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Mirrorless Cameras: What Are They and Why Buy One?

Learn everything you need to know about mirrorless cameras, including what makes them so popular

Mirrorless cameras are the new standard in professional digital camera technology. But what does ‘mirrorless’ mean? How do they work? And why have they become the cameras of choice for the photo industry? Read on to learn all this and more.

What Is a Mirrorless Camera?

The term mirrorless camera most commonly describes a modern form of digital interchangeable-lens camera (ILC). It is called a mirrorless camera because it does not feature the reflex mirror found inside the previous iteration of digital ILC, the digital single-lens reflex (DSLR) camera.

Mirrorless cameras are now considered by many to be the current industry standard in digital photography, with growing numbers of professional photographers choosing these systems over their DSLR counterparts. This is reinforced by the fact that many DSLR product lines have now been discontinued.

What Is the Difference Between Mirrorless and DSLR?

Many factors differentiate mirrorless and DSLR cameras, including size, weight, viewfinder, and autofocus (more on these below). However, these all stem from one fundamental change: DSLRs have reflex mirrors, while mirrorless cameras do not.

What Is a Reflex Mirror?

A reflex mirror is an essential part of a DSLR camera’s optical viewfinder (OVF) system. Positioned directly behind the lens, the reflex mirror sits at a 45° angle to reflect the light that passes through the lens upwards into the camera’s OVF.

The majority of DSLRs feature a moving reflex mirror. When the shutter release is pressed, the mirror uses a spring-mounted mechanism to automatically flip out of the way, thus clearing the path for light to reach the sensor.

Once the reflex mirror is displaced, the camera’s shutter opens, exposing the imaging sensor to the same image the mirror was reflecting. This enables the photographer to see a preview of the exact composition they are framing before making a picture.

While moving reflex mirrors are most commonly found in more modern cameras, some earlier camera designs feature a fixed reflex mirror. Below, we take a closer look.

History of the Reflex Mirror

Reflex mirrors have been a feature of camera technology since its early beginnings, but they are most associated with twin-lens reflex (TLR), single-lens reflex (SLR) and DSLR cameras.

The Twin-Lens Reflex (TLR) Camera

Most popular from the 1930s to the 1950s, the TLR camera is so-called because it features not one, but two separate lenses of the same focal length on the front of the camera.

Each of these lenses has a different function: one directs light onto the photographic film to create the image; the other directs light into a viewfinder via a fixed reflex mirror so that the photographer can see what they are framing.

This allows photographers to make images immediately after achieving focus, which was a great improvement on early camera designs. In these previous designs, a focusing screen made of ground glass had to be manually replaced with a photo-sensitive plate before making an exposure.

However, while the TLR camera did speed up the process, it was not a perfect solution.

Although the two lenses are positioned very close together, there is still a degree of parallax error when framing close-ups. This means that, when the subject is viewed through the viewfinder lens, it appears in a different position to when it is viewed through the exposure lens.

In addition, the twin-lens design means TLR cameras are invariably fixed-lens, and with the viewfinder using a separate light path to the exposure, it is impossible to preview visual elements such as depth-of-field or the effects of lens filters.

The Single-Lens Reflex (SLR) Camera

A solution to these problems was the SLR camera, which uses a moving reflex mirror system.

This ability to move the reflex mirror out of the way meant it could be positioned directly in front of the film. With the viewfinder using the same light path as the exposure, photographers were able to see the exact composition their film was being exposed to before their image was made, while avoiding the arduous manual exposure process of earlier cameras.

Additionally – unlike TLR cameras – SLRs feature a roof pentaprism positioned between the reflex mirror and the viewfinder. As the light travels through this pentaprism, the inversions caused by the camera lens are corrected, so the image in the viewfinder does not appear upside down.

As designs developed, the instant-return reflex mirror was introduced. This spring-loaded system removed the need to reset the mirror before making the next photograph, achieving a fully automated exposure process.

The advantages of the viewfinder and exposure using a single lens were abundant. Aside from providing the ability to preview depth-of-field and the effect of lens filters, a major positive was that reflex cameras could now be smaller and lighter, as well as utilizing interchangeable lenses.

