Optimal Lenses and Lens Placement

[MaterialDefender]

This is more or less a DIY subject since the devkit is already in production. But I find it interesting enough for a new topic.

Given the somewhat unfortunate fact that noone produces displays with the optimal 2:1 aspect ratio (yet), there are two possible ways of positioning lenses. Both with strengths and weaknesses. You either get the same FOV both horizontically and vertically or optimal screen coverage. Not an easy choice.

After fiddling around with my DIY-Rift for some time now, I think I like the first option better. It reduces the effective resolution to 640x640 instead of 640x800 (which is barely noticeable at all), but on the other hand you don't have to tape the lenses or otherwise cover the area outside the actual display, giving a more natural overall impression. Despite that option 1 seems to be more future proof to me, since no adjustments will have to be made on the software side when (if) screens with the optimal aspect ratio become available.

Not sure, which of the two methods the final devkit uses, the "Carmack-prototype" from last year used option 2 if I understood that correctly, so most likely the devkit does the same.

EDIT: I totally forgot a third option, although I covered partial overlap in software in my Rift 3D-driver... Somehow it didn't occur to me that up to a certain degree this might make perfect sense in hardware too. This might even be what the devkit does. Thanks to PasticheDonkey for the hint.

[Randomoneh]

Can you say which software was used to make this image? Thanks.
I see so many more factors involved that is seems hard to discuss this in absolute terms. Nevertheless, it's worth discussing.

[MaterialDefender]

You're most likely right, but discussing it in absolute terms wasn't the intention . Doesn't look like a right or wrong thing to me at all, I'm just interested in other opinions regarding this matter.

The software: nothing fancy was used. Photoshop (and a drawing tablet). Photoshop Elements will be (very) far more than enough for sketches like this.

[PasticheDonkey]

i think cutting the lenses so they could be closer to each other while bigger would be better. this would remove areas you can't see passed your nose or the barrier between to two halves. the only problem is then any focusing adjustment becomes trickier mechanically.

on the diagram like yours they would be slightly overlapping circles with a line bisecting the intersection.

but then the problem is can you get those lens close to the eyes with the possibility of noses in the way. how much do you take off.

[MaterialDefender]

Thanks for the hint! Original post was updated accordingly. I covered partial overlap in my Rift 3D-driver, but for unknown reasons it didn't occur to me that this might make perfect sense in hardware too. Maybe I'm thinking a little bit too much about virtual things lately...

[geekmaster]

I did an experiment with fresnel lenses, where I stacked 3 elements such that the left and right edges of the images are stretched, then I trimmed the inner edge so it fit onto the upper bridge of my nose but under the inner eyebrow ridge. That places them very close to the eye, so the eyelash brushes them. The side of the fresnel lenses with ridges must be toward the eye on all 3 lenses in the stack. It gives me a view of my 7-inch Nexus 7 screen (showing a rift-compensated video), which extends beyond my normal visual borders. I can see video where my nose should be, and even at the extreme limits of rotation of my eyes. In fact, there are pixels everywhere I look with no obstructions (well beyond the limits of my eyeglasses for my normal vision).

The inner edge is cut somewhat similar to what PasticheDonkey showed above, but the other edges are more rectangular so the cover all of my field of view.

You can read more about it (with additional details) starting here:
http://www.mtbs3d.com/phpBB/viewtopic.p ... 335#p95633

If you can get the lenses close enough to your eyes (using a flat or concave inner surface), you can have a FoV beyond what is natural. Supernatural FoV.

[PasticheDonkey]

well i wouldn't have thought of it is a split second if you hadn't asked and then spent far longer mocking up an image and writing the post etc.

