Live preview

Live preview is a feature that allows a digital camera's display screen to be used as a viewfinder. This provides a means of previewing framing and other exposure before taking the photograph. In most such cameras, the preview is generated by means of continuously and directly projecting the image formed by the lens onto the main image sensor. This in turn feeds the electronic screen with the live preview image. The electronic screen can be either a liquid crystal display (LCD) or an electronic viewfinder (EVF).

The concept for cameras with live preview largely derives from electronic (video) TV cameras. Until 1995 most digital cameras did not have live preview, and it was more than ten years after this that the higher end digital single-lens reflex cameras (DSLR) adopted this feature, as it is fundamentally incompatible with the swinging-mirror single-lens reflex mechanism.

The first digital still camera with an LCD for autogain framing live preview was the Casio QV-10 in 1995.

The first prosumer camera to use live view for both exposure simulation live preview ES-LV control and live preview framing was the fixed-lens Canon PowerShot G1 from 2000 (possibly the first was Canon Powershot Pro70 in 1998), although this was still in the line of compact cameras.

The first DSLR to use live view for framing preview only, like early other live view but non-mirrored digicams, was the fixed-lens Olympus E-10 from 2000. The first interchangeable-lens DSLR to use a live preview for framing was the Fujifilm FinePix S3 Pro, which was launched in October 2004. Its "Live Image" mode could display a live, black-and-white framing preview of the subject that could be magnified for manual focusing purposes, although the preview was limited to a duration of thirty seconds.

...
Wikipedia