Okta's crazy HMD project.

Post by **SinSilla** » Sun Apr 25, 2010 1:31 pm

The most higher quality Stereo-HMDs have multi-lens setups per eye (e.g trilpets), so they are using a combination of different lens characteristics to obtain a wide FoV while still
providing an almost distortion-free picture.

Without deeper knowledge of optics i don´t see a possibility to resemble such a system in a Diy-manner.

When using a (stereo) single lens system you have to come to a compromise, that would be edge-distortion, lower FoV and lower resolution.

The minimum you would like to have here should be 640x480, that limits the display choice to displays 3,5" and above (if you want to keep the price somewhat low, this includes 1000$)

One of the better ones should be the Primeview PD035VX2.
With an active area of 72,0mm x 52.56mm you know that you should look for lenses that aproach these measures.
The display should preferably be even a little larger than the lens itself for better FoV.
Suitable lenses tend do to between from 8 to 20 diopters (2x-5x Magnification) with a focal length of roughly 5cm-10cm.

When using larger Displays, e.g. the 4,8" 1024x600 unit, you will most probably need some sort of prisma in addition to your magnifying lens to shift the two images together.
(Thats where the science starts...

)

Eschenbach offers some high quality acrylic lenses that would fit 4,8" or larger displays.

If you want to experiment with lenses i would go with plano-konvex / bi-asperic /aspheric type of lenses. There is almost no way around playing with different kind of lenses to actually see what they can exactly do for you.

I decided to go the monoway (quite similar to palmers mod) since it can provide a more rewarding immersion because i prefer the wide FoV and higher Resolution over the stero3d.

Okta said that one of his most immersive experiences was with a large fresnel very close to his face in front of his monitor. I have just received different sized fresnels and did the similar, very impressive! I watched a gameplay video of an upcoming Sci-Fi Game (Black Prophecy) this way and the feeling of being there in the cockpit was so great (even though my handheld setup did miss some major keys for immersion

). 3D just can´t do this for me.

This is all a big "Afaik" since i just recently started reading and experimenting with such things.

If found the LeepVr.com Page especially useful for better understanding from the basics to the guts of an HMD. Very good!

I think it is next to impossible to diy a wide fov, high resolution stereo 3d headset without some very special tools, deep knowledge of optics and a big wallet for the two micro hd displays. But i wish everyone luck who tries nevertheless!

A very interesting HMD was the discontinued Wide5 by Fakelabs. From the looks of it they we´re using quite large displays, but i could never find any detailed technical documents.

Greetings,

Sin

Post by **PalmerTech** » Sun Apr 25, 2010 3:20 pm

Great post, SinSilla!

The real problem is not designing the optics, the knowledge is not too hard. Getting the right lenses made, though? That is the hard part... Lens fabrication is not something you can DIY easily, and making a mold for acrylic lenses costs tens of thousands of dollars.

I has also come to the conclusion that stereo3D is not possible to DIY with good specs at a decent price right now... Okta, I have been playing a bit with front surface mirrors, I think that is the key here. Basically, construct a box with two high res LCDs facing towards each other, and use matched size, light front surface mirrors to redirect the view towards the face, with circular magnification optics for each eye. Might be a bit fiddly to get working, but I know it is possible; Try researching some of the 3D photo viewers out there that use printed slides. Might even let you use our 7" screens! And actually, rear surface mirrors are probably fine for initial experimentation.

Post by **Defender** » Mon Apr 26, 2010 12:25 am

I had this idea with 3D Fotoviewers at the very beginning, however the fotos are very small which need also so small displays.

2 ideas:

1. What if we use a head mounted 7'' high resolution display and standard nvidia shutter infront for each eye. I guess the problem is to find a 120hz display of this size.
2. Mount 2x 7'' displays at 90° with a semi translucent mirror and go for a polarized setup.

Post by **Okta** » Mon Apr 26, 2010 1:20 am

Defender wrote:I had this idea with 3D Fotoviewers at the very beginning, however the fotos are very small which need also so small displays.

2 ideas:

1. What if we use a head mounted 7'' high resolution display and standard nvidia shutter infront for each eye. I guess the problem is to find a 120hz display of this size.
2. Mount 2x 7'' displays at 90° with a semi translucent mirror and go for a polarized setup.

1. Yeah not much chance of 120hz screens at the moment.

2. Nice idea! First problem for me is that none of my fresnels can be used becuase they destroy polarization but i will give this some thought, cheers!

Post by **Defender** » Wed Apr 28, 2010 11:55 pm

What is so special about the Fresnet? Can't we use simple magnify glasses.

