What’s the Difference and Limitations Between DSLR and Mirrorless Cameras

DSLR vs. Mirrorless Cameras: Which Is Better for You?

For the most part, DSLRs use the same design as the 35mm film cameras of days gone by. A mirror inside the camera body reflects light coming in through the lens up to a prism (or additional mirrors) and into the viewfinder so you can preview your shot. When you press the shutter button, the mirror flips up, the shutter opens and the light hits the image sensor, which captures the final image. We’ll go through the features and capabilities with our top DSLR pick, the Nikon D3400.

In a mirrorless camera, light passes through the lens and right onto the image sensor, which captures a preview of the image to display on the rear screen. Some models also offer a second screen inside an electronic viewfinder (EVF) that you can put your eye to. Our example of a mirrorless camera, one of our favorites, is Sony’s A6300.

What is a DSLR Camera?

DSLRs use the same design as the 35mm film cameras from the past. A mirror inside the camera body reflects the light coming in through the lens up to a prism, and into the viewfinder for you to preview your shot. When you press the shutter button, the mirror flips up, a shutter opens and the light falls onto the image sensor, which captures the final image.

Here’s how the two technologies compare.

Benefits of mirrorless cameras

These new types of cameras offer some significant benefits over traditional DSLRs, but come with some important limitations as well. Remember, we’re not here to discuss which one is better – that’s something that only you can answer, given your unique needs as a photographer. It is important to know that mirrorless cameras do have some notable selling points, but also some drawbacks as well.

Sensor size

Another component of mirrorless cameras that is a bit more technical in nature, but just as important to understand, is that of sensor size. In digital cameras the image sensor is essentially a piece of digital film that captures light, in much the same way actual film does. Full-frame DSLR cameras have image sensors that are the same size as a piece of 35mm film, but most consumer-grade DSLRs, and virtually all mirrorless models, are crop-sensor cameras.

Focus peaking and sound

There are other benefits to mirrorless cameras as well such as focus peaking (the ability to see, when focusing manually, the exact pixels on your image that are in focus), quieter operation due to the lack of a flip-up mirror, and fewer overall moving parts which means a longer theoretical lifespan. But in order to get an accurate view of the situation, let’s take a look at some of the disadvantages as well.

Drawbacks of mirroless cameras

Things are looking quite promising over in Mirrorless Land, but it’s not all sunshine and roses just yet. There are some notable drawbacks to this technology, and if you don’t look at all the details you might end up with a camera that is ill-suited to your needs as a photographer.

Battery life

Currently, one of the most important limitations is battery life: they simply do not last long. The only time a conventional DSLR consumes power when not in Live View mode is when you actively measure the scene or write image data to the memory card. If you hold the camera and look through the viewfinder, no power is consumed. Therefore, it is common to achieve a thousand pictures or more with a single battery charge. Power usage is a bit different on mirrorless cameras for two reasons. First, batteries are smaller because the cameras themselves are smaller, and second they essentially operate in live view mode 100% of the time. Mirrorless cameras generally get a couple hundred shots on a single battery charge, which is nothing to sneeze at, but nonetheless a significant difference between them and their old-school brethren.

More accurate image preview in the viewfinder

Another benefit that mirrorless cameras enjoy over DSLRs, is a viewfinder that displays a more accurate representation of what your final photograph will look like. If you look through the viewfinder of your DSLR and adjust settings like ISO, aperture, and shutter speed, you might notice that the image in the viewfinder doesn’t change. It’s not until you actually take a photograph that you see what effect your alterations had on the photograph. At that point you can look at the picture on the rear screen and judge whether you need to change things for subsequent pictures. Because mirrorless cameras use electronic viewfinders, you can see in realtime the effect that things like aperture and ISO adjustments will have on your pictures before you press the shutter. This can have a dramatic effect on how you shoot, as it removes some of the guesswork with your camera settings.

