DSLRs have certain limitations when compared to mirrorless cameras. It is partly due to the fact that SLR cameras were originally designed for film. Digital was initially treated the same as film and housed in the exact same mechanical bodies. Except for the new circuitry and electronics required to create digital film media and the back LCD, all other components remained the same. The same mechanical mirror, same pentaprism/optical viewfinder, same phase-detection mechanism for autofocus operation.

Although technological advancements eventually allowed for the expansion of camera features (in-camera editing and HDR, GPS and WiFi), DSLRs remained bulky for a few reasons. The mirror in DSLR cameras was required to be exactly the same size as the digital sensor. This took up a lot of space. The pentaprism had to be the same size as the mirror. This made the DSLR’s top bulky. Manufacturers wanted existing lenses to be compatible with digital cameras so that consumers could switch from film to digital without too much hassle.

Manufacturers had to maintain the same “flange distance” between the formats. This means that the distance between the camera mount (and the film/sensor plane) must be maintained. While smaller APS-C / DX lenses and sensors seemed to be a great way of reducing the size and weight of DSLR systems, their compatibility and flange distances made them heavy and bulky physically. Modern full-frame digital cameras brought 35mm back, and mirror and pentaprism sizes returned to film size. The flange distance between the lenses was kept the same to ensure maximum compatibility with full-frame DSLRs and film cameras. However, DSLRs cannot go beyond the minimum size requirements. The presence of the mirror makes them more difficult to support and build.

DSLR Camera Limitations

They are limited by the mirror dependence of DSLRs that allow for “through-the lens” (TTL), viewing.

  1. Size and bulk: The reflex system requires space for the mirror and prism. This means that DSLRs will always feature a larger camera body and a protruding roof. This means that the viewfinder must always be in the same place on all DSLRs, aligned with the digital sensor and optical axis. Most DSLRs share a similar exterior design.
  2. Weight Larger sizes and heavier weights also translate to more weight. Although entry-level DSLRs are made of plastic and have internal components that make them lighter, there is still a minimum height and depth requirement to hold the mirror and pentaprism/ pentamirror. This means that there is a lot of space wasted.
  3. Complex Shutter and Mirror Design Every actuation requires that the mirror move up and down in order to allow light to pass directly onto the sensor. This alone can lead to a variety of problems.
    • Mirror Slap DSLR cameras make a lot of noise due to the shutter mechanism moving up and down every time an image is taken. Camera shake is also a result of this mirror slap. Although manufacturers have come up with innovative ways to reduce noise (Nikon’s Quiet mode, for instance), it can still be heard. When shooting at long focal lengths or slow shutter speeds, camera shake can be a problem. DSLR manufacturers needed to create features such as “Mirror Lock Up” and “Exposure Delay” in order to lift the mirror, then expose after a predetermined delay. This was done to reduce vibrations from mirrors.
    • Frame Speed Limitation – While modern mirrors and shutter mechanisms look amazing, their speed is limited by how fast the mirror flips up or down. The mirror flips up and down eleven times per second when the Nikon D4 fires 11 frames per second. The shutter opens and closes in the middle. To make it work, both the shutter and the mirror must be in perfect sync.
  • Imagine this happening at 15-20 times per second. It’s almost impossible.
  • Costly to Build and Maintain The mirror mechanism is complex and has many parts. It is therefore very expensive to build and offer technical support in the event of a problem. A service center can take a lot of time disassembling a DSLR or replacing its internal components.

Advantages of Mirrorless Cameras

Many manufacturers are realizing that traditional DSLR systems will not be the main driver of future camera sales with the advent of mirrorless cameras (hence “mirrorless”) This makes sense economically, but when we look at current innovation, where is DSLRs at? Each iteration of DSLRs seems to be closer to the point of no return. Autofocus accuracy and performance have almost reached the limit. The processors can run a lot of FPS and produce 4K video at high resolution. Camera manufacturers are rebranding their cameras under new models to maintain sales and keep word of mouth going. What other features are there? More in-camera editing options? Different types of photography require specific features? These are great features, but will they really drive future sales? I don’t believe so.

