<html><head><style type='text/css'>p { margin: 0; }</style></head><body><div style='font-family: Arial; font-size: 12pt; color: #000000'>Matt,<br><br>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.<br><br>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.<br><br>-Wayne<br><br><br><br><br><br><hr id="zwchr"><b>From: </b>"Matt Bailey" <dabigboy@cox.net><br><b>To: </b>simpits-tech@simpits.org<br><b>Sent: </b>Sunday, August 4, 2013 2:27:53 PM<br><b>Subject: </b>Re: [simpits-tech] So I've got this huge thing in my garage now.....<br><br>Thanks guys, I may just do that. I assume you need vertical and<br>horizontal FOV, height, and diameter?<br><br>I am not sure which way I am going with this yet......there are several<br>options. The original setup is almost identical to Gene's, with one key<br>difference. On Gene's rig, the projectors are in front of the cockpit,<br>and use direct projection onto the front of the collimator. On the big<br>sims (on this one, at least), three CRT projectors (of highly<br>specialized design) are mounted behind/inside this big ol' collimator,<br>and shoot through it. There are two layers to this collimator: the<br>inside layer is a smooth, clear piece with a bit of optics going on (I<br>believe it has a moderate Fresnel effect), and the outer layer is<br>frosted. This makes the projected image show up on the frosted layer,<br>after passing through the inner lens. From there it works exactly like<br>Gene's setup...a frame in front of the cockpit has reflective Mylar<br>which is pulled with a vacuum, and reflects the image that's on the<br>collimator.<br><br>I have never really considered Gene's setup as a viable option for me,<br>because of concern that I may lack the skills and tools to make a frame<br>and collimator that are accurate enough to make everything look right.<br>With my acquisition here, however, a significant piece of the puzzle is<br>done for me. But this thing is already 12ft wide by itself.....the<br>screen would be huge! I do think that having the projectors inside this<br>collimator has allowed the big sim guys to get by with a smaller Mylar<br>screen than otherwise possible (since no space is required in front of<br>the collimator for the projector beams).<br><br>I have more or less ruled out using the collimator with the<br>projectors behind it, though I am going to test that out. Aside from my<br>projectors probably not being as bright as what the big sims use, one<br>of the reasons I was able to acquire this thing is because the two<br>layers are starting to delaminate....the glue inside is drying up,<br>which causes the screen to lose a LOT of light passing through it (or so<br>I'm told..it's not noticeable as it sits right now). If I do front<br>projection instead (and paint the outside of the collimator), I can<br>preserve almost all the light from the projector. This setup would<br>essentially be exactly what Gene is doing, just on a larger scale.<br><br>If I don't go with a Gene-Screen, here are a couple other options:<br><br>1: I could use the collimator itself as the screen, and mount it in<br>front of my sim, with the projectors above the sim, projecting directly<br>onto the collimator. Again, I would need to paint the collimator with<br>some reflective paint.<br><br>2: A second option is a variation on the above option. I could still use<br>the collimator as the main screen, but I would mount the projectors in<br>front of the collimator, taking advantage of the frosted finish to make<br>the image project onto the screen. This is basically the reverse of how<br>it was used originally. Again, the delamination and light loss that<br>this collimator supposedly suffers would be a factor. It would also<br>mean the entire setup would take up more room...BUT, the BIG advantage<br>here is that I would have no clearance considerations between the<br>projectors and the cockpit (I could put the screen as close or as far<br>as I want from my cockpit). I also might get some sort of beneficial<br>Fresnel effect from the inside layer.<br><br>Like I said, this thing is 12ft wide, so I could use it as the main<br>screen. I have sat down in front of it several times and looked around<br>at the inside surface....I think it's big enough to fill the view of any<br>standard business jet if I mount it correctly to its geometry (IOW, any<br>given section of the screen would be 6ft from the pilot's viewpoint).<br>Using it as the screen itself is very appealing from a simplicity<br>standpoint, and from the standpoint of making the sim mobile. Right now<br>my sim consists of the cockpit itself (which is on wheels, and can<br>easily be moved by two people), a stand with the projector on it, and<br>another stand with a flat projection screen. I could mount this thing<br>on a wheeled base that rolls up to the sim, and mount three projectors<br>on another base to go behind/above the sim. Options, options!<br><br>One thing is for sure...I am about to pull my projector down from its<br>lofty perch above my sim and have some fun with this big ol'<br>collimator. :)<br><br>Matt<br><br>On Fri, 2 Aug 2013 15:41:18 +0000 (UTC)<br>wledzian1@comcast.net wrote:<br><br>> Yep - if you ever want mirror specs to match, I can run the numbers. <br>> <br>> ----- Original Message -----<br>> From: "geneb" <geneb@deltasoft.com> <br>> To: "Simulator Cockpit Builder's List" <simpits-tech@simpits.org> <br>> Sent: Thursday, August 1, 2013 8:15:30 PM <br>> Subject: Re: [simpits-tech] So I've got this huge thing in my garage<br>> now..... <br>> <br>> On Thu, 1 Aug 2013, Matt Bailey wrote: <br>> <br>> > It is exactly what it looks like....this is the back-projection <br>> > collimation screen from a level D commercial flight simulator. :)<br>> > Now what to do with it......hey Gene, I think I have the start of a <br>> > jumbo-sized version of your collimated display system. :) <br>> > <br>> Take very, very good care of that thing Matt. If you can figure out<br>> the specs on the shape, Wayne could likely give you the numbers<br>> needed to build a matching mirror cell for it. <br>> <br>> g. <br>> <br>> <br><br>_______________________________________________<br>Simpits-tech mailing list<br>Simpits-tech@simpits.org<br>http://www.simpits.org/mailman/listinfo/simpits-tech<br>To unsubscribe, please see the instructions at the bottom of the above page. Thanks!<br></div></body></html>