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DSLR vs Mirrorless. The differences.

09. January 2018

Are DSLRs, with their bulky bodies, really cameras from the past, and are mirrorless cameras the future of photography? There is no straight answer to that. Let’s look at the differences between them and strength of each other.

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What is a DSLR?

Modern DSLR’s as well as old analog 35mm SLR’s share the same concept. The light is coming in through the lens, which is then reflected by a mirror up into the viewfinder. The light is actually passed through a pentaprism, so you can see the image in its original orientation. Otherwise you would see the image upside down, like you would get in old large format cameras.

If you press the shutter button, the mirror flips up out of the way, and the light is passed through directly to the image sensor, which then captures the final image.

What is a Mirrorless Camera?

Simply speaking, the Mirrorless Camera is a DSLR without the mirror.

Mirrorless cameras are on the market in all shapes and sizes. Compared to DSLR’s, they have one thing in common: They don’t have a flip up mirror. Strictly speaking, you most likely have a mirrorless camera already: All smart phone cameras are mirrorless, and most point and shoot models too.

In mirrorless cameras, the light is passed through the lens, directly onto the chip. There is no mirror in between to pass it to the viewfinder. In mirrorless systems, the viewfinder is also exchanged with a small display - so you see exactly the same image in your view finder as well as on your camera display.

If you are using Live View in your DSLR where you look at your LCD instead of through your viewfinder, you already use your DSLR like a mirrorless camera to some extent.

Differences

Now let’s look at the differences between DSLR’s and mirrorless cameras. While both systems actually use the same full frame or APS-C sensors, neither one of the systems has a benefit regarding image quality per se.

Portability

Perhaps one of the most obvious differences between DSLRs and mirrorless cameras is their size. The light reflecting mirror and the pentaprism is no longer needed in mirrorless systems, so that reduces size and weight.

The space between lens and camera on DSLRs is much larger because of the mirror, so the architecture of the lens need to compensate that. Since the distance between lens and camera can be reduced a lot, lenses can be recalculated and made smaller too. Still many manufacturers are building mirrorless lenses just by bridging the space between, but in the time to come we will certainly see more and more lenses for mirrorless systems, which make use of this advantage.

  • Fit more gear in your bag: While you might have had one camera in your bag, you can now easily fit two cameras in your bag, to be more flexible at your shootings.
  • Holding your camera for a long time might now exhaust as much as before, as the camera is smaller and does not weigh as much.
  • For street photography, mirrorless cameras are not as obtrusive as DSLR’s, that might be a benefit for your shooting style too.

While I do prefer the much smaller camera for these reasons, it’s up to your personal preference if this is as relevant to you. Larger and heavier lenses look funny on these small cameras, and they might feel more unbalanced in your hand. If you like the benefits of a mirrorless system but like larger bodies, most brands offer grips to be attached to the camera, which also provide additional battery power at the same time.

As a landscape photographer you can not just save weight on the camera, but could also on the tripod. As the overall weight is less then with DSLR’s, you might want to use a lighter tripod.

Adapting other lenses

To adapt other lenses, mirrorless cameras have a huge benefit. Because of the architecture of a DSLR, there is a lot of distance between the sensor and the lens, which is reserved for the mirror to either reflect light up into the viewfinder, or to flip up and let the light pass onto the sensor. Mirrorless cameras don’t have that, so the distance can be much smaller between sensor and lens.

Now if you want to adapt lenses for the Canon or Nikon mounts, it can be done easily by adding an adaptor to the specific mount. The adaptor only bridges the space from the smaller so-called flange distance, the distance between sensor and lens, to the larger distance needed by either mount. As it is only a spacer, it does not contain any additional glass elements, so adapting lenses is basically lossless.

By adapting lenses, a huge number of lenses is available for your mirrorless system, and you are not bound to the lenses of your specific brand or lenses made specifically for that lens mount.

Things to consider:

  • Autofocus: Adapted lenses might not provide the same auto focus features. While in terms of optics the adaption is lossless, the electronics are a different story. Depending on the lens and the adaptor, certain autofocus features might not be as fast as native lenses or not available at all.
  • Vintage lenses: Mirrorless cameras often provide focus assisting features, which are provided by the camera, not so much by the lens. Using mirrorless cameras, features like focus peaking or focus magnification are also available for old vintage lenses. Because of that, mirrorless cameras make it even easier to focus old lenses.

EVF - The electronic viewfinder

In the early days of mirrorless cameras, there wasn’t a viewfinder. Serious photographers would not even consider mirrorless cameras because of that. This has changed over time, and the added electronic viewfinder is getting better and more powerful.

The main difference is that in DSLR’s, you look through a pentaprism and see the real image through the lens. The EVF records the image with the sensor and renders it on a small LCD inside the viewfinder - and on the display on the back of the camera.

The overall benefit of the EVF is, that it is a rendered image. It is now possible to add all sorts of information on top of the image. Of course, you can show the usual information like aperture and ISO.

  • You can include any clipping warnings right inside the image, including the area of the images it relates to. Sony does that with its zebra feature.
  • You can zoom an image easily, which supports you by focusing on certain details in the image.
  • You can add image effects to your image. I like enabling black and white for street photography. So, I can see the image in black and right up front, not after taking the shot. That helps a lot to estimate how the contrast of the image works out. By the way: If you shoot RAW, you still get all the information of a coloured image too.
  • As the image is rendered through the chip already, you will be able to see the image already before you take the shot, with the same aperture, lighting and all the other settings.

