After a few times I would have enough money to buy the mini projector, joepie!
Now I figure out with Peack lenses, meniscus lenses, mirrors, and one diapositive (35mm).
I dissanbly a dia projector and I pickend this one (condenser lens)http://www.google.be/imgres?q=condenser ... condensers
The problem is the chromatic aberration (it is not a doublet)
Nagahara's proposition is one of the best solution for a true human fov. However, the hmd has vignette problems.
The second patent is only good in dark rooms for a good vision.http://www.youtube.com/watch?v=2rvDYF7XCjw
An other posibility for less optical weight is a concave mirror in front of the observer's eye and a beamsplitter between the mirror and the eye. It can give more than 100 deg fov.
The last one would be easy with a huge polished ice spoon for example.