Comparison of Stereo Screens

1st Investigation - Screens not Available New

I recently borrowed the new Da-Lite screen (with "Silver Matte" finish) which is 8 feet wide. A quick test during our recent club meeting showed that this screen is not as bright as the older Da-Lite screen (which is using the Wonderlite material). While using this screen it was rather obvious that "ghosting" was worse than usual. So I decided to investigate. I collected 8 screens, measured their brightness and extinction, and documented their texture. The results are summarized below. Some things to note:

1. A good screen is a screen that shows high brightness and high extinction. From these two properties, in my opinion extinction is more important. If the extinction is low then "ghosting" becomes a problem. According to Ferwerda, 6 f-stops is the minimum extinction for a screen to be suitable for stereo.

2. A quick way to compare two screens visually: Put them next to each other, partially overlapping, and turn the projector on (both lamps). Look at them and compare the brightness. Then turn one lamp off, take a piece of polarizing material (viewing glasses are OK), orient the glasses to achieve maximum extinction and compare them again. The darker screen shows the highest extinction.

3. To construct the Table below I have used a digital light meter to measure light intensities. All the values are in f-stops. A difference of one f-stop means twice (or half) the amount of light.

	Screen Type	Texture	Brightness	Extinction
1	Da-Lite VIP 50"		0.5	7.5
2	AMC 50"		-0.2	6.2
3	Montgomery Ward, 40"		0	7.3
4	Knox Panorama, 40"		0	6.5
5	New Da-Lite 96" 8 foot wide made from new material Silver Matte		-0.7	5.4
6	Original Da-Lite 72" This is the traditional Wonderlite material (now discontinued) it belongs to our stereo club.		0	7.2
7	My Da-Lite 72" I bought this after I heard that Da-Lite was discontinuing their Wonderlite material. I did not realize that this was different until now.		-0.4	6.3
8	Da-Lite Silver Lite 40"		0.1	6.7

These results are plotted below:

Summary of Observations:

1. Curiously, the data points follow a trend: Brighter screens also show better (higher) extinction. A good screen must be high in the upper right corner.
   
2. From the 8 screens tested the best screen is no. 1 which is brightest and shows the higher extinction. The worse screen is no. 5 (new Da-Lite Silver Matte material) which shows the least brightness (one f-stop less that a good screen) and the least extinction (two f-stops less than a good screen). This is the only screen that does not meet Ferwerda's minimum 6 f-stops extinction.
   
3. Most screens (1, 2, 3, 8) have a coarse lenticular texture (I measured ridges per inch - the line marker is one inch). The Wonderlite Da-Lite material (Club's screen, 6) shows a less coarse texture (about 44 ridges per inch). "My" Da-Lite screen shows a different pattern, similar to the Knox Panorama screen (4). Finally, the new Da-Lite screen shows a very different texture, the least intense than any other screen. Clearly, texture is a factor in the performance of a screen, but not the only factor because screens with apparently similar textures can have different characteristics (compare screens 1 and 2).

Conclusion: It is best to avoid the new Da-Lite screen even though the 8 feet width is very attractive. "My screen" (7) was made after the Wonderlite material ran out. It is not as good as the Wonderlite but still better than the Silver Matte. It appears that Da-Lite is moving in the wrong direction. Perhaps we should put some pressure to improve their material? Reel 3-D (www.reel3d.com) has 72" screens in stock and I am told that they are as good as the original Da-Lite Wonderlite material.

George Themelis

DrT-3d@att.net

Updated: November 2002