast detect auto focus. Around 2010 though, the first so-called hybrid autofocus systems were appearing. Starting with the Fujifilm F 300 X, are a compact point-and-shoot. These used a form of phase detect autofocus, built into the sensor itself. This quickly spread to Fuji’s higher and X line of mirrorless cameras.
A similar system was adopted by Sony for its alpha cameras in 2013. These on the sensor phase detect autofocus systems are usually slower and less accurate than the dedicated sensors in the DSLR. But, they use a really clever trick in a hybrid system, the bulk of the focusing is still done with contrast. But, it uses the phase detector system to know which direction to focus eliminating that back and forth hunting behavior.
These systems can also be used when shooting video and these days high-end mirrorless cameras can focus as well. If not, better than most DSLRs, the search and people using mirrorless and DSLR cameras for video, has actually led to an autofocus revolution because of their big sensors and inexpensive lenses starting with Canon’s 5d Mark ii. DSLRs were more and more becoming tools for video as well as photography. But, slow contrast detect autofocus meant video producers generally had to rely on manual focus. Is frustrated a lot of people and as DSLR video got popular, companies saw an opening, and developed new focus systems that worked around past limitations.
Canon actually ditched contrast focus entirely and developed a system called dual pixel autofocus, which premiered on the 70d DSLR and essentially turns every pixel into a tiny phase detect sensor. It’s now using that same system on its iOS. Panasonic created a system called depth from the focus for its gh4; a mirrorless camera that quickly became popular with video producers. Depth from D focus is a purely contrast based system and uses stored data of how various lenses distort light to know which direction to focus. This system is blazingly fast, though it only really works with Panasonic’s own lenses.
Still Panasonic claims its g9 mirrorless can use the system to lock focus; quicker than any other camera hybrid autofocus will. It really took off around 2013 though with Sony’s a7 series and it’s had an interesting side benefit. Computation based focused mode, remember DSLR phase detect systems analyze the character of incoming light but not the content. The camera can’t actually see what it’s focusing on. Sensor systems like hyper autofocus can use processing to interpret what’s actually in the scene, enabling things like eye tracking or face detect autofocus. These are potentially game-changing developments, that can greatly improve focus accuracy. After decades of cameras relying on two well-established systems, we are suddenly at a point where brands are experimenting with new and potentially, revolutionary ways to improve autofocus and mirrorless cameras are leading the way. There’s one other area we’re seeing.
Mirrorless cameras differentiate themselves from DSLRs and that’s stabilization. Mirrorless cameras are starting to make in-body stabilization the default for photography and video. Now, this is a system where the sensor actually shifts and moves to compensate for vibration, yielding sharper photos and smoother video lens based stabilization, where the individual glass elements of a lens are shifted. It has been around since Nikon introduced it in 1994. It is quite good but, it has drawbacks. Mostly, it’s expensive. You essentially pay for it with each lens you buy.