[PasticheDonkey]

I did an experiment with fresnel lenses, where I stacked 3 elements such that the left and right edges of the images are stretched, then I trimmed the inner edge so it fit onto the upper bridge of my nose but under the inner eyebrow ridge. That places them very close to the eye, so the eyelash brushes them. The side of the fresnel lenses with ridges must be toward the eye on all 3 lenses in the stack. It gives me a view of my 7-inch Nexus 7 screen (showing a rift-compensated video), which extends beyond my normal visual borders. I can see video where my nose should be, and even at the extreme limits of rotation of my eyes. In fact, there are pixels everywhere I look with no obstructions (well beyond the limits of my eyeglasses for my normal vision).

The inner edge is cut somewhat similar to what PasticheDonkey showed above, but the other edges are more rectangular so the cover all of my field of view.

You can read more about it (with additional details) starting here:
http://www.mtbs3d.com/phpBB/viewtopic.p ... 335#p95633

If you can get the lenses close enough to your eyes (using a flat or concave inner surface), you can have a FoV beyond what is natural. Supernatural FoV.

would maybe have to render a nose and brow etc. i think chromatic abrasion could be sorted in software as well.

[geekmaster]

...
would maybe have to render a nose and brow etc. i think chromatic abrasion could be sorted in software as well.

The perceived chromatic aberation is mainly blue (and mostly visible on text displays). In a 3D game it is rarely noticeable except when you look for it. And yes, you could adjust for it in software (as mention in the other thread).

Unlike your lens images, mine have the tops trimmed flat so the fit below my eyebrows so I can get them very close to my eyes. They must be very close to fill the entire FoV even with extreme eye rotation. In my case, I am near sighted so it is all in focus even with complete FoV coverage. Pulling the lenses away from the eye even a small amount reduces the FoV coverage quite a bit. If my focus does not work for you, you may need to add another lens element to the stack.

Stangely, after using this for larger than normal FoV, taking this off makes me very aware of natural vision occlusions such as my nose, eyebrows and cheeks (but especially my eyeglass frames and unfocused FoV outside them). Normal vision feels restriced and limited after such a "supernatural" FoV experience.

[PasticheDonkey]

...
would maybe have to render a nose and brow etc. i think chromatic abrasion could be sorted in software as well.

The perceived chromatic aberation is mainly blue (and mostly visible on text displays). In a 3D game it is rarely noticeable except when you look for it. And yes, you could adjust for it in software (as mention in the other thread).

Unlike your lens images, mine have the tops trimmed flat so the fit below my eyebrows so I can get them very close to my eyes. They must be very close to fill the entire FoV even with extreme eye rotation. In my case, I am near sighted so it is all in focus even with complete FoV coverage. Pulling the lenses away from the eye even a small amount reduces the FoV coverage quite a bit. If my focus does not work for you, you may need to add another lens element to the stack.

Stangely, after using this for larger than normal FoV, taking this off makes me very aware of natural vision occlusions such as my nose, eyebrows and cheeks (but especially my eyeglass frames and unfocused FoV outside them). Normal vision feels restriced and limited after such a "supernatural" FoV experience.

in that case moving the screen rather than lenses could adjust focus.

[geekmaster]

in that case moving the screen rather than lenses could adjust focus.

Moving the screen away brings the screen edges into your FoV. Better to increase magnification and lose a few pixels around the edges than to bring unnatural occlusions into the picture.

As it is, the edges of the FoV are not in good focus, but neither are they in real life when wearing eyeglass (like I do). That does not detract from the experience, because when you see motion in the corner of your eye you quickly rotate your head to bring the movement into the center of your FoV where you have overlapped stereoscopic convergence. In the "heat of battle", you do not notice any lack of focus around the edges...

[PasticheDonkey]

in that case moving the screen rather than lenses could adjust focus.

Moving the screen away brings the screen edges into your FoV. Better to increase magnification and lose a few pixels around the edges than to bring unnatural occlusions into the picture.

As it is, the edges of the FoV are not in good focus, but neither are they in real life when wearing eyeglass (like I do). That does not detract from the experience, because when you see motion in the corner of your eye you quickly rotate your head to bring the movement into the center of your FoV where you have overlapped stereoscopic convergence. In the "heat of battle", you do not notice any lack of focus around the edges...

well if the screen size was set so people with whatever vision required it further away could see the whole screen, then others could get focus moving it closer but would lose a bit of res.

how blurry are we talking at the centre of vision with an eye turned to full extreme? anyway this is a problem with all versions thus far.