The Digital Single-Lens Reflex (DSLR) Camera

The advent of digital photography brought with it enormous changes to the photography industry and ushered in a whole new era of image making. The SLR camera evolved with it, most notably replacing photographic film with a digital imaging sensor – and so the DSLR was born.

While this was a major change to the inner workings of the SLR camera, the fundamental process of composing with an optical viewfinder and releasing a shutter to expose an image remained the same.

Therefore, the instant-return reflex mirror and pentaprism system continued to play a critical role inside the majority of DSLRs – and still does, even to this day.

The Mirrorless Camera

Mirrorless cameras formed the next – and current – generation of digital camera. As technology advanced, the electronic viewfinder (EVF) was introduced. This allowed the image projected onto the sensor to be reproduced on a digital screen in real time.

Such technology made the previously impossible possible: the viewfinder image and the exposed image could now follow exactly the same light path without any redirection, essentially making them one and the same.

As such, the reflex mirror that had formed such an integral part of the reflex camera design was no longer required – hence the term ‘mirrorless’.

Technically, mirrorless refers to any camera without a mirror. Therefore, any digital camera with an electronic viewfinder falls into that category, including digital compact cameras and smartphone cameras.

However, ‘mirrorless camera’ is widely regarded as a specific term to describe a digital ILC camera without a reflex mirror.

Mirrorless vs DSLR

What’s better, a mirrorless camera or a DSLR camera? It’s a question that has been fiercely debated by photographers around the world for many years. However, as time goes on and mirrorless camera technology advances, the argument is becoming increasingly one-sided.

Advantages of Mirrorless vs DSLR

The benefits of mirrorless cameras are abundant, from portability and speed to features and quality. Here are some of the best reasons to go mirrorless.

Size and Weight

Put simply, fewer parts take up less space. Therefore, without the requirement for an instant-return reflex mirror mechanism and pentaprism, it is possible for mirrorless camera bodies to be smaller and lighter than DSLRs with the same-sized sensor.

For example, the smallest and lightest APS-C mirrorless camera in FUJIFILM X Series is as slim as 32.7mm (1.29in) and weighs just 365g (0.8lb).

Electronic Viewfinder (EVF)

As outlined above, when the OVF system in SLR cameras was first introduced, its main selling point was enabling photographers to see the exact composition and depth-of-field of the image that would be projected onto the film.

The EVF takes this even further. Because the image in the viewfinder is a real-time digital representation of what the sensor sees, it is possible to preview the exact exposure and even see the effect of in-camera adjustments like contrast and color levels.

Additionally, a wide array of digital visual aids can be displayed in EVFs, such as detailed exposure settings, histograms, and various manual focusing aids.

Furthermore, the EVFs in mirrorless cameras use high-resolution digital displays, making them much more vibrant and bright enough to provide a better preview of low-light scenes than their optical counterparts.

When these factors are combined, they allow photographers not just to see how their final image will appear, but also to be much more confident in its quality – all before even pressing the shutter release.

Continuous Shutter Release

Mirrorless cameras can achieve much faster continuous shutter release speeds than DSLRs because they do not need to wait for a reflex mirror to flip up and back again each time an image is made.

Removing this extra step from the exposure process means some mirrorless cameras can achieve speeds of up to 15fps with the mechanical shutter while still tracking focus.

This is especially useful when photographing wildlife, sports, or any form of fast-moving action.

Product Development

Most DSLR product lines have now been discontinued in favor of mirrorless systems, which means the development of DSLR cameras has stopped.

Instead, mirrorless systems are now at the forefront of camera technology and enjoying the same levels of investment formerly experienced by DSLRs.

Going mirrorless is the best way to keep up with the latest in cutting-edge camera technology and design.

Advanced Video

The issue of limited product development in DSLR models has meant that mirrorless cameras are streets ahead when it comes to video features.

Even entry-level mirrorless cameras offer 4K video capabilities and professional models can achieve frame rates of up to 120p for recording super-smooth, ultra slow-motion footage.

Mirrorless cameras also benefit from better live-view autofocus performance due to their more advanced on-sensor autofocus systems (more on this below).

Early Disadvantages of Mirrorless vs DSLR

When speaking to other photographers about mirrorless cameras or researching the technology online, you may have heard or read about some disadvantages of
mirrorless systems.

