:: Screen Technical Info - Projector Screens Direct

Screen Technical Info

How important is contrast? Contrast is also key to a good image and has been the holy grail of home theatre for decades. High contrast is difference between the whitest whites and the blackest blacks on screen. The more shades between white and black, the better the image, the better the colours and the better the shadow detail. That is exactly why the cinema is dark, to keep the blacks black. Any ambient light will wash out the image and ruin contrast. Some companies promote grey screens for home cinema. The year is 2009, the contrast ratios of projectors in this day and age is more than sufficient. We do not need grey screens at all. If you are planning on using a projector in an environment where ambient light is an problem, dont go grey. The bad far outweighs the good.

How important are black borders and surrounds on your viewing surface? A nice jet black velvet surround is the ultimate finish to any fixed projection screen. The advantage of fixed screens is you can have a rich, jet black velour frame that yields a brighter, crisper and more colour saturated image. The blacker the borders the more intense the picture is going to appear. See below for contrast illusions. The main advantage of a Black Velour frames is to both soak up overscan and create a crisp edge to your image. Have a look below at a comparison between a powder coated frame and a velour frame. No matter how accurate you project the image onto the screen, with a powder coat frame there will always be annoying reflections coming off the frame. Using jet black velvet like Fidelio Velvet assures zero reflections and a beautifully masked image. Using a velour frame not only adds a touch of class to your screen it also ensures that the projected image appears how it was meant to be with no distractions. At night time your screen should dissapear when it's being used.

Note the grey boxes on the right side of figure 1 appear to be lighter than those on the right hand side. You may be surprised to see the grey boxes are indeed all the same colour. This is a prime example of how much brighter your picture will appear with a black velour frame surround. It may an illusion but it works well. We do not recommend coloured frames, especially timber style frames with fancy edging. If the frame does not have black velour masking on the inner edge consider it a badly flawed design. Always insist on a black velour frame finish.

Fidelio Velvet Frames for the blackest frame surround possible. This stunning true Velvet is exclusive to Oz Theatre Screens. It truly makes other frames look grey by comparison.

Sharper edges for your image Not such a massive problem with blu ray and hd dvds but for standard definition dvds you will find the edges of the image very soft and blurry. This is another reason black velour is used. The idea here is to actually overscan the image approx 8 to 10mm on all edges to take away the soft edge of the image. The difference is simply astounding.

Our black Fidelio velvet is the blackest velvet available worldwide! Overscanning has a real purpose. See the cropped images below. The top image (scope film) has no velour on it's bottom edge, you can see the grey bars being projected onto the screen and you can see the soft edge. The image under this has a nice crisp and sharp edge because the slightest amount of over scanning was done to remove the blurred edge. These are real screen shots but we have needed to, in this instance, add the black edge in on the bottom image as this is just not possible to capture on a computer monitor. If you live within driving distance please feel free to arrange a private viewing, we can show you this in person. You will not want a gap between the edge of the image and the frame anyway, so by nature you will project some light onto the frame.

Here are two real time screen shots of our black velour VS a matte black painted wall. We shifted the lens off the left side of the screen and took two shots with the DVD on pause. The left shot is without the flash, the right shot with a flash, we then turned up the brightness on the right hand shot so you can see the difference. This of course is not required if you see this in person, the matte black painted wall clearly shows the image without the flash. Our black velour is the best light absorbing velour on the market, hands down. This product is something very unique to Oz Theatre Screens. (Please note this is our OLD velour, not Fidelio velvet which is MUCH blacker again) Will update again with new photos when time permits.

With and without flash side by side.

GAIN, DIFFUSION and REFLECTION:

"A screen surface has a gain of 2.4 and a 180 degree viewing angle". This is scientifically impossible. You cannot cheat the physics.
The apparent brightness of a high gain screen simply must drop off when you get further away from the centre. (off axis) It cannot reflect back more light than is being projected onto it. Even the best reflective surfaces absorb a small percentage of the light that falls onto the surface.

Today there is a very strong movement away from high gain screens. Which, in fact were first developed for low powered projectors - 400 ANSI lumens or less. Todays projectors are in excess of 1000 Lumens, some less, which is fine too. In short, high gain screens are just not necessary in home theatre.