[geekmaster]

well if the screen size was set so people with whatever vision required it further away could see the whole screen, then others could get focus moving it closer but would lose a bit of res.

how blurry are we talking at the centre of vision with an eye turned to full extreme? anyway this is a problem with all versions thus far.

My screen center is not blurry at all. I can see individual pixels. It is the screen edges that blur, but even so it is much better to have blurred VR content at the visual boundaries than just a blackened shroud.

[Randomoneh]

Did it. It's fot 7-inch 16:10 display with lenses set for IPD of 70mm.
Should be pixel-perfect simulation.

Good?

[MaterialDefender]

Looks good. Unfortunately I already ordered a pair of new lenses to hone my DIY-build. I guess now I have to search for yet another suitable lens to test this...

[KBK]

The contrast and resolution junkie in me says that single lens solutions will always be better looking than any set of stacked Fresnels.

That in stack of Fresnels, the air must be there, in order to produce the desired optical effects, and this stacking alone can ruin the CR and definition. The best case scenario is a around an overall what, 5% reduction in both CR and definition, which would look worse than the raw numbers would suggest.

A custom cut single lens is still the best bet, in my offhand analysis.

The single lens is a big advantage, when it comes to a custom cut, for the purposes of enabling eye movement. Regular optics, such as camera/projection and the like, make it so the cut has to be a specific type, but the singular interface of the HMD display and the lens make it so the DUT or lens/HMD display combo, in conjunction with the eye, can make a second cut work. and the second cut, is the one that allows for eye motion.

Glasses for human use are an example of a single cut. that cut staked with that of an aspherical as a secondary or paired concern, may be possible. But I admit I am weak on this particular subject. I suspect that the more expensive HMD's use something similar. However, eye/lens relational positioning then becomes critical. Messy subject, at best.

[geekmaster]

Yes, glass or acrylic aspherics would be better, but for a really inexpensive experiment, fresnels are good enough to give a feeling of immersion. And the pixels in the center area of of the screen were in sharp focus for me. Although the outer edges were stretched and blurred somewhat, they still added greatly to a sense of immersion, and when adjust "just right" I could read the part of the text visible at the right edge of the "Rift-warped" L4D YouTube video.

My idea was to make a simple cardboard frame with cheap dollar store lenses, similar to the one that came with my old VR Creations book, which could be attached to a tablet computer such as my Nexus 7. I published this because my experiment yielded results far better than past experiments using coarser fresnel lenses, and with lenses trimmed to fit snugly against the side of my nose and under my eyebrow ridge, the FoV exceeded what I see naturally.

Agreeing that non-fresnel lenses would be superior, I would like to duplicate this experiment with solid custom lenses that include outer offsets of 6-inch lenses, just like these fresnel magnifiers. These fresnel stacks may not be good for watching movies, but they are adequate for VR. But then my eyes are not so fussy as I get older. I used to clean my eyeglasses many times per day, but now I just adjust my head to look around the grime. I think that started when I got some scratches in my glasses and never bothered to replace them. Perhaps the blur at the edges that I do not even notice may annoy others who still clean their glasses often...

As you get older, available time becomes more precious, and expedient (quick and dirty) solutions are often more than acceptable. When younger, I was a perfectionist and needed everything scrupulously spotless. But that is not important any more. Just getting stuff done while I still can is most important to me.

I am interested to see the opinions of others who try fresnel lens stacks...

[Zoide]

Just getting stuff done while I still can is most important to me.

If you don't mind my asking: How old are you? I hope you don't have a serious disease or anything like that

[geekmaster]

Just getting stuff done while I still can is most important to me.

