1. The aspect ratio of a screen or image is the ratio of its width to its height. Almost all flat-panel TVs, home-theater projectors, and HDTV content have a native aspect ratio of 16:9, aka 1.78:1, while most movies are wider with a native aspect ratio of 1.85:1 or 2.39:1. A few flat-panel TVs have a native aspect ratio of 21:9, aka 2.33:1.
2. If you watch both movies and TV shows, the aspect ratio of the image and screen won’t always match; when they don’t, you will see black bars above and below or to the sides of the image, as shown above.
3. With flat panels, this is unavoidable unless you use one of the TV’s “zoom” functions, which either distort or crop parts of the image. I don’t recommend this; learn to live with the black bars to see the image as the content creator intended.
4. Many projector owners get a 2.39:1 or 2.35:1 screen so that widescreen movies fill the screen without significant black bars.
5. One way for a 16:9 projector to fill a wide screen with a widescreen image is to zoom the lens so the active image area fills the screen. Some projectors have several “lens memories” that let you store and recall the zoom, focus, and lens-shift settings for content with different aspect ratios.
6. The other way for a 16:9 projector to fill a wide screen with a widescreen image is to use an anamorphic lens, which optically stretches the image horizontally while the projector electronically upscales the image vertically. For 16:9 content, the anamorphic lens can be moved out of the way, or in the case of a fixed lens, the projector can electronically scale the image to the correct aspect ratio. This approach is more expensive than zooming, but it uses all the projector’s pixels, giving the image more resolution and making it brighter.
7. There are various formulas to calculate the optimum seating distance; for the purpose of this list, I will use the ITU (International Telecommunications Union) recommendation of 3 times the screen height for HD and 1.5 times the screen height for UHD/4K, regardless of the screen’s aspect ratio.
8. The size of virtually all display screens is specified by their diagonal measurement. For 16:9 screens, the height is about half the diagonal measurement; for 2.39:1 screens, the height is about 0.4 times the diagonal measurement.
9. If you know your screen size, you can calculate the optimum seating distance:
(seating distance) = 3 x (screen height)
For example, a 16:9 screen measuring 70 inches diagonally has a height of about 35 inches, so the optimum seating distance for HD is 105 inches or 8.75 feet; for UHD/4K images, the optimum seating distance is 52.5 inches or 4.4 feet. These seating distances are the same for a 2.39:1 screen measuring 88 inches diagonally, because the height of the screen is still 35 inches.
10. If you know your seating distance, you can calculate the optimum screen size you will need:
(screen height) = (seating distance)/3
For example, if your seating distance is 10 feet (120 inches), the screen height for HD should be 40 inches, which translates to a diagonal measurement of 80 inches for 16:9 or 100 inches for 2.39:1. For UHD/4K, the screen height should be 80 inches, which translates to a diagonal measurement of 160 inches for 16:9 or 200 inches for 2.39:1.