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

[Matt Bailey]

OK, so I got out my projector and played with this thing last
night....it looks INCREDIBLE! I think I have finally established
something: I'm pretty sure the DLP projectors I'm using are brighter
than the CRT projectors used by the big guys. I tried setting my
projector at one corner and shooting it onto the opposite corner of the
screen....the resulting image on the outside of the screen looked
beautiful, and just as bright as my front projection on a traditional
flat screen. So, this leaves open the first idea of using the BP just as
it was intended, along with a Gene-Screen.

Thanks for the clarification on the screen's name. :) The sim guys
called it a "BP screen" (for back projection, I assume).

I also tried front-projecting and then sitting behind the screen (one
of the initial ideas). Unfortunately I would have to do some serious
re-arranging in the garage to set this up properly...all I could really
tell is that it does work, the brightness is still excellent, but I
think I may end up with more light scatter. I'm also concerned about
strange optical effects. I think what you say about the inside optics
directing stray light back to the projector is spot-on....there is some
weird stuff going on when rear-projecting and sitting behind the
screen, at some angles you get an unpleasant reflection from the
projector (almost as bad as looking straight at the projector lens). I
don't know how bad this would be when front projecting...again, I'll
have to move some stuff around to properly test this out.

I'm VERY curious about your comment about not needing to pre-warp the
image if I use rear projection. I will say the projected image looks
very very good with no pre-warping, but it appears I am still getting
some distortion. I don't see how pre-warping could be avoided, I am
still putting a flat image onto a curved screen. Or are you saying that
once I mirror it with a curved mirror, this will make the distorted
image look right? Pre-warping is a big problem for me now, because NO
ONE has any pre-warping software for Linux. And even if I pre-warp in
software, I will be losing a lot of X-Plane's render area. The only way
around THAT problem is to spend $750 per PC to buy a "professional"
X-Plane key and use its built-in projection warping (which I hear is
very good).

Clarification on the sizes: I did some more precise measuring last
night, and the actual diameter of the top (smaller) arc is 10ft. Screen
height is 4ft. And that brings me to another complexity....it appears
this is not a simple symmetrical sphere. One bow (the top, as it sits
right now) is smaller diameter than the bottom bow. I assume this is
because the Mylar screen sits BELOW the BP screen, and I actually have
the BP screen sitting upside down right now.

Another issue: I don't know where I'm going to get big enough Mylar
sheets for this. It seems like the widest roll you can order is under
5ft. That won't work, the BP screen itself is already 4ft tall.

If I ended up using the BP screen as my main screen, and projected
inside the screen, I could always paint the inside surface, worst case
scenario. I would lose most of the distance effect and consistent
viewpoint, but it would probably still look REALLY good. Or, again, if
I can project THROUGH the screen from the front, that would allow me to
put the screen as close to the cockpit as I want, AND still use my
cheap standard-throw projectors (just need plenty of room out in front
of the sim). This will probably be my fallback plan if I can't source
big enough Mylar sheets, plus it prevents me having to "marr" the
screen with paint.

Some pics....the image is not as blurry in real life, it looks blurry
here because of the brightness I think:

http://www.flickr.com/photos/alfamatt/9445916915/

http://www.flickr.com/photos/alfamatt/9445918187/

Matt

On Mon, 5 Aug 2013 18:27:52 +0000 (UTC)
wledzian1 at comcast.net wrote:

