Science: Chromatic Aberration

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Charles Arthur Birch-Field, who is no crackpot, last month advertised that from ordinary black & white pictures on photographic film he could get the colors of the original scenes. Greying, Ohio-born Charles Arthur Birch-Field is a successful Manhattan artist, retired head of a large advertising agency (BirchField & Co.), trained at the Cleveland School of Art,* son of a scientist and Westinghouse partner. Last week he demonstrated his fabulous-sounding infant process.

Any photographic film that is printed as a positive, no matter how old, can be put into any projector that is fitted with a Birch-Field "iriscope," can then be projected on a screen to show the scene's original tints, somewhat faint but true. Though few except Birch-Field had suspected it, the colors had been registered in the structure of the film since its first exposure. The iriscope is a simple transparent disk that fits over the projector's lens and is dyed with the colors of the spectrum in concentric circles from blue on the inside to red on the rim.

Like the practice, the theory sounds almost too simple. When light is focused on a film by a lens, the various colors do not come to a focus at exactly the same distance from the lens. Violet and blue light are more sharply bent in their path than is red, hence focus nearer to the lens. If the blues are sharply in focus in the upper layer of a photographic film, then the reds will be in focus deeper in the film. This is well known under the name of chromatic aberration. Birch-Field's novel realization is that every film thus contains a pattern of silver atoms which, in effect, registers the original colors of the object photographed.

This pattern is not visible to the eye, nor when projected. But the light from a projector lamp is diverted by the aberration patterns into a conic shape that spreads out over the lens. Charles Birch-Field's iriscope adds the colors—reds in the outer regions of the lens, blues in the inner.

Many practical and theoretical difficulties remain before the process is perfected. Charles Birch-Field does not expect to solve the problems in his studio with his ancient, secondhand projector and crude equipment. But someone, somewhere, probably will.

* Not to be confused with Painter Charles Ephraim Burchfield, who is also Ohio-born, also trained at Cleveland School of Art.