Both types of camera have their advantages and disadvantages. And depending on your field of photography, both systems will work wonders and give you high quality final images.
So why choose one over the other? Read on to find out.
The question of mirrorless vs. DSLR is a common one. Especially for those of us looking for digital cameras beyond the basic point-and-shoots or entry-level.
But how do you choose the right camera for your needs?
The dominance of the established DSLR is being challenged by newer ‘mirrorless’ cameras. They are now in a race to keep the public buying these than slipping into smartphone photography.
The camera’s size is no longer the distinguishing factor. Cameras stand out through the absence of an important component—the flipping mirror.
How does the mirror affect your images? And why is it so important if your camera has one?
Let’s see how a mirrorless camera works compared to a DSLR.
The Sony RX100 Mk III mirrorless camera and the Canon EOS 50D APS-C sensor DSLR
What Is a DSLR Camera?
DSLR stands for ‘Digital Single Lens Reflex’. Before the digital revolution, this would have been called an ‘SLR’. And it solved problems experienced by early photographers.
Film camera photography posed some problems. One of these was the difficulty in seeing beforehand exactly what you were about to record.
The photographer had to rely on a viewfinder which showed a similar but not identical view.
One innovative solution to this problem was the addition of an extra identical lens to the camera system. One through which the photographer peered, and one to form the image on the film.
The Defining SLR Feature: The Mirror
A quantum leap in the design was made when a certain Thomas Sutton patented a novel solution in 1861. He made it possible to compose their shots through the picture taking lens.
Over a hundred years later, the basic idea is still incorporated into modern digital cameras. The most important components of the DSLR are shown in the simplified diagram below.
When the shutter button is pressed, the optical path is momentarily rearranged to look like this:
Once the shutter has exposed the sensor, it closes again ready for the next shot. A spring returns the mirror to its resting position.
A DSLR reads data from the sensor only after an image has been taken. DSLR manufacturers realized the mirror could sit to the side. And still continually reading the sensor.
This continuous stream of image data could then make a video. Or show the view through the lens when composing a photograph.
Canon called this mode ‘Live View’ and it’s now a common feature on many DSLRs.
What Is a Mirrorless Camera?
Any camera without a built-in mirror counts as mirrorless. They generally tend to be much smaller and simpler than the DSLR design.
But the boundaries between mirrorless and DSLRs are not as clear-cut as they once were.
A World War II ‘mirrorless’ spy camera
Modern mirrorless cameras have no optical viewfinder. The only way to see through the lens when composing a photograph is to activate the sensor in a video read mode.
Here, it updates the scene in real time, with a slight delay. Seeing a constantly updated image on the camera’s screen is an intuitive way to compose a photo.
But viewing the image on the camera’s LCD screen drains the battery. The same goes for brighter screen illuminations.
Add to that the mirrorless camera’s appeal as a small pocketable camera body. This places constraints on the battery life.
There is another problem that irks some older photographers using mirrorless cameras. The LCD screens can be difficult to see up close if your vision is not perfect.
What if you want a mirrorless camera but don’t want to be restricted to only using the rear screen? Think about buying a camera with a built-in viewfinder.
The Sony MX100 Mk III is a popular mirrorless camera that packs lots of high-end features. These include an articulated screen and pop-up electronic viewfinder. All fitting into a small rugged case.
But it’s important to be clear about what kind of photography you’re likely to do. To that end, we need to consider some further properties of DSLR vs. mirrorless designs.
Most camera sensors are basically the same. They’re an example of VLSI silicon chips using CMOS technology.
Assuming the sensors use similar technology, there are two statistics that matter. These are the total number of pixels and how much surface area a single pixel has.
These two figures determine the physical size of the sensor’s imaging area. Different digital cameras have different sized sensors.
Smaller image sensors are more cost-effective. And their smaller size meant that the lenses used to form the image could be smaller, lighter and cheaper too.
The market now offers a wide range of different cameras. The statistic that most people tend to compare as a yardstick to quality is the number of megapixels.
But this can be misleading.
Resolution and Pixel Area
Sony RX 100M3, Canon EOS 50D APS-C and 5D MkIII full-frame sensor sizes compared
The sensor used in a full-frame DSLR camera crams 22 million pixels into the same surface area as a 35mm negative. This is the case for the Canon 5D Mark III.
This restricts each pixel to an area of just seven-thousandths of a millimeter (seven microns) square. This sensor will produce a high-resolution photo with 5760 pixels along the long edge.
The Canon EOS 50D is another DSLR but one that uses the smaller APS-C sensor size of 22.3 x 14.9 mm. This fits in almost as many pixels—still enough to make a good A3 sized print but notice the pixel size.
