Darkgray Munsell N2.5-3.5 screen for daylight viewing - Page 2 - Home Theater Forum and Systems - HomeTheaterShack.com

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post #11 of 15 Old 09-20-10, 05:24 AM Thread Starter
Join Date: Jul 2010
Location: Germany
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Re: Darkgray Munsell N2.5-3.5 screen for daylight viewing

Just an update on my as 'dark as possible screen'.

After reading some posts in 'the other forum' on the extruded aluminum material boschrexroth and 8020 sell I decided to built my frame with this material
and using gray spandex as screen material.

I'm using two 20x20 profiles with a length of 2360mm and two 20x20 with a length of 1370mm. Those will be connected with 4 of the 2way cube connectors.

I added 70mm on each side of the 102'' screen frame because I'm working on a DIY spandex blackscreen for daylight viewing and need those 70mm for 'integrated' masking purposes.

The cube connectors were ordered because i didn't want any sharp corners and there is no need for 45 angles with those.

I'll use several layers of 4-way spandex and mylar, which will be stretched over the frame and connected in the rear of the frame with black plastic tubes.

In case I run into problems fixating the spandex in the corners I'll screw thin steel washers on the cubes rear and use superstrong neodym magnets (15mmx3mm, 2.3kg pull) to solve that problem.

The complete screen will only have a weight of about 4-5kg.

I got a whole bunch of different gray spandex samples (many are very small though) and tried to find the best 'as dark as possible' (for Acer H5360 aka emachines v700 PJ) material.

Several problems showed up when reaching a gray level of approximatly Munsell N5 or less.

a) the darker the gray gets the more 'blueish' the image gets, especially skin tones suffer. It seems like the gray 'eats red' the most.

b) for getting a decent white level the glossy side of a N6 or darker spandex must be used.

c) backing the gray spandex with white or black spandex has decreasing influence the darker the gray gets.

d) Silvermetallic spandex as backing doesn't have an evenly reflective surface when stretched and isn't more efficient than a simple white backing. It also has got a sparkling issue. When using it's rear with a slightly yellowish n7 graytone it works nicely, but has sparkling problems in very bright scenes.

e) a thin see through gray spandex with about N8 backed with a black spandex is behaving almost like a N5 gray spandex. The problem with it is it doesn't have enough gloss to produce a good white and must be stretched very evenly .

I got some Mylar to see if it improves the gain more than a white backing without producing further problems.

It seems like Mylar increases the 'gain' of the used gray spandex aproximatly by 1-2 levels on the Munsell scale. I E a N3.5 gray has whites like a n5. I couldn't test it on a large scale yet, but have ordered graphit gray (N3.5) spandex and the thin see through N8 gray spandex in case I run into problems with the Mylar directly backing the graphit gray spandex.

Also in case the N3.5 backed with mylar doesn't work as expected I still will have a nicely working screen when using the see through n8 and backing it with the N3.5 spandex.

It seems like anything darker as N5-4 is too dark for 2000 lumen in eco mode PJs, even when using the glossy side of the material, if it's not backed by mylar. Maybe it would work with 3000-4000 lumen PJs...

Best regards!

Last edited by Darker_plz; 09-20-10 at 05:50 AM.
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post #12 of 15 Old 09-20-10, 09:42 AM
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Re: Darkgray Munsell N2.5-3.5 screen for daylight viewing

Darker_plz wrote: View Post
a) the darker the gray gets the more 'blueish' the image gets, especially skin tones suffer. It seems like the gray 'eats red' the most.
It's not that it 'eats red', it pushes blue more. The problem with going darker is as things move closer to black there are more pigments used and darker ones and this has an impact on the image.

For the most part what we 'see' as black is actually a deep dark purple. The darker you go the harder the blue push. If you were to have a neutral gray, even as dark as N2.5, you wouldn't see any push. The image would of course still be dimmer because more light energy is being absorbed but it would still be color accurate.

For something this dark you would either need a very bright projector or a lot of gain, and both have their drawbacks. The brighter the projectors is typically the lower the contrast is. If you find a bright projector with exceptional contrast be prepared to pay premium dollars for it!