These stem from the fact that, when mirrorless cameras were first introduced, the technology was relatively new and underdeveloped, especially when compared to long-established DSLRs.

However, in the years since, mirrorless camera technology has enjoyed extensive development, eliminating – and even reversing – such disparities.

Below, we offer some insight that should help debunk these negative perceptions.

Autofocus

DSLRs have historically employed a phase detection autofocus (AF) system that uses its own dedicated AF sensor.

The way this works is by using a semi-transparent reflex mirror that allows a portion of the light through to hit a sub-mirror mounted directly behind it. This sub-mirror then directs the light downwards onto the AF sensor (please refer to Figure 3 above).

Because mirrorless cameras removed the mirror system, the AF and imaging sensors had to be combined into one. In the early days of mirrorless, more primitive technology only allowed for less-efficient contrast detection AF to be used in this way – inferior to the dedicated phase detection AF sensors in DSLRs.

With critical focus essential for professional photographers, many at the time opted for the more advanced systems inside DSLRs, despite the other advantages of mirrorless.

Fast-forward to the present day and mirrorless camera technology has come a long way. Unlike those early days, the latest on-sensor AF easily rivals and often surpasses the AF systems in DSLRs.

FUJIFILM X-H2S, for example, features an intelligent hybrid AF system that combines phase detection and contrast detection to great effect.

With 425 points across the entire frame, and the ability to efficiently find focus in extremely low light, the tide has most definitely turned in terms of mirrorless vs DSLR AF performance.

Viewfinder

When EVFs were first introduced, the early technology often suffered from graininess and lag (a delay between what happened in real life and what happened on-screen). For this reason, many photographers preferred the OVFs in DSLRs, as they helped them feel more directly connected to the scene in front of the camera.

While this may have been true for early EVF technology, modern EVFs have seen vast improvements.

Some of the latest mirrorless cameras feature high-resolution, 5.76 million dot displays that create a level of clarity much closer to real life. Furthermore, advances in processor technology make lag times negligible, and EVF refresh rates of 120fps are commonplace, ensuring fast-moving subjects are easy to track.

Lens Choice

Product design and development takes time and investment, especially complicated products like camera lenses, which require extremely high levels of optical precision.

When mirrorless cameras entered the market, they were up against DSLR systems that had been built over decades. Naturally, the choice of mirrorless lenses was therefore much smaller than that of DSLRs.

However, as time has passed, early players in the mirrorless camera market have developed broad ranges of lenses for all applications that easily rival their DSLR predecessors.

For example, the FUJINON XF Lens lineup covers 35mm equivalent focal lengths that range from 12mm to 914mm, and can even be extended to 1828mm with the use of a teleconverter.

This collection includes prime, zoom, and macro lenses with apertures as low as F1. These cover all applications and genres, and even include cinema-quality optics dedicated to professional video.

Battery Life

As the name suggests, EVFs use electricity, while OVFs do not. This means mirrorless cameras consume more power than DSLRs.

When mirrorless cameras first launched, they used the same battery technology as DSLRs so, inevitably, battery life took a hit. For obvious reasons, this was a concern for photographers on the go without easy access to a power point.

However, as with all technology, batteries have seen significant developments since then. Mirrorless cameras now use the latest lithium-ion batteries, with much larger capacities that are likely to keep the average photographer creating all day.

The Future of Mirrorless Cameras

Whatever your view of mirrorless cameras, it’s safe to say they are here to stay. With many DSLR lines discontinued and mirrorless now at the forefront of digital photography, mirrorless systems are leading the charge in the advancement of camera technology.

Sensor resolution continues to rise, with 100-megapixel sensors now more accessible than ever; increasingly powerful processors are enabling the use of AI technology to drive some of the most effective subject recognition autofocus systems we’ve seen; and extremely advanced in-body image stabilization (IBIS) can now achieve an incredible seven stops of correction.

These amazing advances in technology will continue to break boundaries for photography in the future and, while we may not be able to accurately predict what’s next, one thing’s for sure: going mirrorless is the only way to experience it.

Learn more by exploring the rest of our Fundamentals of Photography series, or browse all the content on Exposure Center for education, inspiration, and insight from the world of photography.