[geeks] paint that retains polarisation?

[Francois Dion]

On Fri, Sep 26, 2008 at 12:34 PM, Dan Sikorski <me at dansikorski.com> wrote:
> Rick Hamell wrote:
>>
>> Francois Dion wrote:
>>>
>>> Is there paint I can buy at home depot / lowes / whatever that has
>>> high retention of light polarization? I know of Krylon aluminium
>>> paint, but I'd like to find something I can paint with a roller and
>>> that dont look out of place on a wall.
>>>
>>> I know about the paint from those fancy "home theater specialists"
>>> places, but I am not paying $400 for 1 gallon.
>>
>> http://www.goosystems.com/index.php?cont=home is "the" paint to use, but
>> it's the $500/gallon area for top coat, and $129 gallon for bottom coat.
>>
>> You might try finding one of those retractable projector screens. It seems
>> to me I use to see fairly large ones in the ~$100 range at used office
>> equipment stores. We used to play Halo on XBox this way and it worked pretty
>> well.
>>
>> I did a bit of looking, but I can't figure out what is in the paint to
>> make it more friendly to a projector. It looks like it just needs to reflect
>> light, so a semi-gloss or gloss might be fine?
>>
> I don't think that's quite it.  If you've ever used a projector on a
> whiteboard that isn't intended for that purpose, you see the reflection of
> the projector's bulb/lens on the makeshift screen.  I think a gloss surface
> is too reflective, semi-gloss might be ok.
>
> This would also be pretty sensitive to how it is applied.  With a normal
> roller or brush you get a texture that would not be ideal for a screen.
>  However, the OP didn't indicate that this is the actual application here,
> so we might be making a bad assumption.

It is for projection on a wall. Currently I have no problem with 2D movies.

I put up the wall myself, insulated and finished with densearmor plus
sheetrock (did wonders for the sound). I did a grade 5+ job on the
joints. Semi gloss is too reflective for my projector (1400 lumens)
even with gray color so I ended up with eggshell. Base coat was the
best primer that Home Depot had for application on drywall. Then I
applied a few coats of Behr Silverscreen (upw base) in eggshell
applied with a foam roller (gave me the best result). Surface is not
100% perfect, I should have applied plaster to the whole wall and then
machine + hand sand the whole surface, but I wanted to watch movies in
this millenium, not the next... At any rate, I only (and I'm the only
one that notices) get a slight hotspotting in very specific instances
/ movies, such as Sahara (the desert scenes just light up that wall
and you'll see any and all defects).

But back to my original question. I'm looking to retain as much of the
light polarization as possible. Why? For 3D.

I have a mirror splitter/combiner in front of the projector, using 4
mirrors, and in front of that, a pair of linear polarizing filters.
One at 45, the other at 135 degree. I have the matching 45/135 glasses
with a metal frame, aviator style, same type of polarization as IMAX
theather. This is different than the Real D system which uses circular
polarization, but it is the same concept.

I feed the projector from my HTPC, with mplayer displaying the movie
in an over/under setup, so my mirror setup is vertical. The external
mirrors are aligned so that the two images are superimposed. Up to
now, all is good. But the paint on the wall doesn't retain enough of
the polarization and it is ghosting way too much.

Francois