Size

Perhaps the most significant difference between mirrorless and traditional DSLRs is their size: because the flip-up mirror mechanism, combined with the light-reflecting prism, are no longer needed these cameras are typically much smaller in size and weigh less too. This can be important if you are someone who likes to take your camera with you wherever you go, especially if the weight of your DSLR starts to drag you down after a day of shooting. It also means the lenses are smaller too, so you can fit several in your camera bag whereas before you might have only had room for one or two.

Bottom Line

Mirrorless cameras have the advantage of usually being lighter, more compact, faster and better for video; but that comes at the cost of access to fewer lenses and accessories. DSLRs have the advantage in lens selection and an optical viewfinder that works better in low light, but they are more complex and bulkier. Today’s mirrorless and DSLR cameras both display just how far digital camera technology has come, as both carry the ability to produce outstanding image quality with stunning performance and convenience.

Focusing system

Another limitation that is worth mentioning is the focusing system. Most mirrorless cameras use a technology called contrast detection, which is simply not as fast as the traditional phase-detection method used in DSLRs. While the former gives you access to a wider area of the frame in which to focus, it simply cannot match the speed of the latter which limits the appeal of mirrorless camera for things like sports and fast-moving wildlife photography. Some manufacturers are starting to utilize phase detection in their mirrorless models, as well as hybrid systems that offer the best of both worlds, but for now it’s safe to say that standard DSLRs are generally better suited for sports, wildlife, and other types of action photography.

DSLR Camera Limitations

Due to the mirror dependency of DSLRs for “through the lens” (TTL) viewing, they have the following limitations:

Size and Bulk: the reflex system needs space for both the mirror and the prism, which means that DSLRs will always have a wider camera body and a protruding top. It also means that the viewfinder must be fixed in the same spot on every DSLR, in-line with the optical axis and digital sensor – basically, there is no other place to put it. As a result, most DSLRs have somewhat similar exterior looks.

Weight: large size and bulk also translates to more weight. While most entry-level DSLRs have plastic bodies and internal components to make them lighter, the minimum height and depth issue to house the mirror + pentaprism / pentamirror means lots of wasted space that needs to be covered.

Complex Mirror and Shutter Design: every actuation requires the mirror to move up and down to let the light pass through directly onto the sensor. This alone creates a number of issues:

Mirror Slap: the most amount of noise you hear on SLR cameras comes from the mirror slapping up and down (the shutter is much quieter in comparison). This mirror slap results in loud noise and camera shake.

Movement of Air: as the mirror flips up and down, it moves plenty of air inside the camera chamber. And with air, it also moves dust and other debris around, which eventually ends up on the camera sensor. Some people argue that their DSLR cameras are better suited for changing lenses than mirrorless cameras, because there is a mirror between the sensor and the mount.

Frame Speed Limitation: while the modern mirror and shutter mechanisms are very impressive, they are limited by the physical speed at which the mirror flips up and down.

Expensive to Build and Support: the mirror mechanism is very complex and consists of dozens of different parts. Because of that, it is expensive to build and provide technical support if anything goes wrong. Disassembling a DSLR and replacing internal components can be very time consuming.

No Live Preview: when looking through an optical viewfinder, it is impossible to see what the image is actually going to look like. You have to look at the camera meter (which can be fooled in some situations) and adjust the exposure accordingly.

Secondary Mirror and Phase Detection Accuracy: you might already know that all DSLR cameras with phase detection autofocus system (more on this below) require a secondary mirror.

Phase Detection and Lens Calibration Issues: the problem with the traditional DSLR phase detection system not only lies with the secondary mirror alignment issues, but also requires lenses to be properly calibrated.

Price: although manufacturers have gotten much more efficient over the years in terms of DSLR production, assembling the mirror mechanism is no easy task. Lots of moving components mean high precision assembly systems, the need for lubrication in areas where metal components rub against each other, etc. In turn, this all results in increased manufacturing costs (although DSLR manufacturers have gotten very efficient in this regard). And it does not stop there – if anything goes wrong with the mirror mechanism, the manufacturer must repair or even potentially replace it, which is a very labor-intensive task.

