What Is a Mirrorless Camera?

Think DSLR-like but with fewer parts

A photographer composing a sunset scene at a beach.

 @marcdb via Twenty20

A mirrorless camera, or mirrorless interchangeable lens camera (MILC), is similar to a DSLR camera, with one significant difference. The optics in a mirrorless camera do not include a reflex mirror or a pentaprism. Instead, light is fed directly to the image sensor inside the camera, where the focus of the image is determined. It's also how the photographer sees a preview of the image.

How Mirrorless Digital Cameras Work

If you know about DSLR (digital single lens reflex) cameras, then you know they have an optical viewfinder — one that you look through with your eye to frame your image. That is accomplished by having a mirror and a pentaprism inside the body of the camera. Light passes through the lens, bounces from the mirror to the pentaprism, and then through the viewfinder. 

An digital mirrorless camera with the light path labeled.

Comparing DSLR with mirrorless cameras, how does a mirrorless camera work if you remove the mirror and pentaprism? Instead of the light bouncing around to reach the viewfinder, in a mirrorless camera, it passes through the lens straight to the digital image sensor. The digital image sensor then provides a preview of the image the photographer is arranging. In some mirrorless cameras, this is through a digital viewfinder. In others, it’s through the digital LCD screen on the back of the camera. 

Benefits of a Mirrorless Camera

The functional design of a mirrorless camera offers a secondary benefit; it makes the camera much lighter. It wouldn’t seem like removing a mirror and a pentaprism would make that much difference in weight, but for photographers that are carrying a camera around all day long, it does. 

Of course, weight is one of the lesser benefits. One that’s far more important to professional photographers is the ability to use a larger variety of lenses with a mirrorless digital camera body. The lens mount on a mirrorless camera has a slightly different design, which makes it possible to add adapters (from companies like Fotodiox and Metabones) to use lenses from Sony, Canon, Fuji, and many other companies. For photographers that are heavily invested in lenses, it means you don’t have to start over with a whole new setup.

Even if you’re not a professional photographer, mirrorless cameras could be beneficial. You want to have a camera that will take create pictures in a variety of situations, and having an interchangeable lens camera is a good option for that. Mirrorless cameras offer not only a lightweight solution, but some also have great digital image sensors. For example, the Fuji GFX 50s has a medium format sensor (which is larger than a 35 mm full frame but smaller than a large format sensor). This is important because the image sensor is what you rely on to ensure you’re taking great photos.

Downfalls of Mirrorless Cameras

Mirrorless cameras are great in some aspects, but in others, they don’t perform as well as DSL cameras. For example, because a mirrorless camera relies heavily on the digital image sensor, it has a much shorter battery life than a DSLR camera. 

If you take a lot of photographs in low-light conditions, the autofocus on a mirrorless camera could also prove to be problematic. That’s because most mirrorless cameras use contrast to focus. The camera finds the darkest spot in an image, and uses that as the main focal point. In low-light situations, enough light may not travel through the lens to the image sensor to get a clear, sharp image.

What Does a Mirrorless Camera Cost?

If you’re hoping to cut costs by buying a mirrorless digital camera, you’re may be disappointed. Interchangeable lens digital cameras can cost as much as DSLR cameras. However, if you’re not convinced that you need interchangeable lenses, a mirrorless digital bridge camera could be a better choice. You’ll have some of the flexibility of a DSLR without the interchangeable lenses, but most bridge cameras offer a versatile, fixed lens that fits the needs of many casual photographers. And you can usually find one on the lower side of the price scale.