If you don't mind my asking: How old are you? I hope you don't have a serious disease or anything like that

This may be off topic, but you asked:

Age is not important. Other than things like high blood pressure and obesity (both of which could be controlled by diet and exercise), I have a permanent neck injury and brain injury from about 20 years ago. Typical bad knees and such, making exercise difficult. I could get disability payments, but I prefer to stay self sufficient and not get addicted to government handouts.

I still have an unusually high IQ even after my brain injury (measured with thorough professional testing). That is not necessarily a blessing, in that it scares bosses who want to feel superior, and corporations do not like when I see things I am not supposed to see, and it makes co-workers (cow-orkers) jealous when they are forced by management to follow my personal standards. I was kicked out of a "need to know" project when I easily extrapolated details that I was "not supposed to know" from what details that were provided to me. It took half my lifetime just to learn "normal" social skills (my true friends were my technical and sci-fi books back in the early decades of my life).

I own about 10,000 books, most of which I have read at least once. But the way my memory is going, I need to read them all again! Robotics and Computer Graphics and VR are my favorite subjects, and comprise a large part of my book collection.

I have always been able to accomplish everything that interested me. Few things are impossible if you believe in yourself. That is all that really matters. I could live a long time if I get away from my computer and get some exercise more often. At least I have my eight monitors mounted at standing height, and I use a high drafting chair, so I can stand and shift my weight back and forth while I work. It would be nice to have an elliptical machine in front of my desk so I could use it while working. Ellipticals constrain my knees to keep them in their normal range of motion, and cause much less pain than a treadmill for me...

Enough about my body... It is my mind that I value (or at least what is left of it). I feel like my brain injury prematurely aged my mind by 20 years or so... My parents are still alive and active even though they both had body parts removed from cancer (forms that their doctor said run in the family). So I may have that to look "forward" to as well. But not any time soon, hopefully...

Anyway, I knew as a young child that I had enough projects to last me six lifetimes, and unless I can get a reliable apprentice (I tried three times but their "significant other" slowly stole them away from me), I will never accomplish the majority of the things I really want to do... My near term projects include using my electric wheelchairs and Gen 3 night vision cameras and BST thermal imagers in FPV robots. Using the Rift in the FPV base station, of course...

I prefer to remain anonymous, due to contractual demands. However I may have disclosed too much personal information here already, so I will stop now...

[Zoide]

geekmaster: Wow! I don't know what to say... Well, it's an honor to have you here, and I hope you can accomplish your goals and live a happy life. In the meantime I think your contributions here have been very valuable, and I hope to see your superhuman FoV ideas in the consumer Rift!

[geekmaster]

geekmaster: Wow! I don't know what to say... Well, it's an honor to have you here, and I hope you can accomplish your goals and live a happy life. In the meantime I think your contributions here have been very valuable, and I hope to see your superhuman FoV ideas in the consumer Rift!

A future Rift with "supernatural FoV" would need custom lenses. The fresnel stack is just a prototype. I need to build an HMD with them so I do not need to hold my tablet PC and lenses with my hands. The real key is for the lens edges to actually touch the side of the nose, and the cheek below, and the eyebrow ridge above. That lets you see beyond your facial obstructions. And the offset portion from the edges of a 6-inch lens bends the 7-inch display to fill your full FoV.

I love building code and devices that are absolutely minimal. I want to build an "fov2go" type add-on for a 7-inch tablet using minimal cost components and effort. And for software, I want absolutely minimal code as well.

For example, here is the entire source code I published at MobileRead for my "geekmaster kindle video transcoder":
http://www.mobileread.com/forums/showth ... ?p=2074379

Here is my simple, efficient and elegant video transcoder that takes 800x600 grayscale raw video piped from ffmpeg (or any other source of raw video), then does rotate right, "no dither table" ordered dither, and 8-pixel-per-byte packing.

I can find no evidence that performing an ordered dither using a logical expression derived by applying Karnaugh mapping to a dither table has been used before.