I think a simple glass at 45° in between the two displays whould be sufficient becaus everything is dark inside the HMD?? So one would need a special semi transparent mirror.

Anyone knows how the 7'' displays are polarised?

Post by **Okta** » Thu Apr 29, 2010 8:18 am

I pulled out some realD glasses and it seems they block the light on my screen when held at a 45 degree angle so it seems possible. Hopefully ill be able to give this some more time soon.
I have very little experience with polarized so it will be interesting.
Can anyone recommend cheap large filters say 100mm square?

Post by **SinSilla** » Thu Apr 29, 2010 8:30 am

Fresnels are special because they are very thin and light, but still manage to give a decent magnification even at large sizes. It´s pretty hard to find affordable lenses which would suit a 7" display. There is one 140mmx100mm bi-aspheric plastic lens (magnifies by 2) that i´m aware of that could be used somehow theoretically. But it costs 80€ each.

But fresnels do come with a drawback, the color reproduction and sharpness of fresnels, compared to other lenses, is decent at the utmost.

And btw, just wanted to let you guys know that Vitrolight offers the Hydis 5,6" 1280x800 for 150$ since a few days, no more need to pay 340$ (which would admittedly get you a much better controller, but it´s really huge).

@Okta

Don´t they say that cellophane foil can be used for changing polarisation? I would give it a try, i guess you should have some in the kitchen. ^^

Post by **Likay** » Thu Apr 29, 2010 10:37 am

Cellophane sometimes can work like a decent retarder. Which means that one foil gives you circular polarization and yet another gives you linear polarization. Depending on how you rotated them you can adjust the resulting polarizationangle at your own wish. An almost as good shortcut is usage of a simple retarder followed by a polarizer. This works well for rotating polarization up to 90°.
If you need to retain a "sharp" polarization you always need to use an extra polarizer after the retarders. Have yet to try simple cellophane but most household plastics i've tried didn't have a special polarizationalignment. They simply only messed up the polarized light.

Post by **Okta** » Thu May 06, 2010 2:23 am

Did some playing today and it looks like plannar mirror left/right is the way to go. Next trip to the hardware i will look for some long hinges to mount the screens and mirror together and start tuning.

Post by **SinSilla** » Thu May 06, 2010 6:20 am

Sounds good! Do you still use the 7" screens for this setup?

Post by **Okta** » Thu May 06, 2010 7:11 am

Yup same screens, one in front, other on right or left. Will need counter balancing.

Post by **PalmerTech** » Thu May 06, 2010 6:30 pm

Just curious; Why a side by side, as opposed to a 90 degree top/bottom setup like most planar display set ups?

Post by **cybereality** » Thu May 06, 2010 6:31 pm

LOL! You might end up like this guy:
http://3dvision-blog.com/diy-virtual-re ... -tracking/" onclick="window.open(this.href);return false;

Post by **Okta** » Fri May 07, 2010 2:24 am

Oops i didnt mean planner rather just stereo mirror. I think it will be easier than didling around with polarizers and a silvered glass. But im still open to trying it out at this point.

Post by **PalmerTech** » Thu May 27, 2010 8:48 pm

EDIT: Woops, never mind.

Post by **Johnny-Mnemonic** » Mon Jun 21, 2010 3:19 pm

Octa, check this up, if you didn't saw it yet!
http://www.vrtifacts.com/hmds/leep-on-the-cheap/

Post by **Okta** » Wed Jun 23, 2010 9:09 pm

That looks pretty cool. Unfortunately it doesnt appear that setup could work with 3.5 inch creens which are the smallest i can find at the moment. I am also wary of teh 3m fresnel sheet to provide enough offset.
I wish i could play with all those available lenses to get the size and focul distance right for 3.5 inch screens.

Post by **crim3** » Thu Jun 24, 2010 2:21 am

Okta wrote:I wish i could play with all those available lenses to get the size and focul distance right for 3.5 inch screens.

Anyone knows of any kind of optics emulation application? Something that would plot the paths of the light rays as they go through the lenses? That would make your life a lot easier.

Post by **PalmerTech** » Fri Jul 02, 2010 1:52 am

http://www.nec-lcd.com/en/products/nl9654hl06-01j.html" onclick="window.open(this.href);return false;

Post by **Okta** » Fri Jul 02, 2010 3:56 am

Ide guess the resolution is in sub pixels and no info about a vga driver board

Playing with more lenses i am almost to the point i could use 2 3.5 inch screens tight together but the available ones have a 10mm or so bezel at the edges making it even harder >:(

My meccano will arrive soon and i will have a crack at some mirror setups,

Im intent not to let this go as i can see no help on the horizon from industry.

