V-Rtifacts

Tag Archive: Optics

Awesome VR Optics for 1″ Class Displays At Less Than Ten Dollars!

Professional wide field of view Virtual Reality optics for less than the price of a couple of double lattes! A while back I demonstrated a design for Leep On The Cheap, a proof of concept for wide field of view optics on 3″ to 4″ display panels. Trouble was… there was quite a bit of distortion and chromatic aberration. However, it sparked quite a bit of thought and development in the VR DIY community. They’re the ones doing all the heavy lifting.

32mm Erfle Eyepiece

32mm Erfle Eyepiece

So… it’s time to come back with another optical design for wide field of view VR, but this time the optical qualities are first rate and remarkably inexpensive. Of course there are a new set of trade-offs: field of view is limited to about 65 deg. (not bad, but not totally immersive), and I rely on somewhat smaller display panels, about 1″ to 1.5″ diagonal. This is roughly the same as the: Nvision Datavisor LCD, Visette Pro, and Virtual Research VR4/V6/V8.

This design, and many commercial versions, rely a the unique characteristic of telescope eyepieces: that they can be directly used as HMD optics without modification. Even better, they’re made in fairly large quantity, with a large selection of optical characteristics and quality, and somebody else has already solved the issues of distortion, chromatic aberration, internal reflections, coatings, and aspheric design. Did I mention that they’re inexpensive. The sweet spot are either Erfle or Plossl designs; Erfle offers wider field of view. Even wider fields can be achieved with variations on the Nagler design, but the weight becomes prohibitively high.

It’s easier to give the tour by video… viddy this my droogies:

Lens sources:

30mm fl Erfle from Surplus Shed – $9.50

32mm fl Erfle from Surplus Shed – $12.50

I’ll leave you hanging re: the LCD panel. The one in the video shown above was torn from a Virtual Research V6; low res, old school.

More info on eyepieces:

Wikipedia

Common Telescope Eyepiece Designs

 

Night vision goggles of Red Army!

Suddenly, I found the information that USSR army, just before World War 2 developed electronic head-mounted infra-red night-vision goggles for tank crew! It is not exactly a virtual reality subject, but nevertheless it’s early days of electronic HMD’s in Soviet Union.

In 1993-1940 years infra-red goggles “Ship” and “Dudka” were tested by crews of BT-7 light tanks. “Ship” was developed by national optics institute and Moscow institute of glass. Device included: infra-red periscope goggles, and additional accessories for driving machinery during night.

Ship

Ship - Infra Red Night Vision Goggles

Upgraded version “Dudka” had field tests during June 1940, and after in January – February 1941. Device included: infra-red periscope goggles for tank driver, and crew commander, two infra-red beamers (by 1 Kilowatt each, 140 millimeters diameter each), control unit, separate IR signal beamer, cables and accessories for goggles.

Dudka

Dudka - Another Infra Red Night Vision System From Pre-War USSR

BT-7, light tank

BT-7, light tank

Goggles weight (without helmet-mounting) 750 gram, FOV – 24 degree, seeing distance at night – 50 meters. These devices approved all specifications of Red Army, but because of bulky construction design, usability issues, especially during winter-time, goggle construction needed additional development, which wasn’t made because of World War 2.

Tank Driver Wearing Dudka

Tank Driver Wearing Dudka

Research and development continued after WWII.

 

IR_Goggles
Upgraded, early after-war version of IR goggles (IKN-8) for T-34 tank crew

Read the whole story in English or the original Russian.

 

Why Big Helmets Still Rule

Size matters! If you ask the manufacturers of Head Mounted Displays over the past 15 years, they would echo that mantra, but it’s SMALL size that they’re boasting. Indeed, those tiny little eye glasses size VR displays look cool (from the outside), but from the inside you’re looking through a distant window. It’s hardly immersive. Read on for an explanation why bigger is better when it comes to immersion.

This illustration demonstrates why you need large lenses and therefore large displays in order to achieve very wide field of view. You’re looking at a top view cross-section of the eyeball, lens, and display. The blue lines show the extreme periphery of an unmoving eyeball’s horizontal field of view. The dim red lines demonstrate what happens when the eyeball turns to the left.

Lens and Eyeball

So… getting back to the unmoving eyeball. The lens (or multi-lens optics) is fairly close to the front of the eye, certainly as close as your sunglasses would be. The lens needs to have a diameter that is large enough to intersect the blue lines in order to allow us to see the display at that field of view. You must look through the lens for all possible angles, not around it!

Human anatomy permits extremely wide field of view because the eyeball can rotate around its center. The dim red lines show the maximum field of view with the eyeball turned to the left. Another problem is encountered: the lens must be bigger because the eye rotates around it’s center, not around its own biological lens.

