Tangents
A New <i>Camera </i>
(L) Limited depth of focus of today's cameras; (R) Light-field image with everything in focus. Photo: Pelican Imaging
Until now, all cameras - from the earliest box cameras of Nicephore Niepce and Fox Talbot in the 1820s to mobile phone cameras to the latest digital SLRs - have one basic feature in common. They are based on pinhole design. In other words, the light rays arriving from the scene in front enter the camera through its lens and fall on the light-sensitive sensor at the back of the camera. This sensor collects and “fixes” this light, turning it into an image. The difference between digital and film-cameras is the difference in sensors. But the light-collection method remains the same. A constraint of the pinhole method is that by “focusing” the lens, or moving it back and forth, only one plane of the scene can be in sharp focus when the photograph is taken. Also, when light rays arrive at a point on the sensor, they are simply added up and we lose much information about the direction of the rays of light falling on that point. However, what if we could capture more - much more - information about the rays of light arriving from the subject? For example, what if we knew the strength and direction of each ray of light originating at each point of the scene as it arrives at the camera? This would open new possibilities. A new camera design, called light-field camera, uses a large number of lenses instead of a single lens to collect this information. Like many others, this idea originates with Leonardo da Vinci. He argued that if we knew all the light rays arriving at a point, then we could reconstruct any view that could be seen from that point. Because it is extremely difficult to make such a camera, we had to wait until now. The breakthrough is to use a row of tiny lenses, called micro-lenses, in front of the sensor. These lenses capture light coming from different directions and construct a light-field which is captured by the sensor. High-speed computers and sophisticated software then manipulate this light-field to recreate the scene in different ways. (Incidentally, one of the main challenges facing the design of this software is to correct for parallax introduced by the lenses.) For example, one of the most annoying problems facing the photographer is the out-of-focus photograph. The lens focuses on the wrong part of the scene or misses focus altogether. No matter how much time one spends with Photoshop, an out-of-focus photograph cannot be corrected. With light-field cameras, the focus point can be decided after the photograph has been taken. So you look at the picture you have just taken and decide which part you want to be sharply detailed; the software does the rest. Several companies are introducing light-field cameras. Pelican Imaging makes these cameras for mobile phones. Lytro makes a hand-held light-field camera. A third company, Raytrix, makes very expensive (over $25,000) light-field cameras for industrial use. The light-field camera might just change the landscape of photography.
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