Mirrorless cameras offer huge potential for innovation and address many of the issues that traditional DSLRs face. Let’s look at each point and talk about additional benefits of mirrorless camera:

  1. Less bulk and lighter: By removing the pentaprism and mirror, you can free up lots of space. Mirrorless cameras are smaller than DSLRs and can therefore be lighter, more compact and less bulky. The physical size of the lens and the camera is decreased by having a shorter flange distance. This is especially true with APS-C-sized sensors. Full-frame sensors are more difficult to deal with, as we will discuss later in this article. There is no more waste space and there is no need to add ruggedness to make it feel larger. Mirrorless cameras are noticeably lighter than DSLRs. Smartphones as compact cameras have taught us an important lesson: convenience, small size, and light weight can sometimes overpower quality. Point and shoot sales are virtually dead because most people consider their smartphones “good enough” to capture those moments. Smartphone manufacturers are focusing on camera features because they want consumers to believe that they get more than a smartphone. It is evident that it is working, judging by the sales figures. More people are switching to smartphones and leaving behind their old compact cameras. In today’s economy, electronics that are smaller and lighter in weight win. The same trend can be seen in other gadgets such as thinner TVs and lighter laptops, tablets, etc. People will naturally gravitate to smaller and lighter gadgets, particularly if they are not compromised in quality.
  2. No Mirror Mechanism No more mirror flipping up or down. There are many good things.
    • Less noise: No more mirror slaps, the shutter mechanism clicks and that’s all you hear from your camera.
    • Less Camera Shake The camera shutter is the only component of a mirrorless camera that can produce vibrations. Even then, electronic front curtain shutters (EFCS) can be used to disable shutter and allow for electronic shutter to eliminate shutter shake.
    • Cleaning is much easier than cleaning DSLRs. Most cameras don’t require a fully charged battery in order to lock the mirror. The sensor can be exposed after you have removed the lens. Some cameras with in-body imaging stabilization should have the stabilization mechanism locked via the camera menu to avoid movement or damage. A majority of mirrorless cameras don’t have an opening underneath the mirror for a phase detector sensor or other components. This means that dust can not circulate once the chamber and sensor have been cleaned thoroughly.
    • Potentially Very High FPS Speed: Having no mirror means that the capture speed (FPS), does not need to be restricted by the mirror speed. Mirrorless cameras can capture images at frame rates up to 10-12 FPS, which is much faster than the current 10-12 FPS.
    • Less expensive to build and maintain. This is because there are fewer moving parts, which means lower manufacturing costs and better support for the manufacturer.
  3. Live Preview (WYSIWYG ) : With mirrorless, you have a preview of the image you are about to capture. Basically “What you see is what it gets” (WYSIWYG). Live preview will show you what you did wrong with White Balance, Saturation, or Contrast. This can be done in either the LCD (see below), or in the EVF.
  4. No phase detection / secondary mirror alignment issues. Many modern mirrorless cameras now ship with hybrid autofocus systems which use both phase and contrast detection autofocus. The phase detection sensors on a variety of mirrorless cameras are now located on the actual sensor. This means that the phase detection sensor will not need to calibrate for distance because it is on the same plane that the sensor that captured the image.
  5. Price: Producing mirrorless cameras can be cheaper than making DSLRs. Mirrorless camera manufacturers are charging high premiums for their systems today because of their high overall costs and limited production. Although manufacturing costs are less than DSLRs, companies still have to invest a lot of R&D money in order to improve certain camera features, such as autofocus performance or other technologies, like EVF. Mirrorless cameras will become more affordable over time.
  6. Electronic Viewfinder Here’s the greatest strength of mirrorless cameras, and the future + present innovation that goes with it. An EVF offers a lot more advantages than OVF. Although the current EVF implementation is not as robust or responsive as it should, manufacturers will soon fix it. Let’s look at some of the main benefits of EVF over other forms of fertility.
