Viewing Lens: He devised a sequence Camera and made series photographs of men and animals that he exhibited in motion in a viewing device he called a Tachyscope. Transparencies of the photographs were mounted on the periphery of a large disk that revolved continuously behind the lens of a projector. As each picture moved into position opposite the lens, an electric flash from a Geis-sler tube threw its image on a small viewing screen.
But in fact the picture was not a duplicate, for the viewing lens was at another point in space than the taking lens: by the phenomenon of parallax the images, particularly of subjects close to the camera, were slightly different. This discrepancy was corrected by the introduction of the single-lens reflex camera. The Mirror was now put inside the Camera body. By an ingenious spring-loaded mechanism it flipped from its 45 ° position to the horizontal on pressing the shutter release. The American Graflex (introduced in 1903) and the British Soho Reflex of three years later became the standard hand cameras of pictorial photographers for the first two decades of the century.
However, although a long focal length lens is mandatory, it need not be expensive. The utmost of critical sharpness in a portrait lens is not necessary, or even desired, since considerable diffusion can be tolerated in portrait negatives. Your lens needn't be in a shutter for strictly studio portraits, either. A lens in barrel is perfectly satisfactory, since you can provide yourself with a simple Packard shutter to use behind the lens. Many portrait men actually prefer the Packard to the more costly between-the-lens shutters.
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Photography
