Usually when we hear the term “progressive optics” it’s in reference to bi- or trifocal glasses, that don’t have sharp lines between the different focal zones of the lenses. A group of scientists from Korea and the US, however, have recently used the technology to create something else – a prototype driver’s side car mirror that has no blind spot, yet that also doesn’t distort images in an unsafe manner.
As things currently stand – in North America, at least – only passenger-side mirrors are allowed to have a “fish eye”-type wide-angle distortion. Because that distortion causes other vehicles to appear farther away than they actually are, driver’s side mirrors are required to be flat and distortion-free. As a result, those mirrors may provide a more accurate impression of how close other vehicles are, but they also lose sight of those cars when they enter the infamous blind spot.
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One solution is to add a smaller wide-angle mirror to one corner of the driver’s side mirror, but many drivers find that such add-ons ultimately just block their view of the main mirror. Instead, Hocheol Lee and Dohyun Kim at Korea’s Hanbat National University, and Sung Yi at Portland State University, looked to progressive optics.
In eyeglasses, the different focal zones are layered one above the other. The prototype mirror, however, features three different curvatures that are arranged side-by-side. The inner zone is curved to allow for distance viewing, the outer zone is optimized for close-up viewing, and the middle zone serves as a transition between the two. As a result, the mirror has no blind spot – by the time an approaching vehicle passes off the outer edge of the mirror, it’s already visible in the driver’s peripheral vision.
Unfortunately there is some distortion of images, although the researchers believe that this is an acceptable trade-off for the benefits offered by the mirror. Importantly, the distortions do not result in other vehicles looking closer or more distant than they actually are.
Although the mirror is currently still a prototype, the researchers have stated that it would be less expensive to manufacture than conventional mirrors with added wide-angle lenses. A paper on the research was recently published in the journal Optics Letters.
Another low-distortion anti-blind-spot driver’s side mirror, that utilizes a surface made up of multiple smaller mirrors turned to different angles, is under development at Philadelphia’s Drexel University.
Source: The Optical Society