MICROPHOTOGRAPHY The production of photographs of micro scopic size by means of the microscope. Micro photographs were at one time produced in large numbers for inserting into penholders, etc., but since the introduction of dry plates micro photography has become practically obsolete.
The wet collodion process is essential for this work owing to the structureless nature of the collodion film, and the extremely fine grain of the silver deposit. An objective of i in. or if in. focal length is the most suitable lens. A camera is not required, as the prepared plate can be fixed to the microscope stage and exposed in that position. The operation must, of course, be carried on at night time, or in the dark-room. A clean, bright negative of the object is first made on an ordinary dry plate. The micro scope, with the eyepiece removed and the objective in place, is put into a horizontal position, and the negative is placed at a distance of about z ft. from the lens. The open end of the microscope tube faces the negative. The most convenient arrangement for staging and illumi nating the negative is a large box with one hole, slightly smaller than the negative, cut in the side, and another in the top, to serve as a chimney. The negative is secured in front of the hole by drawing-pins with a piece of ground glass or tissue paper behind it to diffuse the light. A lamp is placed behind the diffuser to illuminate the negative. The image of the
negative given by the objective is now roughly focused on a piece of white card placed on the stage of the microscope, which is moved to and fro until the image is of the required size. The centre of a glass slip is coated with collodion and sensitised and transferred to the Microscope stage. A sheet of cardboard is placed over the negative while the sensitised slip is being placed in position. The card is removed, and the image carefully refocused on the sensitised collodion, which makes an excellent focusing screen. Asa small portion of the film will be fogged during focusing, before the exposure is made the card is replaced, and the slide moved slightly to replace the fogged part of the film by a fresh piece. Several trial exposures of varying length are made on different portions of the film, and the slide is then developed and fixed. Pyro and acetic acid should be used for development, as the deposit given by this reducer is of finer grain than that produced by an iron developer. The microphotograph, of course, requires the microscope or magnifying lens to resolve its details. The amount of reduction which the process will allow is limited by the size of the granules of the silver deposit, but the details of a half-plate negative are easily visible in a micro-photograph having as small a diameter as in.