THE PHOTOGRAPHIC HISTORICAL SOCIETY OF CANADA
Zeiss Projektion Eyepiece c1925
Review by Robert Carter
This unusual little gadget is a projection eyepiece. It is used in place of the regular eyepiece on a microscope when you want to attach a camera to snap pictures of little beasties and other tiny items. I spotted it at John Bock's table tucked in with a bunch of over-sized eyepieces for stereo microscopes. This particular eyepiece was made by Zeiss in the 1920s or 30s at Jena. It measures 2¼ inches high by about an inch in diameter.
You may wonder how a piece from a microscope would show up at camera show. But, almost all camera collectors eventually come across unusual optical gadgets often made by a familiar company. And with good reason. From the earliest days of photography there has been a close tie with microscopes. Many microscope makers manufactured cameras and photographic lenses, most notably Bausch & Lomb, Leitz, Ross, Watson and Zeiss (Ev Roseborough is in the process of writing an article on this very subject for the Photographic Canadiana).
And microscopes are used to make photographs too. This is called photo-micrography -- photographs taken at greater than life-size scale using a camera attached to a microscope. Many special devices have been invented over the years to help photographers make the best photo-micrographic images. The common biology/medical microscope uses both an objective lens and an eyepiece. this arrangement is designed for viewing by eye--curvature of field is compensated for by slow adjustment of the fine focus as one views the object placed beneath the objective. When you decide to photograph the viewed image, any such curvature of field may result in a blurring of the outer parts of the image. The risk of this happening is increased by the need to fiddle with the tube length or eyepiece position to bring the image in focus on the film.
To alleviate this problem, Zeiss and other makers of the day designed a special projection eyepiece. Unlike the Huyghens eyepieces used for visual observations, which have a single element field lens and eye lens with no means of adjustment, the projection eyepiece has a three element eye lens and a single element field lens plus a means to adjust the distance between the two lenses.
The projection eyepiece is set to zero and the microscope is then adjusted for the desired image. The distance between the two lenses in the projection eyepiece can now be changed to keep the eyepiece diaphram (and image) in sharp focus at the camera's film plane over a wide range of camera extensions. A scale on the eyepiece serves as a reference for quick set up to previously used camera extensions. The magnification power of projection eyepiece is generally lower (2x or 4x) than the Huyghens (usually 10x). The difference in over all magnification is easily made up photographically.
The eyepiece I picked up at the show is marked Projektion 4--a four power magnification when used on the continental style microscopes with the 160mm tube length. The top lens is enclosed in a milled black enamel housing which is rotated to adjust the inter-lens distance. The scale and tubes appear to be nickel-plated brass.
The side of the tube is signed Carl Zeiss Jena in the style of lettering and condenser outline used in the 1930s. Below the signature is engraved Nr. 4050* which may be a catalogue number or more likely a serial number. My 1934 catalogue MIKRO 1e doesn't cover projection eyepieces.
In addition to photo-micrography, projection eyepieces are also used to project an image onto paper for hand sketching --or on to a more distance screen or wall for viewing by a number of people at once.
Modern flat-field eyepieces carefully matched to the objectives eliminated the need for these special eyepieces.
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