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What type of projector screen should you get?

If your budget is tight you could always use the wall

by Steve Withers Aug 5, 2015 at 3:59 PM


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    What type of projector screen should you get?
    One of the great advantages of a projector over a TV is that it can deliver a really big image without taking up much space at all.
    In fact you could even start with a small budget projector that you just get out when you want to watch something and project the image onto a white wall. As long as the wall is matte white and smooth it will make a perfectly good screen and will be a cheap way of initially getting into projectors, allowing you to add a screen later. Whilst a white wall is an option, a decent screen will certainly help get the best out of your projector and possibly even address some of the limitations of the projector or the room itself.

    In our previous article we took you through the various different types of light sources used in modern projectors. In this article we'll take you through all different types of projector screens available, we'll explain screen gain and discuss the different types of screen material you can buy. We'll also explain why you might want a different aspect ratio for your screen, as well as go through anamorphic lenses, zoom and shift, side masking and acoustically transparent screens.

    Type of Screen

    First of all you can either get a screen that comes down when you need it or one that is permanently fixed to the wall. If you get a screen that can be rolled up when you don't need it then make sure it is reasonably rigid when pulled down, as any undulations in the surface can be quite obvious depending on the content. You can either buy a screen you manually pull down or a motorised screen and there are models designed to keep the screen material taut, although they can be quite expensive.

    Assuming no one else in the household minds a projector screen being permanently on the wall, you can get a fixed screen instead. This type of screen is always designed to be very taut, thus eliminating any unevenness in the surface and you can get surprisingly good results without spending a lot of money. Ultimately the overall price will be dictated by which manufacturer you choose, how large you want the screen, the aspect ratio and the actual material used. If you want to hide your speakers behind the screen surface, for that genuine cinema experience, this will also add expense and some image problems with the material and the weave or holes used to let the sound through. See the section below for more details.

    Screen Gain

    When it comes to the actual screen material itself, the most important factor to consider is the gain. The gain is a measurement of the reflectivity of any screen or projection surface. The gain number represents a ratio of the light that is reflected from the screen as compared to the light reflected from a standard white (magnesium oxide) board. The higher the gain of a screen, the more reflective it is. So a screen with a gain of 1.0 will reflect the same amount of light as a white board, whilst a screen with a gain of 1.5 will reflect 50% more light. Alternatively a grey screen with a gain of 0.8 will reflect 80% of the light from a white board.

    The screen gain that is best for you will very much depend on the type of room you have and the brightness of your projector. If your room is very dark, then you should choose a material with a 1.0 gain because this will diffuse light evenly across the screen. If your room isn't dark but your projector isn't very bright, a higher gain screen may help. However if you have a bright projector but a room with light coloured walls and ceilings, a lower gain screen (grey) can help reduce reflection reflections and improved the perceived blacks and contrast ratio.

    It might sound counter-intuitive to buy a grey screen but they can be very effective in the right circumstances. What you mustn't assume is that a high gain screen is preferable to a lower gain screen. Like most things in life there's a trade off and the higher the gain the less effective the viewing angles on the screen and the more likely you are to get hot spots (where the middle of the screen appears brighter than the edges). A higher gain screen can also suffer from the surface sparkling if viewed in a pitch black room, so in that kind of environment a screen with a gain of less than 1.3 and ideally 1.0 is preferable.

    Ambient Light Rejection Screens

    In recent years screen manufacturers have taken the viewing angles of different gain screens and used it to their advantage. The idea is to create a screen that rejects ambient light when seen from a certain angle. This type of screen uses a multi-layer optical surface that only reflects back the light from the projector and reflects away light coming from other angles such as ambient light from walls, ceilings, floors or windows. The result is a projected image that can retain its blacks, brightness and contrast ratio even in less than ideal rooms, although the optimal viewing angles can be restricted. These ambient light rejection screens are highly effective but they are very expensive and clearly they have their limitations; even the best ambient light rejection screens couldn't handled a room flooded with sunlight. The easiest way to optimise your projected image is still to just make the room darker but if that really isn't an option then lower gain screens and ambient light rejection screens are certainly credible solutions.

    Screen Size

    In terms of size, this will largely be determined by the size of your room and the throw ratio of your projector. You obviously will need a wall big enough to fit the size of screen that you would like and you will need to make sure that your room is long enough for the projector to actually project an image that large. Simply put, the further away a projector is from a wall, the bigger the image it can project. All manufacturers include throw ratios that show the distances from the screen and the sizes of image that a projector can produce, so check this before deciding on your combination of screen and projector.

    If you want a large screen but have limited space, you could consider a projector that uses a short throw lens, this allows it to produce a big image over a short distance. However you need to be aware of the best viewing distances for an image because if you're sat too close to the screen you might start to see the pixel structure. As a general rule you need to sit at least 1.6 times the diagonal width of the screen; so for a screen that measures 200cm diagonally you would need to be at least 320cm away. You can find out more about viewing distances in this article.
    A negative gain screen can be an effective way of improving the perceived blacks in less than ideal rooms.

