I have been working on a diy black-screen for a little while now and have made a little progress. I’m not 100% there yet but I’m not far off either. I can see this is an area that is of interest to people so I thought I’d share my results and maybe get some help and advice on the last few challenges.
Here is a link to one of my earlier tests of my diy black screen material. The bottom half of the screen is painted with screen goo high contrast grey. I though this would be more appropriate than white for the early tests as this is a commercial solution for ambient light with a painted screen (well in theory anyway). As I am making the screen for myself, I don’t benefit from making it look good artificially. That would just hurt me.
http://www.youtube.com/watch?v=6-LDZ1LwAVU
The screen in the test is 80 inches. I am not going to make my 120 inch screen until I am done testing but I expanded the image to make sure my results didn’t just look good because the screen was small. I also calibrated the projector for the grey screen (as far as possible) so as not to give the black screen an unfair advantage. The room is brightly lit from 3 directions. A light above with three 100 watt bulbs. A 100 watt side light and the blinds are open on a sunny afternoon directly opposite the screen which is a touch environment for any screen. I think anyone could agree that it is as bright as anyone would realistically expect to watch a movie in. I could move the screen closer to the window to get more sun light on it but that wouldn’t reflect my brightest reality, it would just make the job even harder or be showing off!
You can see in the video that the “high contrast” paint looks anything but in a room that bright. The black screen looked watchable. It wasn’t perfect but encouraging enough to continue the experiment.
In doing my research, I saw that all the high-end screen manufacturers describe their materials as “multi layered”. Not giving much away but it’s a start. It makes sense. A painted screen needs the surface layer to do multiple jobs which are in conflict of each other. Reflect the whole color spectrum, be dark enough to help with contrast and not cause color shifts, smooth enough give a clear image but also diffuse light so you don’t get hot spots. The mixed painted screen is a compromise and leaves you with a fairly light color that has to be neutral. Too dark and you won’t get any image or an image with color shift. Too reflective and smooth and you get hot spots. Separating the layers so that each one can be the best at its job makes sense in theory as long as the let enough light pass to allow you to take advantage of each layer. So as a minimum, I needed 3 layers. A reflective layer, a tinted layer and a light diffusing layer. Think of diffusing as being the difference between a screen and a mirror in terms of the type of reflection.
The screen in the clip has 3 separate layers. The first is aluminum paint for reflection. When dry, I added a separate layer of black paint. When dry, I added a final layer of translucent screen paint. The final appearance was dark grey. Somewhere between the black diamond 0.8 and the 1.4 gain screen (in color only). In reality, it wasn’t grey but had that appearance from the black being visible through the translucent top coat. Normally a screen that dark would not give a good image, not just because it isn’t neutral. A paint that dark as a single layer would be too dim to reflect anything.
The translucent layer is almost transparent when projected on which allows me to take advantage of the black background. Essentially achieving blacks with pigment instead of darkness. On a white screen, the absence of light can only look like a washed out grey with the lights on. With the lights off, the absence of light is black like all the other dark surfaces. With the lights on, black can only be achieved with pigment. This is true even on really bright professional projectors. I have tested with devices up to 8,000 lumens and all look washed out in a bright room with a white screen.
Now, the screen in the clip was an early test and is far from perfect. If you paint on a piece of plexi-glass and hold it to the light, most paints let some light through. The undercoat can have more of an impact than one might think, even with multiple coats. The water based aluminum paint from auto-air recommended for black widow mix is terrible for this. 6 layers and I could still see light shining through it. The exception to this is black paint which seems to kill most light, even if fairly thin. On that screen, I wasn’t able to take advantage of the reflectivity of the aluminum paint so all of the reflection was from the translucent layer. This wasn’t a terrible problem and it worked fairly well. The blacks looked amazing considering how bright the room was and compared to the best efforts of a commercial high contrast paint. For an ambient light screen though, it would be nice to have the option of adding some gain.
The word tint used by screen companies stuck. They don’t use paint in the high end screens for contrast. I think the reason is that tinted film lets light pass so they can use more layers. Many of the tinted window films are designed to allow light to pass without changing color. Some are also designed to not be reflective and to stop glare. All useful properties in this quest.
The other problem is the translucent paint and specifically, my ability to apply an even smooth coat. It isn’t very forgiving. One mistake and you have to start over. Even with the best of rollers, it is also hard to make it really smooth like a pro screen. Using a solid screen printing roller, I got fairly close in the clip. From watching distance, it is smooth enough but not perfect.
