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Progressive Optics Ends Vehicle Blind Spots

The progressive adaptive optics technology commonly used to correct nearsightedness and reduced focusing ability has now been applied to a prototype automobile side mirror that has no blind spots and that doesn’t distort images.

Motor vehicles in the US use two types of mirrors for the driver and passenger sides: flat and spherical convex. Only passenger-side mirrors can have wide-angle-viewed mirrors because they cause objects in the mirror to appear smaller in size and farther away than they actually are. Because of this distortion, driver’s-side mirrors are required to be flat and distortion-free to provide a more accurate judgment of how close other vehicles are. But these mirrors also lose sight of cars that enter into the dreaded blind spot.

One solution, some automotive manufacturers found, was to add a smaller wide-angle mirror in the upper corner of the driver’s-side mirror, but this fish-eye lens can be distracting. Instead, scientists at Hanbat National and Portland State universities looked to progressive optics.

These images illustrate the performance between the aspheric and progressive mirror (top) and the flat and progressive mirror (bottom). In (a), the standard aspheric mirror is shown with a blue line to indicate the boundary between the two zones. This illustrates the distortion between them. In (b), the progressive prescription developed by researchers at Hanbat National and Portland State universities demonstrates the improved transition between zones, eliminating the blind spot while still giving an undistorted view of objects at a distance. (c) This is the standard flat side-view mirror compared with (d) the wider field of view of the progressive mirror. Courtesy of Optics Letters.

In eyeglasses, the different focal zones are stacked on top of each other. The prototype mirror, however, features three curvatures arranged side-by-side.

“Like multifocal glasses that give the wearer a range of focusing abilities from near to far and everything in between, our progressive mirror consists of three resolution zones: one for distance vision, one for close-up viewing and a middle zone making the transition between the two,” said Hocheol Lee of Hanbat National University. “However, unlike glasses, where the range of focus is vertically stacked [from distance viewing on top to close-up viewing on bottom], our mirror surface is horizontally progressive.” The result is a mirror with no blind spot.

“The image of a vehicle approaching from behind would only be reduced in the progressive zone in the center,” Lee said, “while the image sizes in the inner and outer zones are not changed.”

The horizontal progressive mirror does have some distortion, but the researchers believe that this is a positive trade-off for the benefits offered by the mirror. It has more than double the field of view of a traditional flat mirror, and they believe that its manufacturing cost is cheaper than conventional mirrors with added wide-angle lenses.

Another nondistorting driver’s side mirror that uses a surface composed of multiple smaller mirrors turned to different angles is under development at Drexel University. (See: Nondistorting Mirror Receives Patent)

The findings were published in Optics Letters (doi: 10.1364/OL.38.000317).  

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