PHOTOMICROGRAPHIC APPARATUS* HENRYDALEADDISON,MASSAC~SEITS INSTITUTE OP TECHNOLODY, MAS~A~WSETTS CAMBRIDGE,
In studying objects through the microscope the author has often wished that he might be able to record what he saw and be able to refer to it at a later date. All attempts to record what was seen by drawing were disappointments. The only method left was photography and from all the available literature little, if any, help was obtained. Practically without exception the apparatus involved was very expensive. In the July, 1927, Scientific American was found an article that offered some encouragement. The fundamental ideas of that article have been incorporated, with some modifications, in the apparatus about to be described. At that time the author possessed an inexpensive microscope; "Little Gem" is its trade name. The apparatus was designed primarily for this but may be modified to fit any microscope. In fact, since constructing it, the author has acquired a more expensive instrument and has altered the apparatus to fit it. The apparatus will be described in its original form in the hope &at many others who are in the author's position may profit by it. Many an attic laboratory boasts of a "Little Gem" and it is for the benefit of those amateur scientists that this article is forthcoming. After some experimenting it was found that a 50-watt Mazda light placed three feet from the microscope and focused upon the reflecting m k o r by two lenses w v sufficient light to give good clear negatives with an exposure of ten seconds. The time of exposure varies, however, with the opacity of the subject to be photographed. It was also found that the farther away the film was the larger the image and consequently the greater the magnification. In focusing the instrument a ground glass screen placed the same distance from the ocular as the film will be found useful. It was found that when the microscope was in focus to the eye, it was slightly out of focus to the ground glass screen. When once in focus, however, i t matters not how far the screen is removed from the ocular as the image will be found to be sharply defined. The only limiting factor is the intensity of the illumination. It is preferable to operate in a dark room, but the author has obtained some splendid photomicrographs in daylight. At one end of the base is the stand for the microscope. This should be made fairly substantial. Next to this is a cabinet divided into three compartments. The section farthest from the microscope is lined with asbestos paper and provided with a reflector, a socket, and a door or opening of some sort whereby easy access to the interior is possible. A lens of six-inch focal length is placed a t one end of this section. Eighteen inches from this is a * Winner of ten-dollar award in student contest closing January 15, 1929.
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lens of twelve-inch focal length. The cabinet is so placed that the latter lens is just twelve inches from the center of the reflecting mirror of the microscope. At the farther end of the base is a two-pole single-throw switch by which the light may be turned on. The inside of the cabinet is painted a dull black to reduce reflections. The apparatus was put together with screws and is not only very rigid but is also fairly portable. A knife switch was found to be the most satisfactory arrangement for turning on the light because with other types of switches there was more or less jar. On the top of the stand were placed four angle irons in such a position that the camera always occupies the correct position. The microscope sits in a block so fixed that it will always occupy the same position with respect to the light and the camera. A cheap, yet convenient, holder for the film was found in a Hawkeye camera. The lens was removed and the shutter so arranged that it would stay open for any desired time. With . . this camera it was necessary to use a roll of film and thus to make six exposures before developing any pictures. This disadvantage may be overcome by the use of a camera thai.employs a film pack rather than a roll. The author used the following procedure in taking photomicrographs. The subject is located and focused-with the eye. The ground glass screen is interposed and the image brought sharply into focus. The light is turned off and the camera placed over the ocular. The shutter is then opened and the light turned on for the time required for the exposure. photomicrographs made with this apparatus are very clear and show sufficientdetail for most purposes. Prints may be made directly from the negatives or if larger prints are desired enlargements may be made without loss of detail. The accompanyingillustration is representative of the work of the apparatus. The author keeps all the prints in a filing cabinet and mounts them on filing cards with the following information: (1) number, (2) subject, (3) exposure in seconds, and (4) on the back of the card, any remarks. Negatives and prints are filed by number: e. g., 3.2 indicates photomicroWINGOF HOUSEFLY
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graph number three and cartridge number two. Negatives are filed similarly but in separate envelopes. The subjects are listed alphabetically in a card index so that any print or negative may be readily referred to. Students who are taking any courses where work with the microscope forms a major part of the work will find that this provides a means of keeping fresh in the mind, and for review purposes, the objects examined. This is not only a very useful instrument but it provides a pleasant sparetime hobby.
