Digital cameras today tend to fall under one of two categories: SLR or mirrorless.
It turns out that many of the changes to how cameras work have been attempts to solve a simple problem: How do you show what’s in front of the lens to both the user and whatever’s recording that image?
From glass plates to mirrors
Originally, photographs weren’t on film; instead, you’d coat a metal or glass plate with a photosensitive liquid. This would be placed behind the lens — before you did so, however, you looked through where the plate would later be to frame the photo.
To speed up the process, a second lens was added near the first, through which framing and focus could be adjusted without fiddling with the primary one.
Although these offset lenses only offered an approximation of what the primary lens would see, the design persists to this day. They’re called “rangefinder” cameras, and the lens you look through has been given additional functionality, notably the ability to determine the distance to the subject for the purpose of setting focus.
Mirrors were added around the turn of the century (the last one, to be clear), allowing for two new camera types. One was a “twin-lens” setup where the mirror bounced the image from the extra lens upwards onto a small translucent screen; a second, similar lens just below opened onto the shutter and the film itself, and focusing the first would also focus the second.
From mirrors to LCDs
In a way, mirrorless cameras are very much like the familiar point-and-shoot cameras, in which the lens sits directly in front of the shutter and film or sensor. This solves the problem of how to get the view from the lens to both the user’s eye and the image capture mechanism: the image hits the sensor, which then relays that image to the LCD facing the user.
The primary advantage of mirrorless camera systems is their compact size. Because they require few or no moving parts inside (some retain a mechanical shutter, for instance), they can be thinner and lighter, or add other functions, like in-camera image stabilization. There’s also a motivation to use high-quality displays and intuitive touch controls, since they will be relied upon more than in SLRs.
After all, when you are seeing the light as it comes through the lens itself, there is no lag or color bias.
Mirrorless cameras have helped invigorate a flagging photography market long divided into “cheap” and “serious.” Compact, powerful, and intuitive, the mirrorless camera is in many ways the best of both worlds.