Hi all, I’ve just been doing some tests for the second DI table I’m building at the mo. For the first table, our team discovered late into the project that rosco blocks a lot of infra red (although others have had more success than I did with rosco). This led us to look for a quick solution to our problem of what we could use for a projection surface that would sustain a decent image but not block infra red. We came across purlfrost white, which is basically an adhesive film used to privacy windows etc. It’s manufacturers state that it lets over 70% of light through while also being much more opaque than standard frosted effect stickers. We found that using purlfrost allowed us to get good blobs and a fairly good projection image also. However, we found that our table suffered from ‘hover’ quite a bit and also, when projecting white or light colours, the glare from the projector bulb was just a little uncomfortable if you looked right at it.  The projected image would also have benefited from being brighter (so basically the purlfrost was too transparent). So this time round I thought I’d buy a little extra purlfrost and do some comparison tests with two layers of film. The results are below.

In the first pic the double frosting is on the left. The pic might not do it justice but it was clear that the image looked better on that half of the acrylic.

The second picture is taken from behind the acrylic, with the camera facing the projector beam. This was mainly to see if the amount of glare was reduced, which I think you’ll agree it is.

So I think that in terms of projection quality then two layers of purlfrost are the way forward.

But I thought I’d do some further tests to make sure that it didn’t mess up the infra red.

The first image is taken with both hands on the acrylic, one on each side (obviously). The double frosted side (on the right) blocks more infra red but I believe this is a good thing as in the next photo you can see an image taken with oth my hands around an inch away from the surface of the acrylic. While both sides show hover, the double frosting side is much better.

So in conclusion, I will be putting two layers of purlfrost on the next box!

I hope this proves useful to someone, I post it here because purlfrost is cheaper than rosco, easier to apply and will work better with DI. A lot of people are making boxes on a budget and this is an easy way to save some cash!

I would also like to point out that in order to press ‘print screen’ while keeping my hands on the acrylic I had to stand on one leg and press the button with my big toe! Yes I probably did look like an idiot

Here is a link to purlfrost website http://www.purlfrost.com/purlfrost.php

EDIT the ‘second’ pic mentioned above which shows the image when pointing at the projector is now the last image displayed as I initially uploaded the wrong file…

I didn’t get to read your whole post, but I wanted to let you know you’re using the wrong filters in your touchlib set. You’re using filters set for FTIR. You need filters for the DI. You’ll see drastically better results when using the right filters. If you’re not sure how add the right filters search the forum as there’s tons of information. You need to edit your config.xml and take out brightnesscontrast, and add simplehighpass, and scaler from the rear-di example xml file.

Thanks cerupcat, I should have mentioned that I knew I wasn’t using the right filters. The test was purely to see how the purlfrost worked when doubled. Since the filters were the same for both the left and right side of the acrylic I believe the results should still be valid.

Thanks for the heads up though!

BTW loking forward to the new tracker Cerupcat

There is one iussue that using this kind of material normally will case big hot spot from projector, and I can see it from ur pic. :D

Maybe you mean it will cause a bright spot, which I agree it does and is the reason why I tried two layers. No infrared hotspots though, that was one area our last box didn’t have any issues. I think that depends more on the projector itself.