But there are some limitations still:

  • The EVF is slower than the optical viewfinder. It’s not that I would see a major difference on the latest models like the a7R III, but there is a slight lag. In practical terms, I never noticed really that this is an issue. This is more prominent in darker situations though.
  • Shooting in low light, sometimes it’s easier to see the image in an optical view finder. But this really depends on the case. In very dark situations you even see more in an EVF as through the sensitivity of the sensor, you’re able to actually see something, while the optical viewfinder is already very dark. Of course, the darker it gets, the more grainy the image in the viewfinder is.

Autofocus performance

In the early days of mirrorless cameras, the implemented autofocus system was pretty similar to how compact cameras work. In practical terms, the camera would read out the image sensor, while the lens moves through its focus range to the point where the contrast is the highest at a certain point. This is called contrast detect autofocus. The good thing about this method: It is very accurate. The bad thing is: It is very slow. While compact cameras have such small lenses, focusing is much more efficient with those compared to the much larger lenses of mirrorless cameras.

In opposite, DSLRs focused with something called phase detect autofocus, which is much faster than contrast detect AF. However, on DSLRs the sensor to measure and calculate phase detection is a separate sensor from the image sensor, and less accurate because of that.

The solution is to combine both methods on the image sensor and get the best of both worlds. Modern cameras in both systems are implementing this by now, in most cases it is called Hybrid AF, as it combines contrast detection as well as phase detection.

The result of all this is that the gap in focusing performance between mirrorless cameras and DSLRs is getting smaller. Mirrorless cameras were not considered to be ready for sports photography. Actually, Sony proves us wrong: With the publication of the A9, they got a mirrorless camera, which has a faster focusing performance even without blackouts in the viewfinder compared to Nikon and Canon flagships.

Focus assistance: Focus Peaking and Zooming

For manual focussing mirrorless cameras can provide even more assistance, which DSLRs cannot provide to this extend.

As the EVF shows the rendered image from the sensor, there are no intermediate parts in between. The full image can be used for further analysis. This is used for focus peaking. If you switch your mirrorless camera to manual focus, the camera can zoom into the area of interest as well as mark the parts which are in focus with a given colour. This way it is very easy to focus manually.

The good thing is: This is not tied to special lenses of the manufacturers ecosystem. Using adaptors for lenses made for other mounts are available, especially even old vintage lenses can be used in the same way.

For landscape photography, where manual focussing is an integral part of the daily work, this comes in very handy. With focus peaking and zooming into the picture, you have much more control.

Previewing images

Looking through the optical viewfinder, you will see exactly the same picture as what the lens is providing, but with the closed down aperture if applicable already. DSLR’s close the aperture to its real value only while taking the photograph, or if you specifically want to preview the image in the correct aperture - which tends to get really dark. This is different for the electronic viewfinder, as it is stopped down already. The whole image is rendered through the chip already, so you pretty much see the result already before taking the picture. You can see in real-time the effect of changing iso, aperture or exposure time. Of course, long exposures will come out different, as what you see in the EVF is still a live picture.

Battery life

Basically, DSLRs and mirrorless cameras are using about the same amount of power to take the images. The difference is in how you look at the images. With an optical view finder, you don’t need much power at all, as it is as the name states just optical. If you look through your electronical viewfinder or at your display on the back of your camera, you need power to actually see something. The more you use either of those, the more charge you use up in your camera.

The other reason why the battery life is poor is based on mirrorless camera manufacturers trying to make those cameras very small, so the batteries also tend to get very small too compared to DSLRs.

The battery live of mirrorless cameras was rather poor. This has been improved by Sony in their latest camera line up already: While the older Sony a7R II and the a6000 series holds up for about 250-350 shots per charge, the successor, the a7R III, does easily 650 shots and more. Still comparing this to flagship DSLRs, this is a rather small number. Good DSLRs can even do 2000 pictures with one charge, or even more.

For me this has never been an issue, as I kept charging my camera with a power bank as long as it was in my camera bag. Still I would either disable the display of the camera when doing timelapse, or add a power bank to power the camera right away, so this is not an issue for longer shootings.

Silent shutter

There is one more feature I really like in mirrorless cameras, which is the silent shutter. While in DSLRs, you certainly have some mechanical parts which make noise, you can reduce that by locking up the mirror and using live view or similar features. Mirrorless cameras provide this natively.

Mirrorless cameras can often choose between mechanical and electronic shutter. While both having their benefits, for me the largest benefit is that I can choose a silent shutter, which is especially handy in public performances. Even shooting portraits I like using it. People just don’t know that I shoot pictures already and stay comfortable. Often these images turn out better working with them on posing while telling them it’s just preparation.

Silent shooting / electronic shutter introduces some problems like with special lighting or moving objects, but this is too much detail for this overview and worth another article.

Final thoughts

It seems very likely, that both systems will coexist for much more time. Both systems have their benefits and limitations individually. The image quality, which is certainly the most important factor, is not better in either system.

For me personally, mirrorless systems are much more interesting, because it offers some features I don’t get in DSLRs yet. The mirrorless market is certainly the more innovating market these days, but some of the features are already implemented in DSLRs too. Live view in DSLRs is getting more powerful too. Certainly, there is an overlap between both systems.

Also, many people are already invested in either system. In case adapting lenses is not an option because of lack of performance, it is not an easy switch to make. There is a huge chance for Canon and Nikon to publish their own mirrorless systems based on their current lens line-up and keep up with the innovation. I don’t see a reason why we should stick to the much more complex DSLRs technology wise and would expect to have a shift over to mirrorless in the coming years.

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