Behind the Scene: Rear vs. Front Projection
Rear projection used to be the holy grail of projection. The idea is that by putting the projector behind the screen, in its own room or space where ambient light hitting the back of the screen can be contained and controlled, you can achieve the best image. This also helps to make the image more resilient to ambient light that may be hitting the front of the screen.
One of my main issues with rear projection is that by using rear projection screen material, you reflect a lot of the brightness back toward the projector. This results in a significant loss of brightness, which means you'll have to spend more money for a projector that can provide even higher brightness than the image brightness you need. Another concern is the space required behind the screen for the projector to throw the correct size image.
Of course, front projection comes with its own set of problems. First, you traditionally have to hang the projector from the ceiling somewhere out in the room, which can be unsightly. And, of course, ambient light can wash out the image on your screen. One workaround for the first issue—an obtrusive installation—can be solved with the selection of a long zoom lens that allows you to put the projector at the back of the room. However, these lenses are quite expensive, which only adds to the cost.
So which approach is the right one for your space? The answer, not surprisingly is: it depends. There really isn't one solution that is right for every space and budget. However, there are some ways you can quickly determine which option might be best suited for your application.
If you're ready to tackle the front vs. rear debate for your job, here are the key questions to answer:
- Where would be the best place in the room for a screen or screens? Depending on the answer, there may not be enough space or room behind the screen to place a projector, which will automatically dictate a front projection solution.
- How much ambient light do you have in your room and how much control do you have over it? If you cannot control the amount of ambient light, you will need to look at a combination of a higher-power front projector (with a higher lumen rating) and an ALR (ambient light-rejecting) screen. These materials reject ambient light that does not come from the same axis as the projector and can actually help increase your dynamic range (the difference between white and black). This does mean more cost, but it will still allow a front-projection install that may be a simpler and less expensive solution than rear-projection once you factor in potential construction-related expenses. And it will certainly come in below the cost of a large-format TV or LED video wall.
- Will you be displaying mostly text or video and images? If you are going to be displaying a lot of text, a front-projected image will give you a slight edge in fine detail compared to a rear-projected image, though this gap has closed significantly in the last few years as screen materials have improved.
Rear Projection Pros & Cons
Rear projection can take quite a bit of valuable space away from the facility; a room must be dedicated for the use, and that means a loss of classroom and/or storage space. In older facilities stretched on space to begin with, that can be a serious concern.
As mentioned, the throw distance can also be a challenge, even when there exists what seems like a reasonable space to dedicate to the installation. Fortunately, there are some very clever systems that have been developed to help alleviate the sometimes shocking throw distance requirements for rear projection. These complex systems use one or more mirrors to bounce the image around in order to achieve the necessary distance for a given screen size. However, this introduces more potential points of failure, as even a small shift in one of these mirrors can result in a need to re-calibrate the entire system.
Rear projection screen materials can cost more money than front projection screens, as well. The technology employed by rear projection screens can cost more in research and development and manufacturers must recoup those costs, usually in the form of a higher price tag.
Nonetheless, for those of you who have facilities that can accommodate a rear projection setup, it is definitely worth looking into, especially for situations that require a high value placed on aesthetics and hiding as much of the technology as possible.
Along those lines, another situation where rear projection could prove useful is where noise levels may be an issue. Projector fans, especially on high brightness projectors, are not usually the quietest, and places like museums, theaters, and churches can benefit from reduced ambient noise levels by hiding the projectors away in another room.
Ultimately, then, it comes down to what your facility will allow. Do I think having rear projection is worth the cost of remodeling your facility to accommodate it? Not usually. I would say that 95 percent of the time, you can achieve similar, if not superior, results with front projection for the same, if not less, investment.
One reason for that is the wide range of ALR screens now available. With the multiple options currently on the market and the plethora of low cost, bright, high resolution projectors that have also emerged, there's typically very little reason anymore to look seriously at rear projection. Does that mean it's not a viable solution? No, but it will not produce a significantly better image than a front projection system that incorporates a properly matched projector and screen combination.
Still, if you are in a situation where having front projection is simply not an option, for whatever reason, then rear projection is a possible alternative, and probably a better option than investing in an LED video wall or large format televisions. As I stated earlier, there is no magic equipment package that is right for every situation, and this is why it is so important to work with a consultant or system integrator who can help steer you toward a good decision that will serve your needs for years to come. When you choose the right components that work well together, your projection investment can last for much longer than you thought possible.
Tim Adams is president and chief systems designer for Timato Systems, an audio/video integration company specializing in servicing the sound, lighting, video, projection and live-streaming needs of churches and other houses of worship. He can be reached at firstname.lastname@example.org.