Over the last decade, you might have noticed television screens getting wider. That's no optical illusion, that's the evolution of television from the 4:3 aspect ratio of the past to the 16:9 widescreen ratio currently used in most media. Before the rise of widescreen, most media was 4:3 aspect ratio, with a standard definition resolution of 640 x 480 (though that number varied, due to the different shapes of pixels in the lines of standard definition TV screens). Now, high-definition media is by default 16:9, with a full resolution of 1920 x 1080, The reason for the shift from lower resolution to higher resolution is obvious: more pixels means you can pack in far more detail. The reason for the shift from 1.33:1 (4:3) to 1.85:1 (approximately 16:9) and beyond is much less obvious, and stems from a similar shift the motion picture industry experienced over 50 years ago.
offers a very good history of the 4:3 and 16:9 aspect ratios. 35mm film, the medium upon which most film is recorded, used the "academy format" in which each frame measures 1 inch by 3/4 inches, or a ratio of 1.33:1, or 4:3. Television was 4:3 as well, and as it became popular (and more viewers stayed home to watch it instead of going to see movies), film studios considered how to provide an experience viewers wouldn't get at home. They produced a variety of widescreen formats, including SuperScope, CinemaScope, and VistaVision, which were wider than the 4:3 standard previously used.
With the rise of 16:9 widescreen HDTVs, home users can finally watch 1.85:1 widescreen movies recorded the way they were intended. The ratios aren't perfect, but are close enough that letterboxing adjustments are negligible. Most HDTVs can adjust the aspect ratios manually, cropping, zooming, and letterboxing video as needed. The next time you see a movie on your HDTV and things look squat or small, or you think you aren't seeing all the details, try changing your screen's aspect ratio display mode. Your nearly perfect video experience might be a button push away.
However, that still leaves the wider anamorphic films out of most consumers' reach. Films recorded in 2.4:1 widescreen force even HDTV owners to deal with either letterboxed or cropped videos. Very high-end home theater systems use projectors that can accept anamorphic lenses, which project a 2.35-2.4:1 image. These lenses are usually mounted on automated sleds, so home users can physically switch between anamorphic lenses for watching movies and standard lenses for watching television shows or other types of videos. These systems can often cost several thousand dollars, and are only found in complex home theater installations.