There are various factors most know about when setting up a projection system but the proverbial “devil in the details” often goes overlooked. I’m talking about a projector’s vertical alignment. It is a relatively simple function but it has small elements to it that every installer should be aware of and that goes double for houses of worship. It may be a small matter but the difference between doing it right and wrong will come with either great rewards or a potentially costly disappointment. This is especially important with Churches because there are so many different ways a projection system can be installed and often, there are more variables at play than an enclosed conference room or home theater. As a person of faith, I want to contribute to your congregation’s success and this is one of those AV veteran moments where a small bit of advice can spare you from buying expensive AV gear you don’t need while getting the best performance out of the equipment you have (or can realistically afford). This is also a topic that will help enhance you the ability to make wise decisions when buying AV gear whenever an upgrade or new building project is in order. With all that said, saddle up; for the next few minutes we’ve got work to do….but it’s AV stuff… so it really just going to be fun anyway, right?
Keep in mind that calculating the wrong projection angle can create a multitude of problems for you.
This article also serves to aid you in selecting your projection screen so that any alignment issues due to product incompatibility can be avoided. Factors such as , projector type, atmospheric lighting and screen material that all come into play. Since your screen complements your projector, here are some basic rules regarding how to choose the right projector and screen combination.
On a projector, there is typically a feature known as vertical lens shift. This is the projector’s ability to shift an image upward or downward from a projector’s static position without need of physically moving the projector itself. Depending on whether you are ceiling-mounting your projector to shoot down on a screen from the front, or “table-top” positioning from in front or behind the screen, will determine the degree of “vertical adjustment” required from your projector. For high ceilings, a projector with up to 3-times the screen height is required. For in-line imaging typically from a table top or low ceiling installation, a projector that can only adjust up to ½ the screen height may likely be the ideal solution.
*Tip, there are times when you will be able to actually tilt the screen itself to accommodate the projection angle you have. This is often practiced with the angular-reflective “ALR” screen materials.
ALR, Angular Reflective
ALR, Retro Reflective
CLR, Ceiling Light Rejecting (aka. “ST” or “UST” material)
Whatever your requirements are, always make sure that the desired “sweet spot” of optimal projector screen performance will encompass your entire viewing audience. Ambient light rejecting screens are great but they may not be as ideally suited to your large venue presentation as a white screen would be. Either way, always have a good handle on what your projector’s vertical angle is and what angle of projection your screen can handle. If you do it right, you’ll appreciate the results, your congregation will be grateful for a beautiful display and the cost of all this enjoyment should be less than what you may have expected.
About the Author:
Dave Rodgers is a guest writer for numerous publications and the Marketing Manager for Elite Screens Inc., with 20-years experience in the AV and wireless communications industries. He travels worldwide playing an active role with international business development and is regularly consulted in matters of branding and new business development. David has made numerous television, radio and editorial appearances providing installers and Do-It-Yourselfers with easy solutions toward creating larger-than-life big screen applications.
*See the illustration above for instructions on how to properly calculate projection angles if needed.
When adjusting your projection angle, think in triangular terms. There are 3-points of measurement used in the formula. They are the physical spacing between the projector and center of the screen (A); the height difference between the screen’s center and the projector lens (O); and the calculated throw distance from the lens to the center of the screen (H).
Here is How to Calculate in Geometric terms:
Formula for Hypotenuse (H): √(A² + O²) = H
(Use a Scientific Calculator)
Step 1. Measure the distance of A & O (either metric or imperial) Per the illustrated example above, A= 240” & O= 36” √(240² + 36²) = H
Step 2. Square both numbers √(57600 + 1296) = H
Step 3. Add both numbers √(58896) = H
Step 4. Get the square root and round no lower than the nearest hundredth √ of 58896 ≈ 242.68”
Your measurement of H is 242.7 inches distance between the actual lens and the screen’s center.
Step 5. Calculate the triangle’s Asine by dividing the height (O) by the diagonal (H) 36/242.7 ≈ 0.148
Step 6. Use the “2nd “ or “Inverse” function on your calculator and press (sin-1) and…
Your estimated angle will be 8.5 degrees
What you learned from this calculation is that your angle of projection will be appropriate for either a matte white or angular-reflective material but not appropriate for a retro-reflective material