It is all about how the light is diffused and reflected. A screen surface cannot reflect back more than 100% of the light hitting it. It cannot create light. All a high gain screen can do is directionally reflect the light back in a certain direction, however, high gain screens are either retro reflective, which reflects the light back to the light source (the projector) or reflective which reflects the light back in the opposite direction in the same way that a mirror reflects light. This is how the best reflective projection vinyls work including Evolution3D.

There is no possible way for a screen to have a gain of over 1.2 and have a 180 viewing angle with the brightness staying even the further you move away from the centre of the screen. There are screen fabrics out there today claiming to have a gain of 1.6 and 160 degree viewing angle, with 'special' optical coatings making the screen 60% brighter. You just cannot achieve this. They may have a 160 degree viewing angle but the image will look something like the the 2nd image below.

More importantly is the need for OPAQUE fabrics. This means a fabric that prevents light from travelling through the screen. If you look around you will see screens that are wafer thin single layer pvc materials. The projected light travels right through these fabrics ruining the PQ and reducing your image brightness and contrast from anywhere upto 40%. Always ask if the fabric is opaque and has a backing to prevent light penetration. All of Oz Theatre Screens fabrics are opaque.

Have a good look at these image changes below (2nd photo on right). You can see why high gain fabrics are not suitable for home theatre. This is what can happen during a movie when using a high gain screen (including glass beaded screens).

What is GAIN?

When shopping around for a home theatre screen you will hear the terms "high gain" and "low gain" Gain is the measuremnt of light that is reflected off the screen surface. It's referece to which all screen fabrics are measured against is magnesium oxide (plaster) which has a gain of 1.0 and is a diffuse surface. In other words, a gain of 1.0 means there is no gain at all, it will diffuse
light only and does not have any reflective properties. So if a screen vinyl has a gain of 1.2 means this means the screen reflects 20% more light (back to the viewer) than a standard pure white magnesium oxide board under the same conditions.

There are only three ways that screen material can reflect light:

RETRO REFLECTIVE - Reflects the projected light back to the source (avoid)

DIFFUSIVE - Reflects the projected light with almost complete diffusion. This means when the light hits the screen it diffuses the light equally all over the screen, resulting in the widest viewing angles of 180 degrees.

REFLECTIVE - Reflects the projected light in the opposite direction to the source. If the projector is floor mounted the light is reflected back toward the ceiling, (not where most people sit, right ?)

However if your projector is ceiling mounted this is, by far, the best type of surface providing the gain is not over 1.3. Anything over 1.3 will have a tendancy to hot spot. 1.2 to 1.3 is the 'sweet spot' for home theatre projectors.

Results and recommendations: Mattte White: This is the preferred surface for the home theatre, use only a matte white fabric with a gain between 1.1 and 1.3. A 1.1 to 1.3 gain fabric will give you a universal viewing angle (or extremely close to it) and more accurate color rendition. Evolution3D has a 1.26 gain.

What to avoid When shopping around for a screen for home theatre, be sure to avoid any screen with a gain greater than 1.4 unless it is used for REAR projection only, (rear projection screens are non opaque so the light cannot hot spot) High gain screens also tend to have beaded or textured surfaces which can be easily damaged, making cleaning a nightmare.

The Smoother the fabric the better!

Be very wary of the textured fabrics being offered on 99% of motorised and pull down screens. This is old data screen material is rampant in Asia because it's cheap to manufacture. The market here in Australia has been flooded with these cheap imports. You simply cannot acheive image accuracy with this cheap outdated data screen fabric. In fact it's so bad you would be better off using a white wall! See these photos below to learn why.

Left side image: This is the fabric texture we are talking about. This is the nastiest screen fabric you can use, hands down. Certain auction sellers will tell you it's 1080P certified or optically correct, nothing could be further from the truth. The actual texture will be visible when watching movies on the screen. Not what the projector manufacturer intended you to look at. AVOID THIS FABRIC TYPE AT ALL COSTS If you want an accurate picture from your home theatre projector.

Right side image:

Here we have a correct image from our premium fabric Evolution3D. The image is reflected back to the viewer exactly how the projector manufacturer intended. No hot spots, no texture, nothing but a clean and accurate image with strict white field uniformity and accurate spectral response.

So always insist on a sample of the fabric, even an A4 size swatch will give you a great idea of how it's going to perform.

Remember, the screen fabric is the thing you will spend most of your time looking at.