    • Information overlay: With OVF, you can only see basic grids. Some static information is displayed in the viewfinder. However, it cannot be changed or removed. EVF allows you to view any information that you need, from live exposure data to histograms. You can add warnings, such as one for a blurry shot.
    • Live Preview The same preview can be seen inside the EVF.
    • Image Review is another important feature you won’t find in an OVF. It allows you to review images. It is amazing to be able to view the image you just captured right in the viewfinder. OVF forces you to see the LCD screen in bright light, which can be a pain. To see the LCD screen in daylight, many people buy specialized loupes. EVF eliminates this concern as you can instead use the viewfinder to review images.
    • Focus Peaking is a useful tool that lets you see which areas of the frame have been centered. You can focus manually without having to rely on the eyes. You can paint the area in focus with any overlay color you choose, and it will stop exactly where you want. This is impossible with an OVF on a DSLR.
    • Viewfinder Coverage Issues – OVF typically provides 95% or more viewfinder coverage on low-end DSLR models. This means that the viewfinder will show you a smaller amount of what the camera will record than what you see. EVF eliminates this problem. The EVF will provide 100% coverage.
    • Brighter Display: If the lighting conditions are dim, an OVF will not allow you to see as well. Low light can make it difficult to focus with OVF because you cannot tell if the subject has been in focus until you take a picture. EVF can “normalize” brightness levels so you can see everything like it is daylight. Although some noise may be present, it is better than trying guess through an OVF.
    • Digital Zoom – This is my favorite feature! You’ve probably used Live View on your DSLR before and know how useful zooming in on a subject is. Modern DSLRs can zoom in up to 100% and get a great focus. This feature is possible with mirrorless cameras! Imagine manually focusing with the lens and zooming in at 100% inside the viewfinder, before taking a photo. This is possible with virtually every mirrorless camera. An OVF wouldn’t be capable of zooming like this.
    • Eye Tracking – Now we move to the best part of EVF technology. The EVF displays what happens on the sensor and allows for additional data analysis to be used to do amazing things like eye-tracking or face recognition. You may have already seen face tracking with smartphones or point-and-shoot cameras. But, if you go one step further, the camera could automatically focus on the eye nearest to the subject you are photographing. This is so cool! This is a common practice among many camera manufacturers for their mirrorless cameras.
    • Potentially Unlimited focus Points: Most DSLR cameras only have a few focus points. They are mostly located in the middle of the frame. It works in most cases, but what if the focus point needs to be moved to the border of the frame? You have two options: focus and recompose. However, this might not always be a good idea as you will also need to shift the focus plane. Focus hunting is a problem that the camera may experience if it moves away from the central focus point. This limitation can be lifted with mirrorless cameras and phase detection sensors directly placed on the imaging sensor. Contrast detection has been possible on any imaging sensor. However, most mirrorless cameras now have the ability to focus using on-sensor phase detector. Focus points are distributed across the entire sensor from the extreme borders to the majority.
    • Subject tracking and other future data analysis: If you think that mirrorless cameras can do things like eye and face tracking, then imagine what the future holds for camera manufacturers. Imagine a sophisticated tracking system that intelligently blends sensor data with autofocus to track an object or subject within a frame. This is something already possible with many mirrorless cameras. Full subject tracking is a challenge for even the most expensive DSLR cameras. Tracking birds in flight can be difficult if the bird moves outside of the focal point area or the lighting conditions are not ideal. Mirrorless cameras can be very sophisticated and advanced if data is analyzed at the pixel level and there is no autofocus area.
    • Eye Injury: When looking through a viewfinder one must be careful not to photograph bright sources of light, such as the sun, especially with long focal length lenses. EVF projects the image through the sensor, so there are no eye injuries.

