DSLR vs Mirrorless: understanding the key differences
In this DSLR vs mirrorless comparison we explain the key ways in which compact system cameras differ from DSLRs. We’ll explain how they work, features unique to each and everything else you need to know about DSLR and mirrorless cameras.
Compact system cameras (CSC) are often referred to as mirrorless because, unlike single lens reflex (SLR) cameras they don’t have a mirror to bounce light from the lens up into a pentaprism (or pentamirror) viewfinder.
The fact that this mirror and pentaprism is missing from compact system cameras means that they can be made smaller than digital SLRs.
Compact system cameras differ from compact cameras in that they can accept interchangeable lenses, hence they are part of a system.
DSLR vs Mirrorless: How they work
As already mentioned, digital SLRs have an optical viewfinder which shows the view through the lens after it has been reflected off the mirror and into the pentaprism. The pentaprism flips the image so that it appears the right way around and the right way up in the viewfinder.
Because it sits in front of the sensor in a DSLR, the mirror has to be lifted, and the shutter opened, to allow an image to be captured. The viewfinder is blacked out briefly during the exposure.
Once the exposure is complete and the shutter closed, the mirror flips back down into place and the scene becomes visible in the viewfinder once more.
The only barrier to light between the lens and the sensor in a CSC is the shutter curtain. This opens to reveal the sensor so that a live view feed can be sent to the electronic viewfinder or the screen on the back of the camera.
However, it must close and then quickly open again for the duration of an exposure to take a shot, before closing and reopening. Some compact system cameras also have an electronic shutter, which effectively works by taking a snippet of the live view feed.
As this doesn’t require mechanical movements, an electronic shutter usually enables faster shutter speeds than a normal shutter curtain.
DSLRs can also show a live view image on their rear screen, but just like when taking a shot, the mirror has to be lifted out of the way.
The fact that this mirror and pentaprism is missing from compact system cameras means that they can be made smaller than digital SLRs.
Compact system cameras differ from compact cameras in that they can accept interchangeable lenses, hence they are part of a system.
DSLR vs Mirrorless: How they work
As already mentioned, digital SLRs have an optical viewfinder which shows the view through the lens after it has been reflected off the mirror and into the pentaprism. The pentaprism flips the image so that it appears the right way around and the right way up in the viewfinder.
Because it sits in front of the sensor in a DSLR, the mirror has to be lifted, and the shutter opened, to allow an image to be captured. The viewfinder is blacked out briefly during the exposure.
Once the exposure is complete and the shutter closed, the mirror flips back down into place and the scene becomes visible in the viewfinder once more.
The only barrier to light between the lens and the sensor in a CSC is the shutter curtain. This opens to reveal the sensor so that a live view feed can be sent to the electronic viewfinder or the screen on the back of the camera.
However, it must close and then quickly open again for the duration of an exposure to take a shot, before closing and reopening. Some compact system cameras also have an electronic shutter, which effectively works by taking a snippet of the live view feed.
As this doesn’t require mechanical movements, an electronic shutter usually enables faster shutter speeds than a normal shutter curtain.
DSLRs can also show a live view image on their rear screen, but just like when taking a shot, the mirror has to be lifted out of the way.
DSLR vs Mirrorless: Optical vs electronic viewfinders
The first electronic viewfinders were pretty terrible and this has made many photographers wary of them. However, things have improved enormously over the last couple of years.
Although the contrast and colour of the image in an EVF usually makes you aware of the fact that you are looking at an electronic image rather than through an optical finder, there’s usually plenty of detail visible.
There are also some significant advantages to using an electronic viewfinder. The most significant is that the exposure, colour and white balance settings are all taken into account, so you see the image as it will be captured. If you reduce the exposure you will see the image darken, and if you select the monochrome mode you’ll see a black and white image.
Another advantage to an electronic viewfinder is that the image can be magnified and this makes focusing manually easier.
The main downside to using an EVF is that even with the image review turned off there is often a slight lag when shooting continuously and this can make it hard to follow a moving subject.
However, things are improving all the time and while an EVF might not be ideal when shooting sport, it is possible to photograph action with a CSC.
