[simpits-tech] rear projection screens

[Steve Wilson]

Yes, do!  I wouldn't want it for flight sim, but the thought of having an 8'
mirror for a telescope is intoxicating.

Steve

----- Original Message -----
From: "Rob Hommel" <rhommel at tacoma.net>
To: "Simulator Cockpit tech list" <simpits-tech at simpits.org>
Sent: Saturday, December 20, 2003 9:57 PM
Subject: Re: [simpits-tech] rear projection screens


> Hey Rick:
>
> This sounds worthy of a complete write up for a Simpits article. Teach us
> all how to do this it is something many of us have thought about doing. At
> least I know that I have.
>
> Keep 'em Flying
> Rob Hommel
> ----- Original Message -----
> From: <RickInNoCal at aol.com>
> To: <simpits-tech at simpits.org>
> Sent: Saturday, December 20, 2003 11:56 AM
> Subject: Re: [simpits-tech] rear projection screens
>
>
> > In a message dated 12/20/03 8:58:20 AM Pacific Standard Time,
> > hangr18 at hotmail.com writes:
> >
> > > I'd LOVE to do a setup like this someday, but building a giant
> > > curved mirror is gonna be a bitch....
> > >
> >
> >        Well, actually, no, not really. The mirror needs to be curved in
> two
> > dimensions, not just one, which actually makes it easier.
> >
> >        To make, for example, an 8' diameter curved mirror, make a 8'
> diameter
> > wooden disk out of a couple of sheets of plywood, with a lip about 6"
high
> > all round the edge. Paint the inside thoroughly with epoxy paint to make
> it
> > airtight.
> >
> >        Drill a hole in the lip at some point and epoxy in a piece of
> plastic
> > tubing. Cover the top of this dish you've made with a thin sheet of
shiny
> > mylar - the stuff they make helium balloons out of - pulled as tight and
> wrinkle
> > free as you can get it, and carefully glued all the way round. Then just
> use a
> > hand held vacumn pump (The sort of thing you use to bleed your brakes)
to
> pull
> > a slight vacumn inside the dish. This will suck the mylar down into a
> > perfectly parabolic concave shape. You adjust the focal length by
> adjusting the
> > vacumn.
> >
> >        I used this technique at high school....um, "some" years ago..
with
> > clear film and silver spray paint (No silver mylar back then!) to make a
> > projection telescope to show a large image of a lunar eclipse for an
> astronomy club
> > open night. Our mirror was 16' in diameter, and 2' deep, and it worked
no
> > problems. We weren't perfectly airtight, so we had to keep tweaking the
> vacumn, but
> > that was probably a workmanship issue.
> >
> > Richard
> >
>
>
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