Code: Select all

//====================================================
// raw2gmv 1.0a - raw to geekmaster video transcoder
// Copyright (C) 2012 by geekmaster, with MIT license:
// http://www.opensource.org/licenses/mit-license.php
//----------------------------------------------------
#include <stdio.h>  // stdin,stdout
typedef unsigned char u8; typedef unsigned int u32;
int main(void) {
    u8 o,to,tb,wb0[800*600]; u32 x,y,xi,yi,c=250,b=120; // c=contrast, b=brightness
    while (fread(wb0,800*600,1,stdin)) for (y=0;y<800;y++) { xi=y; tb=0;
        for (x=0;x<600;x++) { yi=599-x; o=x^y;
            to=(y>>2&1|o>>1&2|y<<1&4|o<<2&8|y<<4&16|o<<5&32)-(wb0[yi*800+xi]*63+b)/c>>8;
            tb=(tb>>1)|(to&128); if (7==(x&7)) { fwrite(&tb,1,1,stdout); tb=0; }
        }
    } return 0;
} 

My geekmaster kindle video player plays this video in realtime without flicker on eink Kindles ebook readers, and it uses fairly small code with no library dependencies, too.

On the faster Kindles (Kindle 4 and newer) you can pipeline multiple commands together to play streaming video in realtime, like this:

ffmpeg [options] | raw2gmv | gmplay

and it will play streaming video of the Internet in realtime. On the Kindle 3 and earlier, you need to either pipe in the transcoded stream, or play a saved .gmv transcoded file. One of the first videos that I transcoded to GMV format was trappy's "Living FPV 2". Awesome!

[youtube-hd]http://www.youtube.com/watch?v=K75ZnxR66Uo[/youtube-hd]

This would be GREAT on the Rift, especially with a head-tracked camera on the airplane!

[MaterialDefender]

Today I tried method 3 (overlapping field of vision in the center with a separator on the display) from my original post with a 7" screen and ~4x lenses. Can't say it worked very well. The separator was clearly visible at all times in a very annoying manner, no way the brain could ever adapt to this.

I'm not sure whether I might have overlooked something, but I can't think of anything right now. I used accordingly adjusted content and even tried to gracefully fade the stereo images to black in the center in the faint hope I could somehow fool my brain this way. But that didn't help a bit, of course.

Did anyone try this before? If so, did it work for you?

[geekmaster]

Today I tried method 3 (overlapping field of vision in the center with a separator on the display) from my original post with a 7" screen and ~4x lenses. Can't say it worked very well. The separator was clearly visible at all times in a very annoying manner, no way the brain could ever adapt to this.

I'm not sure whether I might have overlooked something, but I can't think of anything right now. I used accordingly adjusted content and even tried to gracefully fade the stereo images to black in the center in the faint hope I could somehow fool my brain this way. But that didn't help a bit, of course.

Did anyone try this before? If so, did it work for you?

@MaterialDefender: I sent you a PM regarding this post. Please read it and get back to me. Thanks.

[PasticheDonkey]

i believe you'd need greater magnification. you'd get a higher field of view as well.

[geekmaster]

i believe you'd need greater magnification. you'd get a higher field of view as well.

The 5x aspherics Palmer recommended work reasonably well on a 7-inch display if you get them close enough to your eyes. I may not be a good judge of how they work for others though -- I can free-view SBS pairs on a 7-inch display without the lenses.

[MaterialDefender]

@PasticheDonkey: I have various sets of lenses here. I used the 4x to explicitely test your overlapping field of vision suggestion.

[PasticheDonkey]

my rough estimate is that you'd need a 160 degree FoV per eye so that what is obscured would be hidden by your nose normally.

[MaterialDefender]

I agree. The FOV per eye would have to be relatively close to what you're used to in regard to the normal nose occlusion. For smaller FOVs (which make the separator on the screen a very big black artificial nose, so to speak) this clearly doesn't work very well.

Maybe a few days of wearing the device continuously would make the brain adapt to the new situation, but that's out of the question for practical use, I would say.