V-Rtifacts

Tag Archive: LEEP

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

 

Flight Helmet – Redux

IMHO, the Virtual Research Flight Helmet was, and still is, the ultimate head mounted display, except of course, it needed modern high resolution LCD panels. Otherwise, it had incredible field of view, great ergonomics, and unbeatable LEEP optics. I came across a more complete brochure including the retail price list (starts at $6,000.)

Flight Helmet side view

photo: Raz Fairlight

Flight Helmet Optics

photo: Raz Fairlight

One unusual aspect of the Flight Helmet was that the left and right images don’t completely overlap, producing a wider image than the normal 4:3 aspect of NTSC video. If you wanted 100% overlap, you needed to purchase prisms (3M Press-On Fresnels) to shift the images horizontally into alignment. To run the helmet monoscopically, the prisms are a must!

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.

Nothing New Under the Sun!

It’s 1985 and there’s already a nice high resolution, wide field of view VR helmet (from VPL Research), glove system, and 6 DOF tracking of both helmet and glove, thanks to Scott Fisher and NASA Ames.  In particular, check out the LEEP wide FOV optics (from LEEP inventor Eric Howlett’s predecessor company Pop Optix.) These lenses became the optical basis for the Virtual Research Flight Helmet and several of the subsequent generation of VPL HMDs. 25 years later, and these lenses are still pretty much the reference standard for wide FOV. Presumably NASA funding covered the cost of the precision molds for the huge plastic lens elements.

Take Flight in the Virtual World

By 1991, the FlightHelmet was the third HMD  to feature Large Expanse Extra Perspective (LEEP) optics from Eric Howlett’s LEEP-VR. The Flight Helmet combined LEEP’s 100° field of view with an adjustable, comfortable and rugged packaging design. The use of a rear exiting cable as a counterweight made this HMD perfectly balanced.

LEEP optics were originally used in the mid 80’s by VPL Research to produce a custom (> $100,000) HMD for NASA. In 1989 VPL followed with their own product, the Eyephones which also integrated LEEP’s optics. LEEP followed a couple of years later with their own helmet, the CyberFace.

FlightHelmet

All these LEEP based helmets suffered from the same critical problem, the only color LCDs available were in small handheld consumer TVs. All three manufacturers simply stripped down these consumer TVs and integrated their guts into a head mounted display. The effect of spreading 240 horizontal pixels over a 100° field of view made each pixel seem like a floating football from the wearer’s perspective.

CyberFace

As second issue was that the LCDs were physically too wide to match anyone’s inter-pupilary spacing (the distance between your two eyes, about 55m-70mm.) Thus the graphics system supplying the images to each eye had to calculate images which did not completely overlap; or prisms were installed in both eyepieces to resolve the incorrect spacing.

VPL Eyephones

VPL Eyephones

Epson’s entry into the small LCD (1.3″) market in 1992-1993 ended the age of LEEP helmets.

David Cassidy is Happy to Wear the Flight Helmet

David Cassidy is Happy to Wear the Flight Helmet