Home Theater Forum and Systems banner

1 - 7 of 7 Posts

·
Registered
Joined
·
3 Posts
Discussion Starter #1
I have been reading your website with keen interest. I am based in Dublin, Ireland with access to UK DIY stores such as Homebase and Woodies. I have built a dedicated 12 seat cinema with dims of c. 16ft (4.8m) x 26ft (8m). The room is all dark shades with no ambient light and is dedicated to movie viewing.
I have a JVC HD100 illuminating an imaginary screen 12ft (3.6m) wide x approx. 6.75ft (2.05m) high. This equates to a diagonal size of about 165" which is asking a lot of the c.700 lumens the pj puts out. The pj is on a special stand which is 23ft (7m) from the screen and exactly centred on it.The actual screen size (white painted area) is 12ft x 5ft to give a 2.4 - 1 configuration.
For me, the cimema experience is all about immersion. I like to be immersed in both the picture and the sound and am happiest sitting 12ft away from the 12ft wide screen. Effectively, I have blacked out the top and bottom of the 16 - 9 image projected by the jvc. I have black gates either side of the screen which I can use to reduce the screen width to a 16 - 9 configuration and adjust the zoom on the jvc to correspond if I wish to. I hope that this all makes some sense and thank you for staying with me this far.
In order to test my ideas about the wide screen I simply painted the screen with matt white/black emulsion on the plastered wall. This worked so well that I put off buying a screen. I am very intered in the idea that I might be able to improve my "screen" by using one of your paint mixtures or a variation that I might easily acquire in this part of the world. Great website. Best regards. Bryan
 

·
Moderator Emeritus
Joined
·
3,772 Posts
Hi Bryan,

Welcome to HTS!

Thanks for the kind words.

Since you have a dedicated home theater with dark interiors and no ambient light problems, a white screen would probably serve you best. The only reason to go to a gray screen, even as light a gray as Cream&Sugar, is to gain image contrast due to either ambient light or a projector that needs help with black-levels. With your PJ only producing about 5 fL. at your screen it sounds like a matte white screen would be the best DIY solution for the widest viewing angle. Depending on your seating arrangement you might be able to add a bit of sheen by going to the next level above matte, but it doesn't take much extra sheen to cause hot-spotting so it's a gamble.
 

·
Registered
Joined
·
3 Posts
Discussion Starter #3
Thank you, Harpmaker, for responding so quickly. I had always anticipated requiring a screen with a gain of at least 1.5 to make the most of the projector. I did not feel that I knew enough about screens at the time to make the right choice, hence the temporary white paint. I guess that the "brilliant white matt paint" has a gain of about 1.0 or slightly less. Can I achieve a gain of 1.5 through a paint mixture or is there a better way with the setup that I have? I would be most appreciative of any advice that anyone can give me in this regard as there is obviously a huge level of expertise associated with this website. Best regards. Bryan
 

·
Moderator Emeritus
Joined
·
3,772 Posts
Screen gain is a topic that is easily misunderstood, please read the Sticky thread on that topic; Bill does a great job explaining it. The main thing to remember is that the higher the screen gain the smaller the viewing cone will be because the reason the screen is brighter when viewing head-on (seats in the middle of the theater) is that it is dimmer when viewing at an angle (seats close to a side wall). The screen takes light from the periphery of the screen to make the center brighter.

We have only just begun to measure screen gain ourselves (actually mech does it), but we haven't measured any DIY screen mix yet with a gain of much over 1.0 that doesn't show hot-spotting.

The two primary ways to increase a screen mixes gain is to increase the surface sheen or to add a reflective agent to the paint. It doesn't take too much added sheen to make the screen hot-spot and I haven't experimented with this yet.

There are a number of "shiny" things that can be added to paint, the easiest to find are "metallic" paints that contain coated mica flakes instead of real metal. The problem is that all of the mica-based paints I have tried have a prismatic effect to them (it's how mica works, it refracts as well as reflects) and break up light into rainbows or shift colors. I think this is controllable to a degree by keeping the amount of mica-based paint in a mix below a certain percentage, but I haven't looked into this in any great detail as yet. The screen mixes I have tried from other forums that use mica-based paints have hot-spotted for me.

The two mixes that I have the most experience with are Black Widow and Cream&Sugar. BW uses aluminum paint as the reflective agent and C&S uses a rather unique paint only available in North America (but the search continues for a substitute). I don't know what the reflective flakes are in Craft Smart Metallic Silver. From their physical properties they aren't aluminum and they aren't mica. Both aluminum and CSMS are gray by nature (the paints are just the flakes in a clear acrylic medium) and so they will darken any paint they are put in. At only 5 fL. at your screen I'm guessing you can't go with any darker shade.

I am almost clueless when it comes to commercial screens. Bill and mech are the guys with experience there, and I don't think they will be around here until next week sometime.
 

·
Registered
Joined
·
184 Posts
hello Bryan,
sorry for not jumping in earlier.

my advice is to try absolute white in dulux lumitec light and space rich matt. it seems to have slightly more sheen than regular white paint and has been reported to have a gain of 1.3 on a uk forum from what i recall. actually it has been used by many in the UK to good effect including myself.
 

·
Registered
Joined
·
3 Posts
Discussion Starter #6
Thank you both for your helpful responses, I am guessing that "hop-spotting" is where there is a direct reflection of the pj lens? (you might add this to your glossary). This would be a problem for me as my pj is centred on the screen. I had anticipated the "viewing cone" so all seating is within 30degrees of the centre-line. I will try to get the dulux paint and try it on part of the screen. I will let you know the results. Many thanks, Bryan
 

·
Moderator Emeritus
Joined
·
3,772 Posts
You are welcome, although I don't think I helped you much. I forgot about the paint Custy told you about. It is definitely worth a try. If I remember right it is extremely close to being a neutral white (most white paints are actually a very, very light orange with some leaning more to yellow and others to red).

The developers here are trying to get some samples of different reflective agents to make lighter paint mixes than is possible with aluminum, but unless one is willing to buy in 25 Kilo barrels they don't want to talk to you. The search continues.

I pulled this image from the thread http://www.hometheatershack.com/for...screens/5977-gain-other-confusing-topics.html and it shows what hot-spotting generaly looks like if it's centered on the screen.



I'm pretty sure this is a photoshopped recreation and not an actual screen photo, but you get the idea. In real life, hot-spotting can show up in various places on the screen depending on your viewing angle to the screen in relation to the PJ.
 
1 - 7 of 7 Posts
Top