DIY Projector Guide - Part 3 - Enjoying your Projector

From Lumenlab

Results

Spirited Away with Scott

Fractal madness.

Projection Screens

Discussions and opinions on screen types and materials are abundant and hotly debated. The bottom line is; a flat-white, smooth wall is for all intents and purposes a nearly perfect screen. Screen materials can have various properties to enhance the picture, namely ‘gain’, contrast and color correction. A very light grey screen can improve contrast in low contrast projections, the trade off is a lower gain screen. Gain is a screen’s ability to increase reflectivity in the line of viewing. Of course no screen can reflect more light than the projector can make, but it can reflect that light directly back at the viewer rather than diffusing it as a flat white surface will. The disadvantage to this is a lessened viewing angle and ‘hot spots’. Gain in usually increased by adding a silvery surface or glass bead to the screen material. Many have made high gain screens themselves by experimenting with various silver paints or gesso combinations. Older lcd panels have what is called ‘green push’, meaning they have a slight green tint to the picture. Adding a bit of yellow to the screen material can compensate for this. These types of screens shouldn’t be necessary if you are using a quality lcd panel and good lighting in your projector. Halogen lamps are bad for video projectors because the light is yellow rather than white. Flourescent bulbs can’t make enough light and aren’t point light sources. Metal halide lamps are capable of high output and very white colors and are the lamp of choice for video projectors. Use of proper lighting and quality lcd panels should negate the need for a fancy or expensive screen. (Screens can cost many thousands of dollars.)

If you’re interested in a fabric screen there are many options available to you. The material used for movie screens is available from sources online, but it is quite expensive usually and the benefit isn’t tremendous over a common material called ‘blackout cloth’. Blackout cloth is a heavy material used behind drapes to block incoming light. It is a white or light grey rubberized fabric. It has a cloth side and a very smooth flat white side that makes an excellent screen material. Blackout cloth comes in various widths and is readily available at fabric stores for about $6-$7/yard. The fabric store may have several types so look for the whitest possible, but you may want to obtain a sample of very light grey to experiment with. While you’re there you may find some silvery materials that may make a good screen. Try to obtain samples of these and temporarily mount them on your wall or blackout cloth screen so that you can observe the various effects of different screen materials.

Adding a flat black border to your screen can greatly enhance viewing as it tends to minimize off screen distractions. Black felt works well and is available at fabric stores. If you are using a painted wall you can simply paint a flat black border around your screen area, but felt looks a bit better. Using a black border can be challenging if you use your projector for mostly 16:9 wide screen movie presentations; when you switch to a 4:3 aspect ratio your black border will be in the picture. My set up is geared toward wide screen presentations so I occasionally have problems when I need to project a 4:3 presentation. You could have 2 screens, one for each type of presentation, or you could have a screen that rolls up and down depending on the type of presentation you are projecting. Or you could simply have a large 4:3 screen that you use for both types of presentation, but the results won’t be as good a a black bordered 16:9 screen. If you use a fabric screen you can build a light wooden frame for it or you can get fancy and buy/build a ‘tubular motor’ which would allow your screen to roll up and down at the push of a button.

Important Consideration: Ever notice how dark it is in a movie theater? This is to keep incidental light from reflecting off the screen which would wash out the picture. It is a consequence of forward projection that the screen will reflect ambient light. That said, it is very important for you to use your projector in the darkest possible room for best results. If you have daylight leaking around your blinds it will wash out your projection. Light that is behind the screen isn’t so much of a problem but it distracts your attention. This is important to consider when building your home theater. Many people put their home theaters in their basement because it is the darkest room in the house.