SCREEN FABRICS

A good quality screen fabric should:

1. Produce true and accurate colors
2. Allow the projector to display it's full resolution with no screen textures visible
3. Give the widest viewing angles - both horizontal and vertical
4. A screen that does NOT hot spot

In other words, a good projection fabric should allow you to see the limits of the projectors ability. Evolution3D on the right hand side VS a standard single layer pvc substrate. The difference is astounding when compared side by side.

Evolution3D is Australia's first projection vinyl designed specifically for the new crop of 1080P Projectors. Designed with an optically enhanced 1.26 gain front surface which is dead smooth, the fabric itself dissapears allowing both 1080P and even 4K projectors to shine with vivid colour and accurate image fidelity. Any HD Projector will greatly benefit from Evolution3D - Oz
Theatre Screen's premium fabric.

We do NOT use rigid board as a screen surface. Rigid screens can, over time cause the frame to skew out of shape. They also cost a fortune to ship and a hassle to move as you cannot take them apart. Vinyl has been used for over 80 years for projection screens, it enables optics to be mixed into the cast when the product starts off in it's liquid form. (PVC is an oil derivitive, like everything these days!)

Rigid screen use coatings which deteriorate over time which of course deteriorates your image! Their optical coatings can also rub off which makes cleaning a nightmare. Think about it this way. A good optically cast vinyl has it's optics IN the actual product whereas coated surfaces have their optics sitting on top which leaves the product vulnerable to the deterioration mentioned
above. NOTE: Some vinyls are also optically coated. Evolution3D is optically cast - Highly recommended!

The 4 main types of projection fabric we offer are;

• Evolution 3D - matte white - fully backed - Thickness 380 microns - gain 1.25 - front projection - spool 2.1 metres - Suited to 2K and 4K resolutions.
• Optema - grey tint -rear projection - Thickness 220 microns - gain 1.4 - rear projection - spool 2.4 metres
• Acoustic Vision - NEW Moir'e free acoustically transparent fabric - Thickness 400 microns - gain 1.16 - front projection - spool 2.44 metres.

• Acoustic Vision4K - NEW - Moir'e free acoustically transparent fabric - Thickness 400 microns - gain 1.16 - front projection - spool 2.44 - Suitable for both 2K and 4K resolutions.

The are a number of reasons that Matte white low gain screens are the best materials to use in a 'Home Theatre' environment.

The main advantages of using a 1.1 to 1.4 gain matte white screen surface

• Low gain screens give a universal viewing angle - this means that no matter where you sit the picture will be equally bright & clear, giving you more seats in your home theatre.

• Low Gain screens don't hot spot because the light is diffused evenly from edge to edge. High gain screens tend to hotspot because the they cannot diffuse the light evenly.

• High gain screens are too bright in the centre of the screen and the light reflection falls off quite dramatically as you go further away from the centre.
• Low Gain screens are matte white, this gives a colour neutral reproduction, so all of your movies look natural and life like. Where as high gain screens can have a number of problems when used in home theatre. You can have color shifts in both the blue and red spectrum (hue).

CHOOSING THE RIGHT SCREEN SIZE:

You will normally know your seating position from the screen before anything else.

Both THX and SMPTE recommend seating to be no closer than 2X image height. For a 100 inch screen which is 1243 high, this would mean 2.48 metres from the screen. This is the CLOSEST one should sit.

3X image height being the recommened seating distance from your screen. In order to resolve 1080P properly.

4X image height should be seen as the maximum seating position from your screen.

We generally work on a formula of between 2.5 and 3.5 times image height, this narrows down the correct screen size for your seating position.

You want your 'relaxed eye' to hit the middle of the screen. The height of your screen will vary according to the seats you use.

SCREEN FORMATS: We offer many different size screens and formats for both front and rear projection. 16:9 HDTV and Cinemascope are the 2 most popular choices because HDTV is in 16:9 and movies transferred to DVD are usually in Cinemascope format with those dreaded black bars top and bottom. See our Cinemascope page for more info. By using an Anamorphic lens and a Majestic Scope screen you can now enjoy Deluxe Widescreen in your own home with no black bars top and bottom - The way the Director intended.

How much bigger is a Projection Screen over a TV?

Just for fun, here's some information on 'why a projector and screen is the best value choice. Plasma TV vs Projector and screen. It takes 6.2 X 42 inch plasma TV panels to fill a 100 inch 16:9 projection screen. See photo below. (to scale) Or 4 X 50 inch Plasmas to fill the same screen.