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HELPFUL INFORMATION ABOUT PROJECTION & SCREENS:

A Guide To Setting Your Projection Screen Correctly

 

Screen Size:
The screen should fit to the audience, not to the projector!

The Four-Six-Eight Rule -468-

The standard rule of thumb for sizing images is the four-six-eight rule -468-. The farthest viewer should be no more than four, six or eight times the image height away from the screen. Which of the three options depends on the following:

-   four times is for material with fine details like CAD drawings or other detailed graphics

-   six times is for detailed reading (spreadsheets or text with images)

-   eight times is for watching a movie or images

 

 

The minimum distance from the projection screen to the first row of seating should be at least 2 times the width of the image size.

The bottom of the screen should be at least 40" to 48" (about 1.2 Meters) above the audience floor, allowing those seated in the rear of the audience to see the screen.

This works for all video aspect ratios: 1.77:1 (16:9) / 1.85:1 / 2.1:1 / 2.35:1.

Viewing Angle:
The maximum acceptable viewing angle is 45 degrees. Beyond that characters and image elements become undecipherable. Ideally, all viewers should be seated within 30° of the projection axis, and never more than 45° off axis.

Screen center should be no more than 20° above the eye level of any viewer.

Diagonal Screen Size:
Because the aspect ratio for video is 4:3, the diagonal produced from those numbers turns out to form a perfect integer relationship: 3 - 4 - 5.

For instance: How large is a 100 inch (diagonal) video screen?

Dividing 100 by 5 equals 20. This multiplied by 3 equals the height of the screen = 60 inch.

Multiply the same 20 by 4 and we get the screen width = 80 inch.

How much ANSI Lumen?

ANSI Lumen = needed Lux on Screen (lux) * Screen Area (m2) / Screen Gain

Example: in a room with regular light (board room or conference room) 400 lux are needed on screen, for a dark room 100 lux are needed.
Screen Size: 6m x 4,4m
Screen Gain: 1.3

ANSI Lumen = 400 lux * 6m*4.4m / 1.3
ANSI Lumen = 400 * 6 * 4.4 / 1.3
ANSI Lumen = 8100

Lighting Level Guidelines:
General lighting should be at 50 fc (+/- 10fc). This is an illumination that is adequate to read, 10 fc for overhead projection, 5 fc for slide projection, 2 fc for video data projection.

Rear projection:
To use a mirror for a rear projection, it must be front-surfaced. Regular glass mirrors have their reflective surface at the back of the glass material. Using this kind of mirror will create double pictures, because the in-beam and the out-beam are not parallel. The light has to go through the glass twice and on the first surface a second reflection will occur.

Front-surface mirrors for projections can be glass and foil mirrors.

 

Glass mirrors have a reflectivity of about 90% to 95% and foil mirrors have a reflectivity of about 80% to 85%. The glass mirror is perfectly flat but heavy. It can even bend under its own weight. The foil mirror is much, much lighter, can be angled in any way but has not this perfect surface.

 

See the Toolbox of www.dnp.dk for projector installations with mirrors.

See www.rearpro.com with very useful tips about mirrors and screens.

 

General Luminance and Illuminace: