Any projector will do, but the brightness you get is very important. Apparent brightness is determined largely by three things:
- The Lumen output of the projector. The calculation for the ideal minimum amount of Projector Lumens needed.
- The Reflectivity (or gain) of the projection surface. Every type of screen / surface has a different percentage of the light that will be reflected back at the audience. A typical 'matte white' screen in a classroom is about a 1.0 gain. Bed sheets are about 0.9 gain. Screens from Stewart, Draper, DaLite, Rosco, Rose Brand all have published gain numbers you can use. Higher gain screens (1.5 to 2.5+) tend to have a narrower viewing angle, so it depends where the screen is situated relative to the seats whether or not this matters. Some High Contrast screens have a gain between 0.5 and 0.8 (they appear grayish to the naked eye).
- The Size of the image greatly affects the net image brightness. If you double the screen dimensions (say go from a 4' x 3' 'classroom' screen up to an 8' x 6' screen (assuming the same material and projector), then you will need to project 4X the amount of Lumens to get the same effective image brightness. Double that again to 16' x 12', and you will need 16X the Lumens. You can see that a 1,000 Lumen classroom projector rapidly needs to be upgraded to a 16,000 Lumen device as the screen size increases.
So, what is the goal you are shooting for? Experience has shown that a screen brightness of about 20-30 Lumens per Square Foot MINIMUM is needed in an auditorium (this is NOT a Movie Theatre where all the lights are off and the side walls and ceiling are dark matte finishes - this type of controlled environment only requires about 12-16 Lumens per Square Foot).
WARNING: MATH COMING! A Great STEAM moment!
Projector Lumens needed to get to your goal:
Projector Lumens = (Desired Screen Lumens per Sq. Ft.) x (Screen Width in feet) x (Screen Height in feet) / (Screen Gain)
Example: 5400 Lumens = 30 x 16' x 9' / 0.8
For a Cyc-sized Screen: 21,600 Lumens = 30 x 32' x 18' / 0.8
Contrast Ratio: Hold up a white sheet of paper - this is about the same gain as a bed sheet. You will notice a distinct white color to it (amazing!). Guess what? This is what BLACK will look like. You can't project Black, you can only project more white (or colors). Higher gain screens tend to reflect back more of the ambient light in the room (or set), which in-turn washes-out the image. This is why TV sets / computer displays look so nice - they have a very dark appearance when there is no image on them. Rear Projection can work to your advantage if you use a screen material that is designed for that purpose because it has a low-reflective front face and the dark space behind the screen (really important - DARK BLACK space behind the screen) makes the blacks truer. Frosted Shower Curtains do not do this very well - they still look light gray from the front. There are also front projection screen materials that have a low gain / high-contrast surface that are engineered to reject ambient light from overhead or the side, and these can help with a front projection in a room with some ambient light.
Carefully cropping (shuttering) any stage or house lights so they do not spill light onto your projection surfaces can help a lot.
Stacking projectors to double-up or triple-up the brightness can work, but you need to be very diligent about how the projectors are mounted so they don't cook each other from the heat they produce, are secure from movement, and so they can be independently micro-adjusted so the pixels line-up on top of each-other. Two 4,000 Lumen projectors effectively create an 8,000 Lumen projector, and three can effectively create a 12,000 Lumen projector.
Image Blending is when you place multiple projectors spaced apart and each one delivers a part of the total image with a little bit of overlap. Special software (sometimes built into the projector) assists the user to align the overlap zones and 'blend' the images together. This can create a big image using multiple smaller (less powerful) projectors, and can be helpful when there is a limitation as to how far away from the screen the projector can be located (say, limited back stage space in a rear projection set-up). Blended images can be across one or two image axis. Example: 1x3 (horizontal), 3x1 (vertical), 3x3 (both)
Lens selection is important as each projector / lens combination has a limit as to how large or small you can make the image, and within what range of distances from the projector to the screen you can actually get the image to focus. Small cheap projectors don't typically have interchangeable lenses, larger 'industrial' / 'professional' projectors typically accommodate a large variety of lenses that can be rented and allow the projector to be situated in a more convenient location while still filling the screen with an image.
Placing projectors in the audience seating area, or above the audience seating area, can introduce a lot of stray light and fan noise that may be distracting to the audience.
- Projectors on tables in the seating area blow hot air on the audience seated near them, and must be very secure so they don't get knocked-over and damaged. Cable must be routed very carefully and securely so that they don't present a trip hazard. ADA recommendations are that bumps (discontinuities) in the walking surface should be no more than 1/2" (AND CLEARLY MARKED), so big fat SO power cables and big bundles of signal cables must be avoided.
- Projectors mounted overhead must be mounted with brackets specifically engineered for the product. Plywood shelves, rope, ty-wraps, and other home-made rigging are NOT acceptable. 10-100 pound projectors can cause severe injuries and financial losses should they fall. Do it right or don't do it at all.
'No image' or a 'blank screen' doesn't mean you are projecting 'nothing'. Most projectors have fairly low internal contrast ratios, so even when you feed BLACK to the projector, you still get GRAY on the screen. Turning-off the projector, then turning it back on again is stressful for the projector electronics and the lamp(s), and the start-up image produced by the device may not always be predictable or controllable. It is better to turn-on your projectors before the audience enters the room, and leave them running until the last bright lighting cue after they are no longer needed.
- Installing a hard shutter in front of the projector lens is the only way to get BLACK or nothing to be cast upon your screens. There are remotely operated 'dousers' that achieve this function that can be purchased or rented. If your prop shop is skilled, they can also make a little remote control arm that moves a shutter (Rosco Black Wrap) in front of the projector's lens. This makes a good tech project!
Wiring: VGA signals, even with really large good cables, are limited as to how far you can go before the image gets soft and fuzzy, or even fails to work. Similarly, HDMI cable have a limitation, too. This can create problems when you are trying to put your computer at the back of the seating area and your projector is on or near the stage. You will probably need a cable extender that utilizes CAT5 (or better Cat5e, Cat6a) type computer network cables as the transport medium. There are several different protocols used, most of which are not actually ethernet network compatible, so DO NOT connect the cables through the schools network jacks unless you know for sure that you won't destroy any equipment. Using signal extenders are for a point-to-point connection utilizing data type cables, not the building network (unless you have a Video Over IP solution). One of the most common extension systems today uses a signal format call HDBaseT. This typically accepts a signal from a HDMI source (or from a DVI-D or DisplayPort device via an adapter). At the projector there is another interface box that converts the signal back to HDMI, DVI, or DisplayPort. Some of the newest projectors have HDBaseT connections built in, so you only need the signal converter at the sending end. There are also fiber-optic based signal extenders that work very well over large distances.
Wireless: Some projectors have MiraCast or Apple AirPlay receivers built-in, or you can use an outboard adapter to send the signal to the projector (distances are limited). There are numerous 'xxxCast' variations out there (Extron, Crestron, Barco, Christi, and many more), and intercompatibility is almost non-existent, so test and re-test to get this technology to work for you.
I know this all sounds expensive, but the good news is that you can rent all of this gear, you don't have to buy it.
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Erich Friend
Theatre Consultant
Teqniqal Systems
Original Message:
Sent: 08-04-2016 10:58
From: Michelle Meyer
Subject: Projections
I would like to use projections in my upcoming production of Laramie Project. I am not sure how to do this. My idea is to have two large screens on either side of the stage and use them for the television reporters and the hospital updates. I was looking at projecting from the back but I need help with logistics. What kind of fabric for the screens and can I use regular projectors? Do I need a special computer program?
Thanks
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Michelle Meyer
Frederick MD
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