Perhaps the lens could be made smaller and moved closer to the eye? More problems occur. The turning eye issue becomes magnified. Also, the lens must be aligned much more precisely with the eyeball.

We could potentially solve the turning eye problem by fabricating the lens as a contact lens, but this would require a very high diopter lens to work properly with a small display; unfortunately beyond what is possible with current contact lens technology. Furthermore, since the display is not physically coupled to the contact lens nor the eyeball rotation, the display must still be large enough to encompass all the possible rotations of the eyeball. Finally, the contact lens approach makes it difficult to transition between the virtual world and the real world, as the contact lenses must be removed and applied each time.

Now here’s the gotcha. For a display panel of any given resolution, when it is displayed at a wider field of view, it will look grainier than if displayed with a narrow field of view. You can test this one in the comfort of your own living room. Watch your beautiful 50 inch 1080p TV set from 10 feet away. Looks pretty good, huh? OK, the picture doesn’t exactly fill your visual world, in fact, most of your vision encompasses those left over pizza boxes and the other trash that you forgot to clean up last night.

Now park your nose about one foot away from the same TV set. Wow! That’s immersive! You’re getting something like 110 deg. FOV. Uh oh! What are all those dots on the screen? Sure looks fuzzy. Same 1080p resolution that looked great a moment ago at 10 feet now looks low res and grainy.

Why do you think Head Mounted Display manufacturers love narrow field of view?

LEEP On The Cheap

Build your own LEEP style wide field of view head mounted display optics. Check out the instruction video and parts list below.

In the late 80’s and early 90’s wide field of view head mounted displays were all the rage; immersion was everything! The dominant HMD vendors, VPL Research and Virtual Research shared the same optical implementation: lenses from LEEP Systems. These wide angle optics (designed by Eric Howlett of LEEP), coupled with 2″ or 3″ LCD screens really did deliver a totally immersive visual experience…except that the resolution of the LCDs were so low that under this extreme magnification each pixel looked like a football; you were swimming is a sea of colored footballs!

LCD Screens and LEEP Optics

By the mid 90’s (and up to the present) a primary design criteria for head mounted displays was small size and light weight. Indeed there are entire head mounts that weigh only a few ounces and look almost like sunglasses. Sadly, immersion and wide field of view were abandoned. The new generation of head mounts had 20 – 30 deg. field of view. You felt like you were looking through a distant window.

For reasons which I will cover in a forthcoming post, wide field of view and small/light head mounted displays are mutually exclusive. Anatomy and physics bars the way.

Almost 20 years ago I demoed an early Virtual Research Flight Helmet complete with LEEP optics. Being very impressed but unwilling to drop six grand into my first head mount, I set about building my own. The Radio Shack LCD TVs that I found were very similar to the Sony TVs in the Flight Helmet and I set about installing everything in a Friday The 13th style hockey mask. The optics were my biggest challenge, but the answer was buried in Eric Howlett’s LEEP patent, not as a claim, but as a demonstration of how to achieve wide FOV with conventional optics.

So… here’s a brief video recreating that optical design from 1991. I’ve cheated a bit by using my Android phone as the LCD screen, but otherwise the optical path is essentially the same. Aside from the phone, there’s about $25 in parts for a single eyepiece and it can display almost 90 deg. (diag.) field of view. The lens mounting is extra cheesy, but it demonstrates the optics quite well, and only takes 5 min. to assemble. So without further ado…

In the video I mention that someone needs to write an Android application to make it into a fully tracked head mount. After editing the video I remembered and tried out a couple of popular Android apps: Google Sky and Layar, both of which use the position sensors for a full 3D view. They work great with this lens system!

Parts List:

  • Anchor Optics Plano Convex Lens AX73263 43mm dia. x 77.0mm FL – $10.50 (Eyepiece)
  • Anchor Optics Double Convex Lens AX73424 62.8mm dia. x 72.4mm FL – $13.50 (Objective)
  • 2″ PVC Coupler
  • Small Sheet of Polystyrene plastic – 0.030 Black Sheet

If you were building this for real, you’d spray paint all the plastic parts to a black matte finish. LEEP also beveled the edges of the eyepiece lenses to make a better fit with the nose. To reduce weight, switch from glass lenses to CR39 plastic lenses.

If you assemble 2 of these with LCDs, you may find that the eyepieces are too far apart to match your eye spacing. Simply turn the two optical assemblies so that the LCDs point slightly outward and the eyepieces come closer together. Then apply 3M Press-On Fresnel Prisms.