Gain also has its negatives. I see so many people talk about gain as if it is something magical. Not only does gain affect the viewing cone, if the gain is too high it also can start causing color shifting to happen. Granted I don't think that's what's happening here, I just wanted to point that out is all.

Fabrics use different pigments than paints and they typically use inks and dyes. Black ink really isn't black at all. As mentioned it's actually a dark purple. The dyes are the same and black isn't black. That's why when you have a pair of black jeans or pants they start to get that purplish look after they have been washed too many times.

If you had a bright enough projector you could blast through all this and still get acceptable whites, but again as mentioned, typically the contrast is lower.

Just wanted to give you some food for thought as to what's going on

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post #13 of 15 Old 09-20-10, 04:46 PM
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Re: Darkgray Munsell N2.5-3.5 screen for daylight viewing

Thanks for the update Darker_plz. We have not tried using Spandex as a screen material primarily due to all the problems you are discovering and the fact that you can't control the color of the screen yourself (as you can with a painted surface). The performance of the material is greatly affected by how it is mounted and how much it is stretched. When you start layering different colors and sheens of material things get even more complicated and begin to climb toward the point where it becomes difficult for others to duplicate one's working screen.

A Spandex screen is still an item of interest, especially to those wanting to make a acoustically transparent screen.
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post #14 of 15 Old 09-23-10, 12:19 PM Thread Starter
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Re: Darkgray Munsell N2.5-3.5 screen for daylight viewing

The 'DIY Blackscreen' is finished. It needs a little bit more stretching, but I'll do that in a few days when I got a helper (did the inital stretching myself) and the spandex is hung out. I had to increase PJs brightness, contrast and red a bit, and decrease blue and green a little.

Apart from the above already mentioned boschrexroth material I used:
-2 mylar rescue blankets (the silver side facing to the front)
-Black plastic tubing ( pieces of about 15-20 cm)
-Graphit gray spandex with about N3.5 http://www.stoffkontor.eu/bekleidung...-grau/a-12492/
-see through spandex with about N8 ( http://www.stoffkontor.eu/bekleidung...allic/a-12227/)

Here's the making of...

The glossy side of this material was used

The frame corners look like this

Connecting the material to the frame

The infamous flash picture of the screen (ignore the messy wall, it will be repainted soon...)

a few pictures of the viewing cone (not very sharp,but that's my error not the screens)

full daylight and ambient light

Another sample of full daylight and in darkness

and another sample of ambient light vs darkened room

I'm happy with the results. There are some things I would do different next time:
-try to get a mylar sheet the correct size or use 2 equally sized mylar rescue blankets pieces.
-stretch the mylar first and connect it to the outside T-slots, then stretch the spandex and connect it to the rear T-slots

Things to watch out, when rebuilding it:
-get several samples of the spandex material from different shops, test them and use the most neutral one you can find.
-The see through material is very important, without it you'll get a problem with the mylar backing creating hotpots and sparkles.

Best regards!

Because of the lines you can see on the flash picture of the screen, I didn't just restretch it, but also turned the dark gray spandex around so the glossy side is facing to the rear now. That's much better. Before you were able to see the lines on the glossy side in very bright scenes like explosions etc. Now the screen works even better than before and even has a bit more contrast.

Last edited by Darker_plz; 09-29-10 at 11:46 AM.
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post #15 of 15 Old 10-26-10, 01:58 PM Thread Starter
Join Date: Jul 2010
Location: Germany
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Re: Darkgray Munsell N2.5-3.5 screen for daylight viewing

Just wanted to keep you updated.

After having watched all sorts of movies on my screen I'm still very happy with it.

Here are some things I enjoy most about my dark gray screen:
-No masking needed. 16:9, 4:3 or any other format just looks great. There's almost no difference noticable in the gray tones of the movieborders to the material not lighted up by the pj.

-Ambient light no problem. Even with the lamps on theres a very viewable image. No need for a bat cave. Dimmed lighting makes almost no difference to total darkness.

-It is 'cat safe'. As often as my cat has climbed the screen any pvc screen material would have been shredded. The claw marks in the spandex are gone within hours. (Trying my best to convince my cat not to climb the screen...)

Best regards!
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darkgray , daylight , munsell , n2.5-3.5 , screen , viewing

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