Mirrorless Camera Limitations

We’ve gone over the many advantages of mirrorless cameras over DSLRs. Now let’s talk about some of their current limitations:

EVF Lag: some of the current EVF implementations are not very responsive, resulting in considerable lag. While this is certainly a nuisance compared to OVF at the moment, it is a matter of time before that lag is eliminated. The latest EVFs are already much better than what they used to be before. But as EVF technologies evolve, the lag issue will be resolved completely.

Continuous Autofocus / Subject Tracking: while contrast detect has already reached very impressive levels on mirrorless cameras, they are still very weak at continuous autofocus performance and subject tracking. This makes them pretty much unusable for wildlife and sports photography at the moment. However, with the rise of hybrid autofocus systems and their continuous development, we will soon start seeing mirrorless cameras with much better continuous autofocus capabilities. One of the reasons why mirrorless cameras have been slow in this department, is because most mirrorless systems are small and not well-suited to handle large telephoto lenses. So manufacturers have not been putting much of their R&D efforts into this specific area. Again, it is a matter of time until this is implemented on mirrorless cameras.

Battery Life: another big disadvantage of mirrorless cameras at the moment. Providing power to LCD and EVF continuously takes a toll on the battery life, which is why most mirrorless cameras are rated at about 300 shots per battery charge. DSLRs are much more power efficient in comparison, typically in 800+ shot range per charge. While it is not a huge problem for typical camera use, it could be an issue for someone that travels and has very little access to power. Still, I believe that the battery issue is also something that will significantly improve in the future. Batteries will be more powerful and power-hungry LCD screens will be replaced with OLED and other much more efficient technologies.

Red Dot Patterns: due to the very short flange distance, most mirrorless cameras suffer from a “red dot pattern” issue, which becomes clearly visible when shot with the sun in the frame at small apertures. Basically, light rays bounce back and forth between the sensor and the rear lens element, creating grid patterns of red (and sometimes other colors) in images. Unfortunately, there is no way around this limitation on all mirrorless cameras with a short flange distance, as discussed here.

Strong EVF Contrast: many EVFs designed today have very strong, “boosted” contrast, similar to what we see on our TVs. As a result, you see a lot of blacks and whites, but very little gray shades (which help to understand how much dynamic range can be captured). While one could look at the histogram overlay in EVF, it is still a nuisance. Manufacturers will have to find ways to make EVFs display images more naturally.

Mirrorless vs DSLR AF Performance

Speaking of which, if a couple of years back one could laugh at how bad autofocus was on mirrorless cameras, things are changing rapidly today, in favor of mirrorless. Unless DSLR manufacturers find ways to convert optical analog output into digital for further analysis, mirrorless will soon surpass DSLRs in AF performance and especially AF accuracy. How? It is quite simple: data derived directly from the recording medium (camera sensor) cannot be analyzed on a DSLR, because that path is blocked by the mirror and the closed shutter in front of the sensor. Autofocus is performed via the AF module, which receives light / analog image from the secondary mirror, as described in our Phase Detection Autofocus article. In comparison, mirrorless cameras have to see through the camera sensor, which allows information projected on the sensor to be scanned and analyzed before capture. Today, mirrorless cameras have phase-detection sensors built right on the imaging sensor and once that information is combined with exposure and other relevant data, the possibilities are practically endless. We have already seen how effective face recognition can be on mirrorless cameras, and if manufacturers continue to make improvements in that area, soon enough every image you take will be tack sharp, with the camera automatically focusing on the nearest eye of the person. Some cameras are already capable of recording images before the shutter is released, to avoid taking pictures of subjects with their eyes closed, and we have already seen cameras taking a picture at the moment the subject smiles. You cannot have such advanced intelligence on DSLRs, not until light continuously reaches some kind of imaging sensor. Tracking subjects gets easier with advanced analysis of the scene and the camera can even potentially predict subject movement and its direction.

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