What is a Mirrorless Camera?

February 24, 2020

We’re sure by now you’ve heard the term ‘mirrorless’. You may have wondered why cameras need or don’t need mirrors at all. Whatever your knowledge is on the topic, don’t worry—we’ll break these things down for you very simply.

If you’re in the market for a new camera, it’s great to be aware of what your options are. Different cameras will suit different photographers. Mirrorless cameras are just one of these choices, and knowing what you need from your future camera is a great place to start. We’ll explain what they are and how they compare with DSLRs (Digital Single Lens Reflex Cameras). 

Mirrorless cameras go by several other names, but there is one you won’t forget: EVIL. But don’t be afraid! If the term mirrorless wasn’t clear enough, this acronym says it all. It merely stands for Electronic Viewfinder, Interchangeable Lens. What distinguishes these cameras from DSLRs is the first component of the acronym, the EV or EVF (electronic viewfinder). The second component, interchangeable lens, is what they share in common with DSLRs. But if you’re still wondering why mirrors are important to DSLRs, let’s dive in.

Mirrorless? What is their role in DSLRs, first of all?

DSLR cameras need mirrors; they have two main ones, and both are fundamental to this type of camera. The first mirror catches light from the lens at a 45° angle. When a photo is taken, this mirror flaps upward and enables light to hit the image sensor behind it. And the ‘click’ or ‘shutter’ you hear is this mirror getting out the way of the image sensor. Generally speaking, shutter speed is limited in a DSLR by how quickly this mirror can move. It also results in the viewfinder darkening momentarily. Why? Let us introduce the second mirror.

The second mirror is fancier. This is known as the pentamirror or pentaprism (depending on the build quality). But let’s not get technical. When a photo is not being taken, this prism directs light, upright, to the viewfinder for framing. Older cameras from the analogue era depended on users looking down onto the first mirror we discussed before. Those cameras lacked any pentaprism, but prompted their invention.

When a shot is taken the viewfinder goes black because the first mirror ‘clicks’ upward and blocks light from entering the pentaprism (and the viewfinder); it hits the image sensor instead, and the image is recorded. The mirror resets to its 45° angle and the viewfinder is clear again.

Both of these mirrors add weight and bulk to the DSLR camera body. Moreover, the pentaprism only provides 100% accurate image representation in the highest tier of models. They are typically about 96% accurate.

How could a camera be mirrorless, then?

We hinted at this already. It’s part of our little acronym. The image preview is given on a small screen which replaces the optical viewfinder. It is an electronic viewfinder, the EV, or the EVF. Natural light from the scene is replaced by a digital representation from the image sensor. By having the image sensor and the viewfinder communicate electronically, the need for mirrors and prisms is nullified. 


What are the pros and cons?

Compared to DSLRs, mirrorless cameras have several strengths. Naturally, they have a few weak points and many similarities, too. It should be noted that mirrorless cameras are not objectively better than DSLRs, it isn’t that simple. Consider these notes in combination with your own needs as a photographer.

The strengths

  • Generally speaking, mirrorless cameras are lighter and more compact than their self-reflecting cousins. This is the result of a shorter ‘flange’ distance without mirrors—the length between the lens and the image sensor—that results. The exception is this: some mirrorless cameras are designed larger for a bigger battery and EVF system.
  • Fewer moving parts allows for quiet, even silent, camera shutter. It also enables very fast shutter speeds with less mirror shock and blur. 
  • Sophisticated electronic viewfinder. On all EVFs exposure can be previewed in real- time, and always with 100% framing accuracy (unlike DSLRs). Not only is exposure shown, but also depth-of-field, white balance, colour balance and more. For precise manual focus it is also possible to view a portion of the frame up close in many mirrorless cameras.
  • Improved visibility through the EVF in low light conditions. While screen flicker and noise can occur, the ability to boost the exposure preview in low-light makes for easier shooting overall. 
  • No lag delay during continuous/burst shooting modes.
  • High quality video recording capability. It is not uncommon for mirrorless options to provide video support for 1080p and 4K resolution. Images can be taken during recording as well.
  • With adapters, legacy lenses (your old SLR and rangefinder camera glass) can be used on mirrorless cameras. This is also possible using current lenses of other brands, easily and immediately increasing the range of lenses at one’s disposal. 
  • Mirrorless cameras like the Olympus OM-D EM-10 Mark II and the Sony A7R Mark II offer 5-axis image stabilisation, something just not found in the DSLR market.


  • While they have steadily improved, the limited resolution of the EVF takes some getting used to. This change is most apparent if you move from DSLRs to a mirrorless, but less so if it’s your first camera beyond a smartphone. Having said that, the resolution of EVFs has progressed remarkably in recent years. The EVFs have become brilliant in many within the current range.
  • Even if mirrorless camera bodies are small and compact, the same reductions in size can hardly be made to their lenses. This applies mainly to mirrorless cameras with full frame image sensors. It is not the case for those that are smaller; the bigger the image sensor, the greater the difference between body and lens. A large lens tacked on the end of a full frame mirrorless camera may feel imbalanced. Battery grips are a quick fix here, but a fix nonetheless.
  • Mirrorless cameras are less ergonomic in the hands. While this is not the case for every model, and while their thin, compact form is somewhat beneficial (attractive, portable, easy to pack, etc.), their shallow grip may leave some users feeling insecure without a camera strap.
  • Most mirrorless cameras still use contrast-detection AF, meaning they focus in and out searching for, naturally, the highest contrast edges within the frame. This is opposed to superior phase-detection AF, which is more common and easier to achieve in DSLRs (with another mirror). This has been overcome by some using both AF kinds. They are called hybrid mirrorless cameras.
  • If you are looking for a professional level mirrorless camera, they aren’t more affordable than DSLR options and with fewer lens options, however this is changing rapidly. Consider the price of lens adapters when determining this. 
  • Mirrorless cameras drain batteries fast. They depend on running the EVF and/or LCD at all times, meaning their image count rarely exceeds 400. The Canon EOS RP handles just 250. The Sony A7R III—650 shots. But spare batteries aren’t a major hindrance; battery grips are also available, but while these tend to supplement DSLR cameras, you mightn’t ever take it off your mirrorless camera.

The similarities

Both cameras are available with full frame image sensors and APS-C, ‘crop sensor’ options. In fact, many of these cameras contain the same image sensors. They are both capable of producing high quality images. 

As mirrorless cameras expand their lens and accessory ranges, the choice will simply become a user’s preference. Just as analogue cameras are used and appreciated by many, there is no reason DSLR cameras will be replaced by mirrorless ones.

Both camera styles tend toward durable, weather sealed bodies. Alloy bodies may add a little weight to these cameras but they remain in proportion to one another. 


Mirrorless cameras depend less on optics. They use electronic viewfinders (except certain, newer DSLRs) and share their ability to change lenses with DSLR cameras (with a few less lenses to choose from). If you are a beginner, you will benefit from using a mirrorless camera with its sophisticated image preview, particularly as an aid to learn manual mode. There are plenty of portable options and plenty of attractive ones, too (but these factors vary between brands). However, from a price point, you may benefit more from entry level DSLRs like the Nikon D3500, capable of shooting 1,550 shots in a single charge. 

If you are a professional, ask yourself what you will gain from using a mirrorless camera. If video is important to you, or you’re after something faster, lighter—these cameras will serve you very well. 

Mirrorless cameras may feel like a natural improvement from DSLRs. This is not the case. While they may be experiencing faster growth at this time, this does not in anyway reflect the preferences of photographers using them. They are simply another option. Arguably the most divisive factor is the electronic viewfinder. What do you prefer, optical or electronic?

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