A brief history of mirrorless cameras
A mirroless is a digital camera with interchangeable optics, characterized mainly by the absence of a movable mirror that allows showing what is reaching the camera through the lens. Instead, the sensor itself generates an image that is sent to the viewfinder and/or the corresponding screen.
With every passing day, it becomes one of the most popular options, reaching some classic DSLR camera manufacturers in important markets, such as the American one.
Although today's most popular mirrorless are inspired by the DSLRs that have dominated the market for decades, the first digital mirrorless camera was originally an evolution of telemetric cameras like the Leica M.
The telemetric system popularized by Leica, allowed two images to be superimposed and matched by automatically calculating the focus distance by triangulation and this was translated into the camera's focus system. In the absence of a mirror system such as DSLR, the vibration that such a mirror would cause is disregarded, providing sharper images with longer exposure times.
Although the parallax between the image captured by the sensor and what is seen by the viewfinder meant that it was not the best option depending on what type of photography, telemetric cameras were for many years more popular than the SLRs that took time to catch the market’s attention. And this was not until photometry systems began to be integrated through the lens, as in the first Pentax Spotmatic cameras.
The first digital rangefinder (and therefore the first modern mirrorless camera) was the Epson R-D1 in 2004, which was followed shortly thereafter in 2006 by Leica with its M8.
Of course, at that time almost all the sensors were CCD, which provides excellent color reproduction, but did not allow something that we now take for granted, seeing the image that reaches the sensor live, at least on photographic cameras. So, for a few years the only mirrorless were rangefinders that had a system that allowed focusing and framing without using a prism.
Around 2008, Olympus and Panasonic presented the Micro 4/3 system, which represented an evolution of the 4/3 system for DSLR, sharing very similar if not the same sensor specifications. The biggest difference is the elimination of space for a mirror and a pentaprism, reducing the flange focal distance (the distance from the mount to the focal plane) to about 19.25mm. This reduced distance allowed to practically adapt any type of lens to the new mount, which provided versatility that the SLR system does not have.
This, added to a sensor with CMOS technology allowed to design cameras more similar to what we have today, making both companies the main manufacturers of mirrorless cameras for many years, ahead of other manufacturers.
Of course, this type of cameras still had many disadvantages over DSLRs, the most popular product among professionals. The main ones being the image quality of the CMOS versus CCD sensors and the autofocus. The first disadvantage was quickly overcome, with the CMOS technology being improved very quickly, which soon replaced the CCD in most camera models, including the Top of the range DSLR. In addition, being able to offer advanced video options thanks to the sensor change was what convinced everyone for the change and what brought the mirrorless closer to the professional market.
Although there were already cameras without a full-sensor mirror, like the Leica, it was not until Sony's arrival on the market that it ended up catapulting this category of cameras to the level it is today.