You know, I was just lamenting that the other day. When this thing is done I'm not going to lift a finger toward a sim construction project until I've had time to enjoy it.

Although I've got 15 16 channel power driver boards to assemble in order to drive the lamps in the F-15 (two panels suck up 74 channels!) and I really should get back on that at some point.

Here's another video for you guys to make fun of: http://www.youtube.com/watch?v=-DaZXqSHOjw

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On the clip: I can see no benefit from painting cloth. If you've taken the trouble of creating a smoothly curved and sanded surface of the projection surface, placing cloth over it will only increase the chance of creases forming, wouldn't it?

The collimated part, to simplify it for myself, the effect is caused by the doubling of the distance to the light emanating point? Moving your head gives the impression the projected surface is one time as far away again as the mirror?

Jamf, you misunderstand. I'm not going to paint the _cloth_, I'm going to paint the _screen_. If that doesn't give me the result I want (I'll be using Behr Silver Screen), then I'll cover it with some Rose Tendo projector screen fabric I have, which should do the job.

The end result of collimation is your eyes think that what you're looking at is so far away, it doesn't try to focus on it. Here's a very good description of it: http://en.wikipedia.org/wiki/Collimation

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Ah, the "paint or fabric... or even both" tripped me up.

Are you going to check the geometry of your sanded surface with a grid test pattern, before you paint it?

No, but I may cut a profile jig that will allow us to measure how "off" we are. The problem is that this is one of those things where "perfection" can certainly be the bitter enemy of "good enough".

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JAMF, 'collimation' refers to the rays from any point in the image coming to the viewer essentially parallel, as if they were coming from an infinitely distant point. The end result is not that the image appears twice as far away, but rather it appears infinitely distant, as if you were looking out a window. When this is achieved, there is no more parallax effect when you move your head around - when you move your head sideways, what is in front of you stays directly in front of you, and when you move your head forward and back there is no change in the apparent image size. The benefits are several - when you're looking out the 'window', your eyes fully relax, leading to greatly reduced eye fatigue and the feeling that the image is distant. The "stereopsis" cues (depth perception due to different viewing angles from each eye" are gone, so the image truly looks far away. The only cues to differing depth are perspective cues (closer objects appear larger) and gross motion parallax (closer objects move through your field of view more quickly). The effect has to be seen to be believed - when you take away focus and stereopsis cues, your brain fills in the gaps with what's left, and the image feels 3-D even when it's not.

Regarding the perfection required of the screen geometry - screen geometry is one of the challenges that we had to overcome. Most textbooks below graduate-level make the simplifying assumption that a spherical mirror focuses at r/2. Some of the better ones go on to state that this is a simplification and is not valid significantly off-axis, but don't go into any more detail. We've had to work out the math on our own to calculate the correct screen shape for our intended eyepoint, and it is most definitely -not- at r/2. For that scren, which is just a bit shy of 5 feet in diameter at the widest point, an error of as little as 1/4" can mean the difference between success and failure. Too close, and the image looks like it's only a few feet away. Too far, and the image doesn't form properly (similar to what happens when you try to get the best magnification with a magnifying glass - move too far away, and it just doesn't work.) We've seen this in action - the first full-size screen we built was just 1/2" too big in radius, and it took us weeks to figure out why we couldn't get a properly collimated image.

Surface finish is another story. The issues are two-fold: First, we're front-projecting onto a convex surface - the image strikes the screen at a shallow angle towards the edges, causing any imperfections to cast shadows and casting the surface texture in high relief. Second, the image is greatly magnified. That 17" high screen fills a full 40% vertical FOV - even 400-threadcount spandex looks about as smooth as burlap held at arm's length when viewed in the mirror. Gene has been working hard this week to get a smooth even finish so we can apply paint this weekend. Gene's pretty good with the sprayer, so I don't anticipate any problems.

More to come by Monday!

The sprayer isn't so much the problem as is the sanding.

Cutting a neoprene mouse pad in half and gluing 220 grid sandpaper to it works really well though. Lots cheaper than those f'ing sanding sponges too!

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