Re: Collimated display build thread...
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]
Re: Collimated display build thread...
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?
Re: Collimated display build thread...
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?
Re: Collimated display build thread...
Quote:
Originally Posted by
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?
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.
Re: Collimated display build thread...
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.
Re: Collimated display build thread...
Quote:
Originally Posted by
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?
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.
Re: Collimated display build thread...
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.
Re: Collimated display build thread...
No plans until at least 2017.
g.
Re: Collimated display build thread...
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