Collimated display build thread...

[Mike.Powell]

One of the biggest issues regarding image quality in wide field of view systems is extraneous light. Far too many photons get loose, bounce around the room and end up back on the screen where they decimate contrast. This is true of any projection system, but in wide field of view systems the larger screen area limits your ability to hang black out curtains to capture photons which have turned to the dark side.

One cost effective approach is to reduce the screen gain so it is less responsive to extraneous light, and boost projector output to get the desired image luminance. This is exactly what Gene has done.

Behr Silver Screen is a neutral gray wall paint that you can have blended while you wait at Home Depot.

There are certainly more expensive DIY paint options, but I've yet to see a truly objective comparison. Side by side comparisons using the Mark 1 eyeball simply aren't good enough. The human eye is far too adaptive to make complex comparisons which combine elements of brightness, contrast, and color balance. Proper comparisons require proper instrumentation and methodology. [/rant mode]

[DeadlyDad]

Actually, that reminds me of a question that I forgot to ask before: What is the reason you went with one screen and one mirror, instead of two mirrors? What was the negative result of using two of them?

[wledzian]

I'm not quite sure I follow.
There's one screen because that's what's required for the system.
There's one large collimating mirror, again, because that's what's required for the system.
We use one folding mirror for each projector, because we only need one in order to put the projectors where we want them. Why would we use two mirrors?

[Tom_G_2010]

I'm not quite sure I follow.
There's one screen because that's what's required for the system.
There's one large collimating mirror, again, because that's what's required for the system.
We use one folding mirror for each projector, because we only need one in order to put the projectors where we want them. Why would we use two mirrors?

I wonder if DeadlyDad is asking "Why a Screen?" Why a folding mirror then a screen then a Collimating mirror, why not replace the screen with an inverted mirror? Just my guess maybe he'll come back with an altogether different question.

[Efe Cem Elci]

The deal with the modern collimated display design as discussed in this thread is that it successfully creates a sense of depth perception for the pilots. This creates a much more immersive experience. If Tom has it right and DeadlyDad means the use of a spherical mirror to reflect the visuals coming from a projector, this is usually used when you have non-short throw projectors and not enough space at your location to use them efficiently.

[DeadlyDad]

I'm not quite sure I follow.
There's one screen because that's what's required for the system.
There's one large collimating mirror, again, because that's what's required for the system.
We use one folding mirror for each projector, because we only need one in order to put the projectors where we want them. Why would we use two mirrors?

Efficiency. When light strikes the screen, it scatters, with only a small percentage travelling along the desired angle. If a mirror was substituted for it, almost all of the light would be reflected, and travel straight to the focal point; the user's eyes. Most collimated display patents use two mirrors, not one.

[wledzian]

Yes, the light scatters when it hits the screen. If it did not do so, there would be no image to focus on.

"Wide angle collimated" displays (the older box units) use a spherical mirror and a beamsplitter mirror. The beamsplitter essentially places the display screen at R/2, while moving it out of the pilot's way. These units cannot transmit more than 25% of the light from the source image (half is lost in the reflection from the screen to the spherical mirror, then half of that is lost on the way back to the pilot's eyes).

There are cross-cockpit collimated display patents that utilize a second spherical mirror above the first, but these work by essentially flipping a copy of the display upside-down across the horizontal axis of the screen, and projecting an unwarped image through the top-side eyepoints. This allows the mirror itself to perform the warping, but the image viewed by the pilot is still on a screen.

I did see one very interesting patent which utilized a virtual-image projector with very large optics to project an image into space, which is then reflected by one mirror to produce another image into space, which is then viewed by reflection in the primary mirror. The interesting bit about this is that it has the capacity to produce very large vertical fields of view without a physical screen getting in the way. The key thing to remember here is that any viewpoint traced from the pilot's eyes through the virtual image eventually passes back through the projector optics.

I'm genuinely curious - Please post references to the patent numbers of these displays which use two mirrors in a capacity other than what I've already described.

[jeanbrochu]

[QUOTE=geneb;116761]Ok guys, I know it's been a long time without updates, so I decided to create an "official" build thread that will show our progress.

Wayne & I have both been pretty busy with the holidays, etc. and we've not made a great deal of progress that's very photogenic.

I finished the last sheet of parts a couple of weeks ago, so now the mirror framework is ready to be assembled.

The parts:





The parts marked "TOP PLATE" and "BOTTOM PLATE" are cutting jigs. In order to properly fit the "mask" that the mylar is attached to, the top & bottom of the mirror frame has to have beveled doubler plates attached. The jig was attached to my band saw and then I tilted the saw base 20 degrees and Wayne ran the parts through it.

The doubler plates are made of 2 or 3 layers of 3/4" plywood. Here are some in the glue-up stage:



When cut, it looks like this:



The pic above shows the 2 layer bottom doubler. The top is made of 3 layers.

Here's what the cut-off from one of the top doublers looks like:



The next step will be to cut out the parts that make up the table that the mirror framework will sit on, and the base platform that the table will rest on. Some of that work should happen tomorrow (2/27/11) providing things go as planned.

The really hard work has been done - it's all down to assembly now.

We've also come up with a neat way of managing the shape of the mirror that allows us to continue to use a shop vac as the vacuum source. Here's a short video that describes the Arduino controlled bleed-air valve:



The current iteration of the firmware works much better than what is shown in the video. I'm also in the process of writing a stand-alone application that will show data from the PID controller as it does it's job and will allow us to tweak the various controller parameters real-time.

Thanks for reading folks!

g.[/QUOTE Hi Like many others I find your work on the collimated display extremely interesting. I would also like to build one
just like yours same size same design same colour. Since you went through all the design and developing process will it be
possible to purchase the DWG or DXF files for the components. I am using a CNC router 49"x49".
Many thanks in advance.
Again FABULOUS
Jean Brochu

[geneb]

No plans until at least 2017.

g.

[Tesla3D]

Saw photo on other site where you are building for friend in Colorado.
I just posted as new member today.
Any chance your friend could contact me? - Thanks