Ho John Lee’s Weblog

A team at Honam University in Korea has developed a low cost wide angle lens that provides the wide field of view associated with fisheye lenses, but with much lower distortion. The image above is from a wide angle camera mounted on the ceiling of a university book store. Notice the relatively straight lines of the book shelves, in contrast to the curving distortion associated with a fisheye lens.

There are already various software solutions for remapping lens distortion from captured images, but this is a much more elegant approach performing the mapping in analog space before the image is sampled. There is still a blind spot at the center of the image, where the camera blocks the conical miror.

Optics.org says the lens costs around $100, although I suspect that may be the cost of materials for the development team, and probably doesn’t include the cost of the camera. The lens assembly looks more fragile than a typical security camera, but I could also see this making a nice webcam, especially if they come up with a way to minimize/mask/move the blind spot.

Speaking to optics.org, Prof. Gyeong-il Kweon of Honam University said: “We have successfully designed a wide angle lens that can provide a FoV of over 150 degrees with less than 1% distortion, and are very excited about its potential in the security arena.”

Dubbed as a “catadioptric” wide-angle lens, it is made up of a mirror that reflects the light from a wide area (catoptric), and lenses that focus this light on the sensor of a small camera (dioptric).

The setup consists of cone-shaped mirror fixed inside a hemispherical glass dome. At the top of the dome are a series of lenses leading up to a slot for connecting a small camera. Light entering from the dome strikes the mirror and is directed toward the lens. Here, it is focused to form a sharp image at the exact location of the camera’s sensor.

Looking at some of the sample images one can’t help but notice a small black spot at the centre of every picture. This phenomenon, called central obscuration, is actually a reflection of the camera appearing on the mirror. Kweon and his research partner Milton Laikin are looking for ways to overcome this problem. Currently, they have designed a purely dioptric lens that doesn’t suffer from this problem and has a FoV of 120 °.

Link (requires free registration)

This entry was posted on Friday, December 15th, 2006 at 8:16 pm and is filed under Digital Photography and Imaging, Front Page. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.