Big fov 3d hmd or death!!

Post by **PalmerTech** » Fri Jul 02, 2010 2:10 pm

Nope, not sub-pixels. That is a QHD display, exactly a quarter of the pixels contained in a full 1080p image. It looks perfect!

The only place I can find that will sell in low quantities wants over $900, though.

Post by **PalmerTech** » Tue Jul 13, 2010 8:27 pm

Hey man, any progress? Just wanted to check in.

Oh, and I have a favor for you, check your PMs!

Post by **Okta** » Wed Jul 14, 2010 6:42 am

Ok its not looking good. Ive tried several setups with mirrors and the best solution is single mirror left/right. The problem with using mirrors is that it increased the space and gets in the way of large lenses and makes teh resulting fov too small for what im after. Also having 1 mirrored screen means closing one eye during normal operation which is unacceptable.

Still more playing around with lenses to see if 3.5 inch screens are viable.

Post by **cadcoke5** » Wed Jul 14, 2010 8:09 am

I never pursued this, but suspect the ideal solution is a front-surface concave mirror. I have no idea how such a mirror would behave when using it at an angle. Perhaps a lady's compact magnifying mirror would be a good test.

Joe Dunfee

Post by **cadcoke5** » Sun Jul 18, 2010 8:33 am

Check out this article about military HMD's. This picture shows a curved clear mirror, apparently reflecting a display on the side of his head.

http://vresources.org/node/2468" onclick="window.open(this.href);return false;

Joe Dunfee

Post by **Okta** » Wed Jul 28, 2010 6:32 am

Update on OP.

Jon, not sure whats going on with that hmd?

Post by **PalmerTech** » Wed Jul 28, 2010 2:49 pm

It is just straight up reflecting an image from two screens using glass, maybe with a 20-30% mirror coating. Not high FOV or immersive, but useful for superimposing stuff on a real view.

Looks like great progress! Did you ever figure out the real native resolution of the screen?

Post by **Okta** » Wed Jul 28, 2010 7:11 pm

Yeah i think they're 800x480.

Post by **PalmerTech** » Wed Jul 28, 2010 7:52 pm

Gotcha. Think you might try a non-fresnel lens? Your rig looks very modular for that.

Post by **Okta** » Wed Jul 28, 2010 8:12 pm

Teh fresnels im using i scored at a 2 dollar shop. absolute bonus find as they are about 6.5 inchs and is seems you need to be pretty close to the screen size. Although they are very course and ruin the image a lot they are the best i have for now.

The biggest glass lens i have is a sqare 80mm one that is great quality but only about 3x. The killer with any lens for a single screen like this is it has to be BIG. You cant really use one lens for each eye as it adds convergance and each eyes ends up seeing its own side of the screen only so they lens needs to be big enough for both eyes to see through.

Are you using something different i can try as the imagine quality would be heaps better im sure?

Post by **PalmerTech** » Wed Jul 28, 2010 11:10 pm

Yeah, using two lenses is not very practical without other support optics.

And yes, I have something in mind.

http://www.amazon.com/Bausch-Lomb-Saver ... 195&sr=8-1" onclick="window.open(this.href);return false;

I have one of those, and let me double check to make sure it works with a 7" widescreen, but I am currently using it with an 8.9" 800x600 LCD, and it has ample viewing area.

I bet it works, the FOV might just be a little lower. You might be able to move the screen a little closer to your eyes, too! You can either just have the whole lens right in front of your nose, like it looks with your fresnel, or you can actually trim the acrylic to be closer to your eyes. Quality is leaps and bounds above a fresnel lens.

Post by **cadcoke5** » Thu Jul 29, 2010 3:40 am

I don't think the helmet I posted about above is just using a flat piece of glass for the reflector (the "Advanced Helmet Mounted Display" by L-3 Link). The specs say it has a 100 deg wide field of view, 50 deg vertical, and 30 deg view overlap. The resolution seen by each eye is 1280 x 1024. Here is the page to their specs; http://www.link.com/ahmd.html" onclick="window.open(this.href);return false;.

To get that kind of wide view, I would think the image of the display itself has to be magnified. I can't find a picture that definitively shows me that it is concave, but one view seems to suggest it is by the reflections of the outside lights. One possible source for a home-made version could be from a small panoramic mirror like those used to stick onto outside truck mirrors to allow the driver a wider view. They are silvered on the inside surface. But, I have seen tutorials about how to remove the protective paint on the back of a mirror and allow the silvered surface to be unharmed. By doing this, you end up with a front-surface magnifying mirror.