Limitations of Mirrorless Cameras

We have already discussed the many benefits of mirrorless cameras over DSLRs. Let’s now discuss some of the limitations.

  1. EVFlag: Some EVF implementations currently in use are not responsive and can cause significant lag. This is definitely a problem compared to OVF, but it will be fixed in the near future. EVFs have improved significantly in recent years. The lag issue with EVF technology will eventually be solved.
  2. Continuous Autofocus/Subject Tracking. While contrast detection is impressive on mirrorless cameras they still struggle with continuous autofocus performance, subject tracking and phase detection AF. We have seen incredible continuous autofocus capabilities in mirrorless cameras thanks to the continuous development of hybrid autofocus systems (where both phase detection and contrast are combined), and we already have them. Mirrorless cameras will soon surpass DSLR cameras in terms of AF performance.
  3. Battery life is another drawback of mirrorless cameras currently. Mirrorless cameras can only take 300 shots per charge because they are constantly providing power to EVF and LCD. DSLRs, on the other hand, are more efficient with a typical 800+ shot range per battery charge. It isn’t a problem for most camera users, but it can be a problem for those who travel and have limited power. The battery issue will be addressed in the future, and we already have much better battery life with the third generation of Sony A7-series camera models. The batteries will become more powerful and more power-hungry LCD/EVF screens will be replaced by more efficient technology.
  4. Red Dot patterns: Due to their very short flange distances, many mirrorless cameras have a “red dots pattern” problem. This is evident when the sun is in the frame and the aperture is small. The idea is that light rays bounce back-and-forth between the sensor’s rear lens element and the sensor, creating grid patterns in images of red (and other colors). This limitation is applicable to all mirrorless cameras that have a very short flange distance.
  5. Strong EVF Contrast Many EVFs today have a strong contrast. This is similar to what you see on your TV. You will see lots of blacks and whites but very few shades of gray. Although it’s possible to see the overlay of histograms in EVF, it can still be annoying. Manufacturers will need to come up with ways to make EVFs show images more naturally.

The list is quite short, and I believe it will get shorter over the next few years. All of these issues can be addressed and will improve with every iteration.

Summary: I believe that DSLRs will never be able to compete with mirrorless cameras in the future. While I don’t expect everyone to switch to mirrorless cameras any time soon, I do believe that many will. It is not logical for manufacturers to invest in DSLRs that are better than mirrorless cameras when the technology advantage is clear.

Buying Into a “System”

The sales data for the past few years is quite confusing. If mirrorless is the future of photography, then why does the market still favor DSLRs? There are several reasons, according to me. It takes time to convince potential buyers that “newer and better are not always better”. It is still relatively new to use the term “mirrorless”, so it takes time to educate people about its benefits. People are resistant to switching systems because of their existing investments. One can avoid the hassle of selling all their lenses and accessories if they already have a lot of them.

It can be expensive in terms of gear expenses (especially cameras and accessories), and the time required to adapt and learn new tools. Last but not least, before they make the decision to move, many photographers evaluate the entire camera system and consider the pros and cons of each system. Mirrorless systems are still in their infancy and may only have a limited number of lenses. This is true for accessories that may be available for DSLRs but not for mirrorless cameras.

But things are changing quickly. While mirrorless systems used to have a limited number of lenses, the list of lenses available today is vastly expanded and covers many photographic needs. Tilt/shift and super-telephotos are the most difficult to fill, but this will change as mirrorless becomes more advanced in autofocus.

Comparison of Mirrorless and DSLR AF Performance

Mirrorless cameras are rapidly changing, and one can laugh about how terrible autofocus was on older mirrorless cameras. Many mirrorless cameras have outperformed DSLRs in AF performance, accuracy, and quality for portrait photography thanks to features like eye-tracking. Mirrorless cameras like the Sony A9 have shown that they can compete with DSLRs when it comes to fast action shooting. We will soon see complex AF implementations that DSLRs cannot match. Some cameras can record images before and after the shutter is opened. This allows subjects to see clearly and avoids taking photos of them with their eyes closed. We have seen cameras take pictures as soon as the subject smiles. Cameras cannot display such advanced intelligence until the light continuously reaches an imaging sensor. Advanced analysis of the scene makes it easier to track subjects. The camera can also predict movement and direction.

Future Innovation

In terms of technological advances, DSLRs are not as innovative as mirrorless cameras. While we can get better resolution and video features and may have more features such as WiFi and GPS, it is not enough to excite younger photographers. There will be many new features in mirrorless cameras, as the possibilities are endless. EVFs and autofocus can do a lot, just by using advanced display technologies and analysis of on-sensor data.

Conclusion – Are we there yet?

Mirrorless mirrorless technology is moving at a rapid pace, but there are still some issues to be resolved. Mirrorless cameras can make improvements in several areas: better battery life, reliable autofocus systems, larger buffers, better lens choices (especially tilt-shift and super telephoto lenses), and improved EVFs. Although the gaps remain, they are closing quickly. In the coming years, mirrorless options for modern DSLRs will be offered by camera manufacturers.