> Matt, 
> 
> First, what you have is not a collimator, it is a screen. Not picking
> nits, just trying to work with correct vocabulary. Moreover, given
> what you say about the 'optics' on the inside surface, I have a
> feeling that it is a screen specifically intended for rear
> projection, that is to say that the intent is to have the projectors
> on the inside and the image on the outside. The 'optics' serve to
> reduce the acceptance angle from the back side, improving image
> contrast by increasing the amount of light gathered from the
> direction of the projectors, and reducing the amount of light
> gathered from the rest of the screen. This same effect also reduces
> the light bleed from the rest of the screen to any point, by
> directing the backscatter back towards the projector. The tradeoff in
> this arrangement is that it won't likely make a very good
> front-projection screen, nor will it work all that well if
> back-projected in the wrong direction. All this is speculation based
> on high-contrast rear projection screens that I've seen, and yours
> may be different. 
> 
> Second, placing the projectors within the screen doesn't allow for a
> smaller mirror. The mirror and screen geometry are intimately joined
> by the requirement that the screen resides within the focal surface
> of the mirror. One immediate benefit of placing the projectors inside
> the screen is that you can project perspective images, and get the
> correct on-screen image with no warping required, provided the
> projection geometry is correct. I could write a whole page on this,
> but I won't bore you with the details for now. For a first-order
> approximation, the mirror will be just a little less than twice the
> width of the screen. Based on your statement of "this thing is 12ft
> wide", I'm showing a required mirror radius of 117", or 19.5 feet
> wide. Assuming your seated eyepoint is 4 feet above the floor and
> accounting for a few inches of supporting structure, the whole
> package would be about 10 feet tall. 
> 
> -Wayne 
> 
> 
> 
> 
> 
> ----- Original Message -----
> From: "Matt Bailey" <dabigboy at cox.net> 
> To: simpits-tech at simpits.org 
> Sent: Sunday, August 4, 2013 2:27:53 PM 
> Subject: Re: [simpits-tech] So I've got this huge thing in my garage
> now..... 
> 
> Thanks guys, I may just do that. I assume you need vertical and 
> horizontal FOV, height, and diameter? 
> 
> I am not sure which way I am going with this yet......there are
> several options. The original setup is almost identical to Gene's,
> with one key difference. On Gene's rig, the projectors are in front
> of the cockpit, and use direct projection onto the front of the
> collimator. On the big sims (on this one, at least), three CRT
> projectors (of highly specialized design) are mounted behind/inside
> this big ol' collimator, and shoot through it. There are two layers
> to this collimator: the inside layer is a smooth, clear piece with a
> bit of optics going on (I believe it has a moderate Fresnel effect),
> and the outer layer is frosted. This makes the projected image show
> up on the frosted layer, after passing through the inner lens. From
> there it works exactly like Gene's setup...a frame in front of the
> cockpit has reflective Mylar which is pulled with a vacuum, and
> reflects the image that's on the collimator. 
> 
> I have never really considered Gene's setup as a viable option for
> me, because of concern that I may lack the skills and tools to make a
> frame and collimator that are accurate enough to make everything look
> right. With my acquisition here, however, a significant piece of the
> puzzle is done for me. But this thing is already 12ft wide by
> itself.....the screen would be huge! I do think that having the
> projectors inside this collimator has allowed the big sim guys to get
> by with a smaller Mylar screen than otherwise possible (since no
> space is required in front of the collimator for the projector
> beams). 
> 
> I have more or less ruled out using the collimator with the 
> projectors behind it, though I am going to test that out. Aside from
> my projectors probably not being as bright as what the big sims use,
> one of the reasons I was able to acquire this thing is because the
> two layers are starting to delaminate....the glue inside is drying
> up, which causes the screen to lose a LOT of light passing through it
> (or so I'm told..it's not noticeable as it sits right now). If I do
> front projection instead (and paint the outside of the collimator), I
> can preserve almost all the light from the projector. This setup
> would essentially be exactly what Gene is doing, just on a larger
> scale. 
> 
> If I don't go with a Gene-Screen, here are a couple other options: 
> 
> 1: I could use the collimator itself as the screen, and mount it in 
> front of my sim, with the projectors above the sim, projecting
> directly onto the collimator. Again, I would need to paint the
> collimator with some reflective paint. 
> 
> 2: A second option is a variation on the above option. I could still
> use the collimator as the main screen, but I would mount the
> projectors in front of the collimator, taking advantage of the
> frosted finish to make the image project onto the screen. This is
> basically the reverse of how it was used originally. Again, the
> delamination and light loss that this collimator supposedly suffers
> would be a factor. It would also mean the entire setup would take up
> more room...BUT, the BIG advantage here is that I would have no
> clearance considerations between the projectors and the cockpit (I
> could put the screen as close or as far as I want from my cockpit). I
> also might get some sort of beneficial Fresnel effect from the inside
> layer. 
> 
> Like I said, this thing is 12ft wide, so I could use it as the main 
> screen. I have sat down in front of it several times and looked
> around at the inside surface....I think it's big enough to fill the
> view of any standard business jet if I mount it correctly to its
> geometry (IOW, any given section of the screen would be 6ft from the
> pilot's viewpoint). Using it as the screen itself is very appealing
> from a simplicity standpoint, and from the standpoint of making the
> sim mobile. Right now my sim consists of the cockpit itself (which is
> on wheels, and can easily be moved by two people), a stand with the
> projector on it, and another stand with a flat projection screen. I
> could mount this thing on a wheeled base that rolls up to the sim,
> and mount three projectors on another base to go behind/above the
> sim. Options, options! 
> 
> One thing is for sure...I am about to pull my projector down from its 
> lofty perch above my sim and have some fun with this big ol' 
> collimator. :) 
> 
> Matt 
> 
> On Fri, 2 Aug 2013 15:41:18 +0000 (UTC) 
> wledzian1 at comcast.net wrote: 
> 
> > Yep - if you ever want mirror specs to match, I can run the
> > numbers. 
> > 
> > ----- Original Message ----- 
> > From: "geneb" <geneb at deltasoft.com> 
> > To: "Simulator Cockpit Builder's List" <simpits-tech at simpits.org> 
> > Sent: Thursday, August 1, 2013 8:15:30 PM 
> > Subject: Re: [simpits-tech] So I've got this huge thing in my
> > garage now..... 
> > 
> > On Thu, 1 Aug 2013, Matt Bailey wrote: 
> > 
> > > It is exactly what it looks like....this is the back-projection 
> > > collimation screen from a level D commercial flight simulator. :) 
> > > Now what to do with it......hey Gene, I think I have the start of
> > > a jumbo-sized version of your collimated display system. :) 
> > > 
> > Take very, very good care of that thing Matt. If you can figure out 
> > the specs on the shape, Wayne could likely give you the numbers 
> > needed to build a matching mirror cell for it. 
> > 
> > g. 
> > 
> > 
> 
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