Joe Dunfee

Post by **crim3** » Thu Jul 29, 2010 4:22 am

cadcoke5 wrote:Check out this article about military HMD's. This picture shows a curved clear mirror, apparently reflecting a display on the side of his head.

http://vresources.org/node/2468" onclick="window.open(this.href);return false;

Joe Dunfee

It seems to be an excellent realization of the image I always post everytime I have a chance

(Source)
It's for a big projection system, but can be used to build a HMD with nowadays picoprojectors as seen in that military HMD.

If I ever get divorced I'll have the money and time to build my own HMD. In that case, I think I would go the picoprojectors route, specially now that I have seen that amazing HMD.

EDIT:Wrong image! Silly me, I posted in a rush. I've replaced it with the right one.

Post by **cadcoke5** » Thu Jul 29, 2010 10:57 am

Crim3, I visited your web site and read about the need for a parabolic mirror. What if you wanted to reflect to the side, but the mirror were not parabolic. The image would be distorted, but the image can be adjusted by distorting the image. This is how they do it when they are projecting video onto a planetarium off of a spherical mirror.

I just tried it by using a low-power magnifying mirror sold at Walmart. I viewed my MP3 player, which has a 2.5" screen. The concept worked and I didn't notice any distortion, except for the double image typical of a rear-silvered mirror. I really would have wanted much stronger mirror mirror. The mirror I had may not have shown the distortion because it was not strong enough. The focal length of my mirror was about 2 feet.

Just out of curiosity, I checked prices for parabolic mirrors on Edmund Optics sight... yes the prices were out of sight. Then I did an internet search and was surprised to see plenty of spherical and parabolic mirrors on Amazon.com. Most were from the education market. I saw the typical polished aluminum 12" dia parabolic mirror for concentrating sunlight. I wonder if any of these can simply be cut into two off-center parabolic mirrors? The prices start at around $26.

Joe Dunfee

Post by **crim3** » Thu Jul 29, 2010 2:23 pm

That's not my web. Things should have been a lot different for me to have such a neat and useful web.

The web explains that the mirrors have the exact shape to compensate for distortion. That's really out of the reach of a DIY system.

I've edited my post! I linked the wrong image before.

Post by **PalmerTech** » Thu Jul 29, 2010 5:30 pm

You are right, I have no idea what I was thinking. I should not post on a tired brain.

Problem is, any HMD with overlap is useless to us. There is no way to watch 3D movies or play 3D games with offset displays, which is a shame, considering that making high FOV HMDs would become VERY easy.

Hmm... I wonder if IZ3D drivers could be made to work with offset screens, shifting the view? That would be amazing!

Post by **faker** » Wed Aug 04, 2010 7:37 pm

Hi.
If you havent seen it, here is a link.
http://www.vrtifacts.com/hmds/all-brawn ... 000cs-hmd/" onclick="window.open(this.href);return false;

I also think, (I could be wrong)

That the peak 22x loupes would make excellent optics for the kopin 640x480 displays.
http://www.peakoptics.com/index.php?mai ... ducts_id=8" onclick="window.open(this.href);return false;

They seem perfect, by my random stupid calculations, a set of those would give a 50 or more fieild of view.
Am I wrong? I would like to know why if I am.

good luck guys.

Post by **PalmerTech** » Wed Aug 04, 2010 10:38 pm

Question for you, since mine are not working currently: How close can these Gigaware projectors focus exactly, and what is the image size at that point?

Post by **Okta** » Thu Aug 05, 2010 4:39 am

PalmerTech wrote:Question for you, since mine are not working currently: How close can these Gigaware projectors focus exactly, and what is the image size at that point?

I got them to focus within about 3 ro 4 inches with an image size of only a few inches across with focus by turing the focus ring past the allowed margin so it popped out inside. I had to open it up to fit it back properly.

Post by **Okta** » Thu Aug 05, 2010 4:42 am

faker wrote:Hi.
If you havent seen it, here is a link.
http://www.vrtifacts.com/hmds/all-brawn ... 000cs-hmd/" onclick="window.open(this.href);return false;

I also think, (I could be wrong)

That the peak 22x loupes would make excellent optics for the kopin 640x480 displays.
http://www.peakoptics.com/index.php?mai ... ducts_id=8" onclick="window.open(this.href);return false;

They seem perfect, by my random stupid calculations, a set of those would give a 50 or more fieild of view.
Am I wrong? I would like to know why if I am.

good luck guys.

Those lcd's in the helmet must have driver boards that reverse the image or is done in software so not an option here. That loup from a guess wouldnt come close to the standard optics. I tried a 15x loup and not much chop.