[simpits-tech] So I've got this huge thing in my garage now.....

[Matt Bailey]

So digital keystone correction would not allow me to maintain a
distortion-free image were I to mount the projectors above my
head....and mirrors would only be slightly better since the mirror
assemblies would have to be near my head as well (though they may still
be necessary in order to get three projector beams in almost the same
space).

Now there is an aspect of my screen that might come into play, I
wonder: I think I mentioned this just briefly earlier, but the screen
is not symmetrical about its Z axis. That is to say, if you look at the
screen from the side, you wouldn't see a symmetrical "C" shape. Rather,
there is a curve towards the top (as it sits now), which I assume is
because the Mylar screen in the big sim was not directly in front of
the BP, but below it a bit. I wonder if this shifts the plane of the
screen such that the projectors would have to be above the screen?

Of course, this is not a huge issue if I use it as a BP screen with a
Mylar mirror in front of the cockpit, since I can put the projectors
truly in line with the screen's plane.

Matt

On Wed, 7 Aug 2013 16:35:24 +0000 (UTC)
wledzian1 at comcast.net wrote:

> In a perfect world, the optical axis of the projector would always be
> parallel to the optical axis of the screenTo move the projector away
> from the centerline (for table or ceiling mounting), the lens can be
> shifted to offset the image while maintaining this parallel
> condition. High-end projectors have an adjustable shift, cheaper
> projectors have a fixed shift and digital keystone correction. 
> 
> In order to produce a distortion-free image without further warping
> required, the projectors need to have a zero-offset projection. That
> is to say, if you were projecting a corrected image onto a flat
> plane, the projector would be directly in line with the image center.
> Furthermore, the projectors need to be centered within the screen,
> even with the horizon plane. Unfortunately, this is also where your
> head needs to be. You can get away with having the projectors just
> over your head without huge amounts of distortion, but the higher you
> place them, the worse the distortion will become. This effect cannot
> be overcome by further keystone correction. 
> 
> -Wayne 
> 
> 
> ----- Original Message -----
> From: "Matt Bailey" <dabigboy at cox.net> 
> To: simpits-tech at simpits.org 
> Sent: Tuesday, August 6, 2013 9:53:33 PM 
> Subject: Re: [simpits-tech] So I've got this huge thing in my garage
> now..... 
> 
> Wayne, I cannot tell you how helpful this is. Thank you so much for 
> your insight! I think I now "get it" about the image looking right as 
> long as the viewer is at or very close to the projector (which I can 
> approximate with mirrors and keystone correction, as you pointed
> out). Looks like I may yet have to spring for some short-throw
> projectors, but that's ok. If I can put together a system for under
> $3,000 that rivals the 180* collimated displays on multi-million
> dollar commercial sims (not counting computer cost), then I think I
> will be doing very, very well! 
> 
> Now that you mention it, when I went into the projection compartment
> of a level D sim and saw the BP screen lit up, it didn't appear that
> there was any funky warping going on. The image looked something like
> mine. Now, would I be correct in assuming that, if using the
> projectors inside the screen, a proper setup would not require
> software image warping, regardless of whether the pilot was viewing
> the inside of an opaque screen, or looking at a curved mirror/Mylar
> in front of the cockpit that was just reflecting the BP's image? I
> tend to think yes. 
> 
> Matt 
> 
> On Tue, 6 Aug 2013 16:24:57 +0000 (UTC) 
> wledzian1 at comcast.net wrote: 
> 
> > Regarding the projection of a flat image onto a curved screen
> > without the need for pre-warp- Note that this only applies to the
> > case where the screen is used as a RP screen with the projectors on
> > the inside. A front-projection setup where the inside surface is
> > the viewing surface (the projectors and the viewer are inside the
> > screen) cannot work without warping, as the projectors and the
> > viewer would need to occupy the same spot. 
> <snip> 
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