The area of a pixel on the full-frame sensor is over twice that of the APS-C camera’s sensor. We find that the larger the surface area of a pixel in the sensor, the more light it captures.
The more light it captures, the bigger the signal produced for a given level of illumination. The bigger the signal your sensor produces in response to light, the less electrical noise.
For more information on sensor resolution, read here.
If you are looking for more information on crop sensors vs full frame sensors, you need to read this article.
Smaller sensors are not in themselves less sensitive. But they will not perform as well as larger sensors in low light situations.
Recent advances in sensor design have reduced the inherent noise in sensors. The greatest signal-to-noise gains are still to be found in having a large pixel area.
It’s generally true to say that mirrorless cameras have smaller sensors than DSLRs. Because of this, they aren’t so good in low light conditions.
But there is no law of physics to say this must be so. It has more to do with economics and marketing than technology.
Smaller mirrorless camera sales are holding their ground. This is in the face of a generation who think the camera on their phone is good enough.
Full frame mirrorless cameras such as the Sony A6300 have very good low light performance. But electronic viewfinders struggle to produce a bright clean image. Especially in low light conditions.
The conventional DSLR with its optical viewfinder still has a distinct advantage. This comes when shooting in low light.
Autofocus – the Final Frontier
Is your main interest in studio portrait work or landscape photography? Then you’ve used manual focus before.
Sports and wildlife photographers may well have a different perspective. Fast action is difficult to predict. There is often no time to get a shallow depth-of-field focus.
For situations such as this, the autofocus system in the camera is of prime importance.
Some striking developments have taken place in recent years. But there are two still two main methods of autofocusing; contrast and phase detection.
Early mirrorless cameras or DSLRs using Live View had to autofocus. They used a process called ‘contrast detection’.
This works by analysing a part of the image. It checks if there are any sharp transitions between light and dark.
An out-of-focus area will not exhibit high contrast. The edges of objects will be blurred together. And there is less of a difference between light and dark tones.)
But, as focus is attained, edge detail becomes visible. Until the contrast reaches a maximum.
The contrast detection autofocus algorithm then seeks to move the lens. It does this achieve the highest contrast possible in the area of interest.
The problem with this autofocus method is that the camera has no way of knowing which way to move the lens. So it may actually move the lens further out-of-focus before bringing it back into focus.
In practice, this causes the lens to ‘hunt’ for the focus. This makes this method of auto-focus frustratingly slow. Particularly slow if the lens is very defocused.
In its favour, contrast detection is capable of achieving very accurate focusing.
What if your mirrorless camera only has contrast detection autofocus and you want to shoot video?
Forget autofocus altogether. Switch your camera to manual focus and you’ll get better results.
The other autofocus method you’ll find is ‘phase detection’. This works by splitting rays of light from the object. These are then focused into two beams on opposite sides of the lens diameter.
The camera compares how the two beams line up on a special light-sensitive strip. This creates a rangefinder system.
In a DSLR, the optics and electronics for this are at the bottom of the camera.
When the mirror is down in a DSLR, most of the light rays are diverted onto the focusing screen. Here you can see the image and manually focus it.
The autofocus system is housed in the lower regions of the camera. The center of the main mirror is translucent to allow some light to pass through it.
This light is reflected by two further mirrors. It goes onto a chip containing an arrangement of light sensors. Each correspond to an autofocus point in your camera’s display.
The main mirror moves out of the way at the instant the photo is taken. The autofocus sensor can no longer see the scene.
There are situations where the mirror is flipping up and down during continuous shooting mode. The camera’s computer attempts to predict where the subject will be for the next exposure.
Unlike contrast detection, this method can determine which way to turn the focus ring on the lens. There is no hunting back and forth so autofocus is fast and responsive.
Careful design has enabled this combination of optics, mechanics, and electronics. It can achieve autofocus that’s approaching the limits of its performance.
For example, take the Canon’s EOS-1DX Mark II DSLR. It can autofocus while firing off sixteen exposures per second. Impressive though it is, there comes a point where if you move things fast enough, they will break.
Reliability will be an issue if this technology is pushed much further. But this is still the fastest method of autofocusing.
This is why action photographers are still holding onto their top-end DSLRs.
Recent Mirrorless Developments
Mirrorless cameras have gained a reputation for slow autofocus over the years. Especially in low light conditions.
But their performance has been steadily improving.
Truly mirrorless cameras have to do everything using their image sensor. That makes any phase detection built into the image sensor.
This is indeed the case with higher-end mirrorless cameras. These now come with dedicated phase detection pixels built into their sensors.
This has enabled them to take advantage of the speed of phase detection autofocus. And add the fine-tuning accuracy of contrast detection autofocus in a hybrid system.
A note from Josh, ExpertPhotography's Photographer-In-Chief:
Thank you for reading...
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