OK this is a little off the topic of film projection, but it is something that is annoying me trying to pick out a video projector, and a new slide machine for my church.

Slide and film projector brightness is usually measured in terms of their bulb wattage, which is highly inaccurate of course. LCD projectors are usually measured in lumens, which is pretty accurate, but foot-lamberts really gives an indication of how bright the screen is.

Now here's the question: I have a 350 watt Kodak slide projector, and a 16mm B&H with a 300 watt bulb. These projectors are throwing up an 8ft diagonal picture from a distance of 65 feet in a 200 seat sanctuary. Both of these projectors are a little dim getting ambient light from 5 windows down each side of the building during the day, but are fine at night.
Our new building will seat 650 in theater-style. Ambient light will be from 2 small curtained windows per side, and some aisle lights. The throw distance will be 80 feet, and will be making a 20 ft diagonal picture. It is my job to pick out an LCD projector that will illuminate the screen bright enough with just enough ambient light to tell whose sitting beside you from the windows, and the aisle lights.

For NTSC video (not 16:9 HDTV), a 20-foot diagonal means you have a screen area of 12X16=192 square feet.

If you use a new matte white screen with a gain of near 1.0, you would need at least 16X192=3072 lumens to get 16 footlamberts.

If your auditorium is long and narrow, so the audience is not seated more than about 15 degrees from the perpendicular centerline of the screen, you should use a gain screen to reflect more image light to the audience, and pick up less of the ambient light. For example, a screen with a gain of 1.8 would reduce your light output requirement to 3072/1.8=1920 lumens. If you have a wide auditorium, a gain screen would have to be curved to maintain adequate luminance uniformity when viewed from the side seats.

Take video projector specs with "a grain of salt" --- factor in that the light output may be overstated and based on ideal operating conditions and maintenance. Light output typically will decline with lamp age, misalignment, variations in input voltage, etc.

Since you are likely buying a new projector and new screen, you should involve a theatre equipment dealer or professional AV specialist/dealer in helping choose appropriate equipment that will meet SMPTE specifications.

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John Pytlak, Senior Technical Specialist
Worldwide Technical Services, Professional Motion Imaging
Research Labs, Building 69, Room 7419
Eastman Kodak Company
Rochester, NY 14650-1922 USA
Tel: 716-477-5325 Fax: 716-722-7243

1,000 lumens is like a slide projector with a 300 watt bulb. Lumens are rated on a logrithmic scale. So when a manufacture tells you that his 1,200 lumen projector is better than somebody else's 1,000 lumen projector, he is hyping it up. The only way you would be able to tell the difference, is if someone brought in a 2,000 lumen machine.

I had good success with the Sharp XG-E3500U 1,300 lumens, which costs between $7,500 and $10,000. This is a robust projector. Eike is a Sanyo usually sold for cheaper. They have a great 1,900 lumen machine for a little cheaper than the Sharp. The Sharp has the best video section I have seen.

Contact your local Audio Video Rental house and see if they have any used projectors you could buy. Make them come to your church for a demo and make a spair lamp part of the deal.

The throw distance of the standard lens that will come with the machine is between 1.5:1 and 2:1. It is difficult and expensive to change lenses on an LCD video projector. It can be done, but trust me, if you can make it work with the standard lens, you will be much happier. On an 8-foot screen that comes to between 12 and 16 feet. Sometimes a mirror can be used in a rear projection situation but it sucks 30% of the light.

A front projection screen is bad in a high ambient light environment. The screen reflects all light, windows, projectors, light bulbs and the magnificence of God. In theatre lobbies I always used Rear Projection. If it is darker behind the screen or can be made darker, try that. Again the AV Rental house could rent you a rear projection screen to try.

e-mail me directly and I can give you more indepth advice.

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