Seeing this exhibition had me thinking: How would this look for a mirrorless camera? What's in a mirrorless camera, anyway? Obviously, it contains a lot of the same items: The battery, the imaging sensor, an LCD/OLED display for viewing images and menus, shutter buttons and wheels, a tripod mount, and so on.
It's probably easier to answer the question: What's not in a mirrorless camera. For a start, it doesn't have a mirror, that's given by the name.
Here are a couple of very simple illustrations of DSLR and mirrorless cameras, illustrating that the DSLR has a mirror between the lens and the sensor, and a pentaprism. While, on the other hand, the mirrorless camera has a shorter register distance, the distance between the lens mount and the sensor plane.
DLR camera with lens:
Mirrorless camera with lens
But the lack of the mirror is not the only difference. Let's try to make a summary of the main differences between a DSLR camera, and a mirrorless camera:
|Feature||DSLR camera||Mirrorless camera|
|Phase difference autofocus (PDAF) sensors||Yes||No, the imaging sensor is used for autofocus|
|Light metering sensor||Yes||No, the imaging sensor is used for metering|
|TTL flash sensor||Yes, can be the same as the light meter||No, the imaging sensor is used for TTL flash metering|
|Contrast detection autofocus (CDAF) processing, liveview||Mostly||Yes|
|Video recording and microphone||Mostly||Yes|
|Electronic eye-level viewfinder (EVF)||Only Sony SLT cameras||Some|
Mirrorless cameras use CDAF for focusing, and liveview for viewfinding, rather than the optical path through the mirror and pentaprism, in the DSLR cameras. However, DSLR cameras are expected to do the same nowadays, so it's not like this is exclusive to mirrorless cameras. The same goes for video recording: This is also expected from DSLR cameras.
Some mirrorless cameras add an EVF, an eye-level electronic viewfinder. Examples include the Panasonic G and GH series, the Olympus OM-D, the Nikon V1 and V2, the Sony NEX 6 and 7. This technical feature is generally not found in DSLR cameras, with the exception of the Sony SLT family of cameras, which use a fixed, semi-transparent mirror, and replaces the pentaprism viewfinder with an EVF.
Hence, we see that mirrorless cameras lack some technical features found in DSLR cameras, but they don't add any new. For that reason, they are simpler, and contain less components. And they should be cheaper to produce and require less maintenance.
The latter is not to be ignored. Since the digital revolution, you can find old second hand SLR and rangefinder cameras available at low prices. However, while they may appear to operate flawlessly, they may require very expensive cleaning and lubrication to operate safely over some period.
With less mechanical components inside the mirrorless cameras, they can be expected to require less maintenance. Some time in the future, they will come with "global electronic shutters", and can drop the mechanical shutter as well, further simplifying the design.
So why are mirrorless cameras not cheaper to buy, since they are simpler? Interviews with industry insiders say that the DSLR mirror box is "mature technology". In business-speak, this means that they are very cheap to produce. They don't add much to the production cost.
On the other hand, DSLR cameras have been around a long time, people know what to expect from them. Mirrorless cameras, on the other hand, are more of an unknown, and for that reason, there has been a smaller market for them. Add to this the research and development cost for the new mirrorless technology, and you have the reason why mirrorless cameras are still not cheaper than DSLR cameras.
In the future, though, as mirrorless cameras grow in volume, they should be cheaper and require less maintenance, which is good for us consumers.
One big problem with mirrorless cameras so far, is that they generally have an appalling continuous autofocus (AF-C) performance, as compared with premium DSLR cameras. The Nikon 1 series of cameras try to fix this by adding PDAF sensors on the imaging sensor. However, I don't think this makes much of a difference yet.
In the mean time, people who need a very good AF-C performance, e.g., for photography of sports or birds, must still stick with DSLR camers.