    Aspect Ratio

    Another factor to consider is the aspect ratio of the screen because films are usually made in one of two ratios - 1.85:1 or 2.35:1. The majority of new TV programmes are made in a ratio of 1.78:1 so, depending on what you watch, a screen with a 1.78:1 ratio would be ideal for almost all TV viewing and any 1.85:1 ratio movies. When you watch a 2.35:1 ratio movie on a 1.78:1 screen, there are black bars at the top and bottom. If however you watch a lot of 2.35:1 movies, you could get a screen with a 2.35:1 ratio and then watch all your content within this frame. So 2.35:1 films will fill the whole screen, whilst 1.85:1, 1.78:1 and 1.33:1 content will sit within the 2.35:1 aspect ratio with black bars of differing sizes down the sides. At the cinema wide screen films are projected at 2.35:1 but often transferred to Blu-ray in a 2.40:1 aspect ratio; the difference is minimal but that's why you can also buy 2.40:1 aspect ratio screens. Some older films were shot in extremely wide aspect ratios up to 2.76:1, so even on a 2.35 or 2.40:1 screen there will still be slight black bars at the top and bottom if you're watching one of these films in its original aspect ratio.

    Anamorphic Lenses

    If you do decide to get a 2.35:1 screen there are two ways that you can fill the screen with an image. The first is to use an anamorphic lens which allows you to unstretch an anamorphically stretched image to match the 2.35:1 aspect ratio. This approach uses the entire panel of your projector for the image, maximising the resolution of the widescreen projected image and maintaining the brightness. However this approach is becoming less common partly due to the fact that it requires video processing to stretch the image initially, which can introduce artefacts, and partly because the lens itself can cause aberrations. The better the lens the less the aberrations but high quality lenses are also very expensive, which is another reason why anamorphic lenses have fallen out of favour.

    Zoom and Shift

    These days it is far more common to use 'zoom and shift' which means you literally zoom, shift and refocus the projected image to suit the screen. You can either do this manually or using motorised lens controls but the idea is that if you were watching a 1.85:1 movie on a 2.35:1 screen, you would then zoom the image out to fill the entire screen if you wanted to watch a 2.35:1 movie. These days many projectors with motorised lens controls also include a lens memory feature that can memorise settings (zoom, shift and focus) for different screen aspect ratios and then go from one to another at the touch of a button. Using 'zoom and shift' is a lot cheaper than an anamorphic lens, doesn't require scaling and doesn't introduce aberrations but it can reduce the brightness of your image, depending on how large an image you are zooming up to. The approach has become so popular that even commercial cinemas use 'zoom and shift' these days.
    If you want to really recreate the cinema experience how about a 2.35:1 screen with side masking.

    Side Masking

    If you do decide to use a 2.35:1 aspect ratio screen you can also use side masking to reshape the screen to different aspect ratios within the 2.35:1 ratio. The reason behind this is that a black border makes the image appear more defined and brighter, so even if you don't get side masking make sure your screen has a black border around it. You could make a manual form of side masking that you move in and out depending on the aspect ratio of the content you are watching, be it 1.85:1, 1.78:1, 1.66:1 or 1.33:1. Alternatively you can buy motorised side masking that will automatically move in or out depending on the aspect ratio you choose. This approach really adds to the feeling of being at the cinema but of course, it's not cheap. If you have a 1.85:1 screen, you can also get masking that comes down from above and up from below to frame a 2.35:1 film with a 1.85:1 aspect ratio screen.

    Acoustically Transparent Screens

    One problem that people often encounter when installing a big projection screen is where to put the front three speakers (left, centre and right). The obvious solution is to put the left and right speakers either side of the screen and the centre speaker beneath it. However this isn't ideal for a number of reasons. First of all if you're using a 2.35:1 screen the left and right speakers may be too far apart. If the centre speaker is below the screen, near the floor, you might lose the sense that dialogue is emanating from the screen. Finally from the perspective of creating a cohesive from sound stage, you really want to use three identical speakers that are all at the same level.

    The solution to this problem is to use an acoustically transparent screen because then you can position the centre speaker or even all three speakers behind the screen. This is exactly what is done in a commercial cinema and can result in a very effective installation because all you see is the image and not the speakers. An acoustically transparent screen has tiny holes that allows the sound through whilst still delivering a detailed picture. When using an acoustically transparent screen you need to make sure the holes are smaller than the pixels that make up the projected image or you'll get moire patterns. For this reason there are acoustically transparent screens made especially for Ultra HD 4K projectors.

    As long as the acoustically transparent screen is well made it shouldn't affect the audio and is effectively like having a grille in front of the drivers. For this reason when position speakers behind an acoustically transparent screen, you need to remove the speaker's own grilles. In terms of setup you have two options, you can install the speakers into the walls and then mount the screen on the wall, or you can mount the screen away from the wall and position the speakers between the screen and the wall. Whichever approach you choose, the sounds and especially dialogue will now be emanating directly from the screen, really adding the cinema-like experience.

    What Next?

    As you can probably tell, when it comes to your choice of projector screen the options are extensive and can quickly get very expensive. So the first thing you need to do is establish what your budget is and then decide which type of screen best suits you based upon your projector, your needs and the room itself. Now that we've established which projector to buy and what type of screen you need to get, in our next article we'll give you some simple tips on how to get the best from your new projector and screen.

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