Projector Throw Calculator

Multiply the picture width by the projector's throw ratio. A throw ratio of 1.5 with a 10-foot-wide picture puts the lens 15 feet from the screen. With a zoom lens there is a range, from the shortest ratio to the longest, and anywhere inside it works — the calculator shows the range for your screen and where the zoom sits at the distance you choose.

Lens shift moves the picture up, down or sideways without tilting the projector, so the image stays rectangular. It is usually quoted as a percentage of the picture's height or width. The calculator shows how much shift your lens height and position need against what the lens allows, and the range of heights the lens can sit at.

Usually not. Most makers say so outright: the maximum vertical shift shrinks as you use horizontal shift, and the other way round. Their charts draw the range as a shape — Epson's as a diamond, straight lines between the two maximums; JVC's as a curve that reaches a little farther into the corners.

The tool checks both directions together, against that shape. Choose your projector from the list and it uses the maker's own range; enter one by hand and it assumes the diamond, the most cautious shape, with wider safety margins. If your projector's manual has a shift chart, it is worth a look before you fix the mount.

Roughly the projector's light output, times the share of the panel the picture uses, times the light its lens still passes at that zoom setting, times the screen's gain, divided by the picture's area. The tool gives the result in foot-lamberts and nits. Digital cinema's reference white is 48 nits, about 14 foot-lamberts.

Start from an honest lumen figure. The two standard measurements are ISO 21118 and ANSI lumens, and reputable makers rate to one of them. Some projectors are sold on “LED lumens”, “light source lumens” or plain “lumens” with no standard named — figures that can be several times what the projector puts on a screen. If a spec sheet does not name ISO or ANSI, treat its number with suspicion, and the brightness worked out from it will be too high.

Even an honest rating is a best case, measured in the projector's brightest mode; a calibrated picture mode is often well below it. Use a measured or calibrated figure when you have one.

No — a projector can zoom a letterboxed picture to fill a 2.40:1 screen, and zoom back down so a 16:9 picture fills its height, recalling each with its lens memory. That takes a longer throw ratio for 16:9 from the same place, so the projector must sit where its zoom reaches both; the tool shows both ranges and where they overlap, and a short zoom may not reach both from anywhere.

An anamorphic lens, used with the projector's or a processor's anamorphic mode, uses the whole panel instead of leaving the letterbox bars dark, which puts noticeably more light and more pixels on the picture. Lenses come in two kinds: some widen the image (horizontal expansion), others squeeze its height (vertical compression); each has a minimum throw distance and prefers the projector centered on the screen. The tool models both from the lens's own figures.

Either way, a video processor makes it easy: it detects each film's aspect ratio as it plays and fits it to the screen — a scope film filling it, a 16:9 show at its full height — so nobody has to change a setting.

It depends on the projector's panel and on how the lens works. To make a 2.37:1 picture, a lens either widens the picture or squeezes its height. A widening lens (horizontal expansion) needs 1.33× on a 16:9 panel and 1.25× on a 17:9 one — the 4096-pixel-wide panels many home cinema projectors use. A squeezing lens (vertical compression) needs 0.75× and 0.80×. In the tool, a factor over 1 widens and one under 1 squeezes.

The two kinds place the projector differently. A widening lens makes the projector's own picture narrower before the lens spreads it, so the projector sits closer to the screen for the same picture; a squeezing lens keeps the picture's width, so the throw distance stays as it was without the lens. Makers of both kinds quote more light than letterboxing — commonly about a fifth more for widening designs and up to a third or more for squeezing ones.

Whichever you choose, check the lens's minimum throw distance, often around 1.4 to 1.6 times the screen's width: any closer and the picture's edges bend. Enter the lens's own factor, minimum throw and light transmission from its maker's spec sheet, and the tool works out the rest.

A 16:9 signal is 3840 pixels wide. On a 4096-wide panel shown pixel for pixel, the extra columns stay dark, so the image the projector throws is wider than the picture. With a video processor scaling the picture to the whole panel width, the full panel's image is the screen's width — a slightly different zoom setting — and the light from those columns lands on the picture.

It can, when the projector sits low or behind a raised row. The beam's lower edge runs from the lens to the bottom of the picture; anyone whose head reaches above that line casts a shadow. The calculator checks every seated head in the room — reclined rows included — and says which one is closest and by how much. Placed automatically without a room, the projector keeps the beam’s lower edge 12 in. above the heads where its lens shift allows — room for a tall viewer sitting up — and as high as it can where it does not.

The screen material's specification states its gain: 1.0 is a matte white that reflects evenly in every direction. Higher-gain materials return more light toward the seats in front of them and less to the sides; acoustically transparent fabrics are often below 1.0. Enter your material's figure for the brightness estimate.