Mirrorless interchangeable-lens camera

A mirrorless interchangeable lens camera (MILC) is a digital camera with an interchangeable lens. A mirrorless camera uses an image sensor to provide an image to the electronic viewfinder (EVF). It is called mirrorless since it does not have a movable mirror in the optical path.

Compared to single-lens reflex cameras (SLR), mirrorless cameras can be made simpler, smaller and lighter because they do not have an optical viewfinder. Such a viewfinder is composed of a mirror housing, a movable mirror, or a viewing prism with reticle. Neither do they need a secondary autofocus mirror, an autofocus sensor array and a separate light metering sensor.

Since mobile phones with cameras, compact cameras, superzoom cameras today all are mirrorless cameras, it is essentially only the DSLR cameras, with emphasis on the R (Reflex) which are cameras with movable mirrors.

Mirrorless cameras have until recently had two challenges keeping them from competing with top of the line DSLRs. The initial challenge was to provide an EVF with the resolution, clarity and response of direct optical viewing. The second challenge has been that the contrast detect autofocus (CDAF) initially used in mirrorless cameras requires about twice the time to acquire focus compared to that of phase detect autofocus (PDAF). Professional photographers covering sports and news events have therefore been among the last to embrace the mirrorless cameras. The latest generation mirrorless cameras, however, have PDAF pixels built into the image sensor offering fully competitive and accurate autofocus and many times faster continuous shooting with continuous autofocus than DSLRs.

With high quality images being available even from smaller sensors a new distinction other than camera price is available to photographers. As a rule, to professionally photograph studio objects, landscapes or architecture requiring rich and realistic images, a camera with a full frame or a medium format sensor is preferred. Lenses required and used for this are typically in the 20 to 200 mm focal range. With the same requirement for image quality, sports and wildlife photography then requires focal lengths from 600 to 800 mm or more. Mirrorless system cameras with smaller, high resolution sensors can here offer the advantage of the same final image coverage using shorter focal length, lighter lenses because of the so-called "crop factor" of the smaller sensor. This of course requires that the smaller sensor has a high enough pixel density to offer a final resolution equal to or better than what can be cropped out of the image from a larger sensor using the same, shorter focal length lens.

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