TBC
Here is a link to one of my earlier tests of my diy black screen material. The bottom half of the screen is painted with screen goo high contrast grey. I though this would be more appropriate than white for the early tests as this is a commercial solution for ambient light with a painted screen (well in theory anyway). As I am making the screen for myself, I don’t benefit from making it look good artificially. That would just hurt me.
http://www.youtube.com/watch?v=6-LDZ1LwAVU
The screen in the test is 80 inches. I am not going to make my 120 inch screen until I am done testing but I expanded the image to make sure my results didn’t just look good because the screen was small. I also calibrated the projector for the grey screen (as far as possible) so as not to give the black screen an unfair advantage. The room is brightly lit from 3 directions. A light above with three 100 watt bulbs. A 100 watt side light and the blinds are open on a sunny afternoon directly opposite the screen which is a touch environment for any screen. I think anyone could agree that it is as bright as anyone would realistically expect to watch a movie in. I could move the screen closer to the window to get more sun light on it but that wouldn’t reflect my brightest reality, it would just make the job even harder or be showing off!
You can see in the video that the “high contrast” paint looks anything but in a room that bright. The black screen looked watchable. It wasn’t perfect but encouraging enough to continue the experiment.
In doing my research, I saw that all the high-end screen manufacturers describe their materials as “multi layered”. Not giving much away but it’s a start. It makes sense. A painted screen needs the surface layer to do multiple jobs which are in conflict of each other. Reflect the whole color spectrum, be dark enough to help with contrast and not cause color shifts, smooth enough give a clear image but also diffuse light so you don’t get hot spots. The mixed painted screen is a compromise and leaves you with a fairly light color that has to be neutral. Too dark and you won’t get any image or an image with color shift. Too reflective and smooth and you get hot spots. Separating the layers so that each one can be the best at its job makes sense in theory as long as the let enough light pass to allow you to take advantage of each layer. So as a minimum, I needed 3 layers. A reflective layer, a tinted layer and a light diffusing layer. Think of diffusing as being the difference between a screen and a mirror in terms of the type of reflection.
The screen in the clip has 3 separate layers. The first is aluminum paint for reflection. When dry, I added a separate layer of black paint. When dry, I added a final layer of translucent screen paint. The final appearance was dark grey. Somewhere between the black diamond 0.8 and the 1.4 gain screen (in color only). In reality, it wasn’t grey but had that appearance from the black being visible through the translucent top coat. Normally a screen that dark would not give a good image, not just because it isn’t neutral. A paint that dark as a single layer would be too dim to reflect anything.
The translucent layer is almost transparent when projected on which allows me to take advantage of the black background. Essentially achieving blacks with pigment instead of darkness. On a white screen, the absence of light can only look like a washed out grey with the lights on. With the lights off, the absence of light is black like all the other dark surfaces. With the lights on, black can only be achieved with pigment. This is true even on really bright professional projectors. I have tested with devices up to 8,000 lumens and all look washed out in a bright room with a white screen.
Now, the screen in the clip was an early test and is far from perfect. If you paint on a piece of plexi-glass and hold it to the light, most paints let some light through. The undercoat can have more of an impact than one might think, even with multiple coats. The water based aluminum paint from auto-air recommended for black widow mix is terrible for this. 6 layers and I could still see light shining through it. The exception to this is black paint which seems to kill most light, even if fairly thin. On that screen, I wasn’t able to take advantage of the reflectivity of the aluminum paint so all of the reflection was from the translucent layer. This wasn’t a terrible problem and it worked fairly well. The blacks looked amazing considering how bright the room was and compared to the best efforts of a commercial high contrast paint. For an ambient light screen though, it would be nice to have the option of adding some gain.
The word tint used by screen companies stuck. They don’t use paint in the high end screens for contrast. I think the reason is that tinted film lets light pass so they can use more layers. Many of the tinted window films are designed to allow light to pass without changing color. Some are also designed to not be reflective and to stop glare. All useful properties in this quest.
The other problem is the translucent paint and specifically, my ability to apply an even smooth coat. It isn’t very forgiving. One mistake and you have to start over. Even with the best of rollers, it is also hard to make it really smooth like a pro screen. Using a solid screen printing roller, I got fairly close in the clip. From watching distance, it is smooth enough but not perfect.
TBC