Some photographers also don’t like the fact that they see a processed image in an EVF rather than an unadulterated view of the scene.
The first electronic viewfinders were pretty terrible and this has made many photographers wary of them. However, things have improved enormously over the last couple of years.
Although the contrast and colour of the image in an EVF usually makes you aware of the fact that you are looking at an electronic image rather than through an optical finder, there’s usually plenty of detail visible.
There are also some significant advantages to using an electronic viewfinder. The most significant is that the exposure, colour and white balance settings are all taken into account, so you see the image as it will be captured. If you reduce the exposure you will see the image darken, and if you select the monochrome mode you’ll see a black and white image.
Another advantage to an electronic viewfinder is that the image can be magnified and this makes focusing manually easier.
The main downside to using an EVF is that even with the image review turned off there is often a slight lag when shooting continuously and this can make it hard to follow a moving subject.
However, things are improving all the time and while an EVF might not be ideal when shooting sport, it is possible to photograph action with a CSC.
Some photographers also don’t like the fact that they see a processed image in an EVF rather than an unadulterated view of the scene.
DSLR vs Mirrorless: Auto focus
Most DSLRs can use contrast detection AF when they are in Live View mode and the image is being composed on the main screen. It is also usually possible to use the phase detection AF system, but the Live View feed is interrupted while the focusing takes place as the mirror has to drop back into position in front of the imaging sensor.
Some compact system camera manufacturers have now started to use hybrid focusing systems which combine the accuracy of contrast detection with the speed of phase detection.
This is achieved by making some pixels on the imaging sensor phase detection receptors. In some cases these pixels are also used to make up the image, but in others they are just used for focusing.
Canon has also introduced hybrid focusing to some of its recent SLRs for use in Live View and video mode.
The contrast and hybrid autofocus systems inside compact system cameras generally operate faster than the contrast detection AF systems employed by SLRs in Live View mode.
Most DSLRs can use contrast detection AF when they are in Live View mode and the image is being composed on the main screen. It is also usually possible to use the phase detection AF system, but the Live View feed is interrupted while the focusing takes place as the mirror has to drop back into position in front of the imaging sensor.
Some compact system camera manufacturers have now started to use hybrid focusing systems which combine the accuracy of contrast detection with the speed of phase detection.
This is achieved by making some pixels on the imaging sensor phase detection receptors. In some cases these pixels are also used to make up the image, but in others they are just used for focusing.
Canon has also introduced hybrid focusing to some of its recent SLRs for use in Live View and video mode.
The contrast and hybrid autofocus systems inside compact system cameras generally operate faster than the contrast detection AF systems employed by SLRs in Live View mode.
DSLR vs Mirrorless: Extra features
Compact system camera and DSLR manufacturers introduce features such as Wi-Fi and NFC (Near Field Communication) connectivity with each new model to make them more attractive to purchasers. But there are some that are being added to CSCs as a direct result of the mirrorless design.
Focus Peaking, for example, highlights the areas of highest contrast (and therefore best focus) to make it easier to adjust focus manually when shooting video, but it can also be useful when shooting stills.
A Zebra display can also indicate areas that are close to burning out with flashing lines. Like Focus Peaking, this relies on the live view feed to operate.
Olympus CSCs also have a feature called ‘Live Bulb’ and ‘Live Time’ which enable you to see the image build up on the camera screen (or a smartphone connected by Wi-Fi) during long exposures.
Compact system camera and DSLR manufacturers introduce features such as Wi-Fi and NFC (Near Field Communication) connectivity with each new model to make them more attractive to purchasers. But there are some that are being added to CSCs as a direct result of the mirrorless design.
Focus Peaking, for example, highlights the areas of highest contrast (and therefore best focus) to make it easier to adjust focus manually when shooting video, but it can also be useful when shooting stills.
A Zebra display can also indicate areas that are close to burning out with flashing lines. Like Focus Peaking, this relies on the live view feed to operate.
Olympus CSCs also have a feature called ‘Live Bulb’ and ‘Live Time’ which enable you to see the image build up on the camera screen (or a smartphone connected by Wi-Fi) during long exposures.