Someone figured out how to fold a 35mm effictive focal length lens into 5mm!
Here’s the abstract of the paper Ultrathin cameras using annular folded optics, by Eric J. Tremblay, Ronald A. Stack, Rick L. Morrison, and Joseph E. Ford, from the Feb 2007 issue of Applied Optics:
We present a reflective multiple-fold approach to visible imaging for high-resolution, large aperture cameras of significantly reduced thickness. This approach allows for reduced bulk and weight compared with large high-quality camera systems and improved resolution and light collection compared with miniature conventional cameras. An analysis of the properties of multiple-fold imagers is presented along with the design, fabrication, and testing of an eightfold prototype camera. This demonstration camera has a 35 mm effective focal length, 0.7 NA, and 27 mm effective aperture folded into a 5 mm total thickness.
Unfortunatey the complete paper costs US $22 for non-OSA members, but I suspect that it’s pretty unreadable by people without advanced optical systems design training anyway. Check out this summary article at PhysOrg instead, which makes sense to the rest of us.