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Fool On The Hill » Blog Archive » How to Pick a Projector

These formulas are used as a standard for general acceptability by many talented media specialists. I didn’t make them up, but rather did research and gathered them from other smarter people. One of these smart people is Anthony Coppedge. A lot of this information was taken from materials that he made publicly available on the Church Media Network Forums. I understand that he has since published them elsewhere. Quite the opposite of being subjective these calculations can give you some actual hard numbers to base your decisions on. They are hardly comprehensive, but again the goal is to help us mere media folk gain a footing. There are many unscrupulous or unknowledgeable sales people who will recommend anything just to make money. Personally I am skeptical about advice coming from someone who has a vested interest in the outcome. The ideal situation IMHO is to hire a consultant that doesn’t sell anything, unfortunately this is far beyond the means of most churches.

These calculations are *very* basic as stated and merely a starting point. There are many other factors that can come into play.

Lenses are very complex (a good lens can cost thousands). Screens are also a more complex subject (some actually magnify light in the center) Contrast ratio makes a huge difference in perceived brightness. Viewing angles need to be considered. A good scaler will increase the brightness as well. The decision to use either front or rear projection is a big one.

A good consultant will take everything into consideration. The problem is that most smaller (poorer) churches never consider all of the other factors. I often hear in the forums – just buy the best you can afford. This can be very poor stewardship on several levels – you can over spend, buying more than is needed or waste money by underspending on an inadequate system. These formulas can at least help you figure out what ballpark you are in.

Finally these numbers are hardly written in stone. There is plenty of wiggle room as far as what is acceptable. Some will decide that even the best isn’t good enough and some will be satisfied with much less if that’s all that can be afforded. It’s always nice to have some hard numbers to present to those in authority in situations where someone wants to donate something that won’t meet your needs.

Question: Do these numbers take into account the degradation of projector lamps over their lifetime?

Answer: Good question, but no they don’t take into account bulb dimming. The brightness numbers (lumens) are basically what has been determined to be legible/acceptable to most people. This is what I’d consider ideal viewing conditions. Many people (when money is involved) are willing to settle for less than ideal in terms of screen height and brightness. So with bulbs aging and growing dimmer – you start out ideal and replace when it’s unacceptable. You could also over specify (a bit) and do the same thing. This would give you a longer period of acceptable brightness. The dimming is pretty gradual and what’s acceptable is very subjective.

How to determine Projector Specifications:
(how many lumens do I need)

Rather than just buy the biggest/best/brightest you can afford……..

I’d humbly suggest doing your homework first. You may need some help, but you can actually calculate how big of a screen you need and how bright of a projector you need. It’s simple math that leaves little to guesswork. A good consultant or a local sales rep worth his salt will do these calculations and measurements for you. It’s worth understanding the principles even if you don’t want to DIY.

Here are the basic formulas:

First determine the screen size (height actually):
Measure the distance from the screen to the furthest seat in line-of-sight. If the majority of the content is video, divide that number (the distance) by 8. This will yield the screen height. It’s important to note that the aspect ratio doesn’t matter.

Next, measure the distance from the screen to the closest audience seat that is in line-of-sight to that screen. The screen should be no taller than twice that distance. Example – 6′ tall = 12′ away for closest viewer. This isn’t always possible, but it is preferable. Remember, the furthest viewers take priority, as it is better for the screen to be “too big” for those close than “too small” for those in the back.

For Example
:
80’ / 8 = 10’ screen height for the furthest viewers
20’ / 2 = 10’ screen height for the closest viewers

The screen height will be the same if the aspect ratio is 4:3 or 16:9 as only the width is different (if done correctly, anyway). This is not the same as “letterboxing” a 4:3 image, so make sure you’re either using 4:3 or 16:9 – not letterbox.

Next determining the correct lens:
The projector to screen distance doesn’t effect the brightness of your image!
Let that sink in a bit. Your lens collates the light and doesn’t allow it to spread out and diminish as your high school physics would have you believe. You may need a lens with a different focal length, depending on your distances. These lenses can have a big impact on image brightness, but not the distance. A faster (brighter) lens will always cost more. The good news is that the lens you need can be easily determined, just keep in mind that a really fast, long focal length lens may cost more than the projector!

Using Ratios to Select the Correct LCD Lens:
When using ratios to select a lens, you must consider the screen width and the projection distance to the screen. The formula is distance/width. For example, our screen is 8′ wide and if we projected from a distance of 8′, we would require a lens with a 1:1 ratio (or a zoom that covers this range). Our actual distance is 21′, you would then require a lens with a 2.6:1 ratio. However, due to the different LCD panel sizes, the actual focal length of the required lens would be different for each panel size, even though the ratio would remain the same. If you can determine the size of your LCD panels you can get the info you need from THIS CHART. Also note that the speed of a lens may change over it’s focal length.

Determine how bright a projector (lumens) you will need:
Determine square footage of the screen surface –
Take the screen height (in feet) and multiply it by the screen width (in feet).
For example (assuming 4:3). 6′ x 8′ = 48 sq. ft.

Multiply the square footage of the screen by 20 (ANSI says 18 + or – 2, so we use 20).
Example – 20 (ANSI lumens per sq. ft. minimum) multiplied by 48 (sq. ft.) = 960 projected lumens.

960 lumens isn’t hard to find in a projector by today’s standards. But before you get too excited, remember that ANSI specifies that 18 (+ or – 2) is the acceptable number. This is assuming NO light is hitting the screen. Pitch black area. Dark. No light. Nada.

Our next measurement is at the screen area itself – the amount of foot-candles of light striking the screen surface from lights, windows, etcetera. You will need a good light meter to determine this.

Let’s say you measured 16 foot-candles striking the screen surface. We now take our number (16) and multiply it by 5 (our next formula).
16 x 5 = 80

That (80) is the number we must now reach to have adequate lumens being projected onto the screen surface. In other words, we must project at least 80 lumens per square foot onto the screen to overcome 16 foot candles of light on a 6’ x 8’ screen.

In your case we have 48 sq. ft. of screen area. We multiply 48 by the new 80 lumens per sq. ft. number to get 3840 lumens.

Therefore, assuming no screen gain (some screens can collate light into the center like a lens), we will need nearly 4,000 lumens projected onto the screen surface from the projector in order to overcome ambient light.

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