Projection problems on an event usually come from one of three guesses: a screen that is too small for the back row, a projector placed where the lens cannot fill the screen, or a lumen figure picked from the brochure. This calculator does the three sums on one page.
What it covers
The first part gives screen height, width and diagonal from the distance to the furthest viewer. You choose the content: video and big graphics, slides with text, or fine detail such as spreadsheets. Smaller text needs a bigger image for the same back row.
The second part gives the range of distances at which the projector can sit, from its throw ratio range. Enter the zoom limits from the spec sheet. If the position you have is outside the range, you need a different lens or a different projector.
The third part gives the lumens needed to hold a chosen image contrast in a given amount of ambient light. It includes 20% headroom, because projectors lose output with age and give some away in colour-accurate modes.
When to use it
Use it at the quoting stage for breakout rooms, plenary screens and hybrid sets, and again when a venue's house projector is offered. A light meter reading at the screen gives a better answer than any preset, so take one on the recce if you can.
How it works
Image height is the furthest viewer's distance divided by 8 for video and big graphics, 6 for slides with text, or 4 for fine detail. These are common rules of thumb. Width is height multiplied by the aspect ratio, and the diagonal follows from Pythagoras, shown in metres and inches.
Throw distance is the throw ratio multiplied by the image width, calculated for the shortest and longest ratio of the zoom range. It is measured from the lens to the screen.
Lumens needed = (target contrast ratio - 1) x ambient light on the screen in lux x image area in square metres / screen gain. The contrast targets are based on the four categories in AVIXA's image contrast ratio standard (Image System Contrast Ratio, which revises ANSI/INFOCOMM 3M-2011): passive viewing 7:1, basic decision making 15:1, analytical decision making 50:1 and full motion video 80:1. The AVIXA page names the four ratios but the standard itself is paid, so the values here are checked against a published summary of it.
The sum ignores the projector's own black level, so it is a planning figure. It also takes the lumens as reaching the screen, so use ANSI lumens from the spec sheet. A measured lux reading at the screen is better than an ambient preset.
Rather we did the paperwork?
Send the client brief and floorplan to Production Office and get back the kit list, signal flow, crew plan and schedule, checked by a broadcast engineer, with nothing of ours on it.