722. Daylight Exposures

Daylight Exposures. After becoming familiar with the operating of the microscope, the manipulating of the accessories and focusing of the camera, etc., you will be sufficiently experienced to proceed to the final and very important stages of exposure and development. For your daylight work, arrange the microscope and camera attachment, as in Fig. 1, Illustration No. 122, using the two-thirds objective and No. 1 eye-piece. A suitable subject should be selected. For your first experiment, the wing of a common house-fly will supply you a very good subject.

723. After killing the insect, carefully detach one of the wings and place it on a clean glass slide. Cover the wing with a thin cover-glass, and fasten the cover-glass in position with two narrow strips of gummed paper. With the specimen prepared, place the slide on the stage, securing it in position under the nickel clips. With the camera attached to the microscope, you are now ready to focus the image. With the focusing adjustment bring the objective to within one-fourth inch of the slide. The focusing must now be viewed upon the ground-glass screen.

724. Place the focusing cloth over the head and camera, excluding all light from the ground-glass. First begin by manipulating the mirror (using the piano side) to illuminate the subject. After securing even illumination, begin focusing by racking the objective upward by means of the milled head adjustment attached to your focusing rack and pinion. The focusing must be done slowly and carefully, and while turning the focusing screw observe carefully the image as it appears on the ground-glass. The subject will present the appearance of a delicate membrane studded with minute hairs and traversed with thick membrane. A fringe of very fine hairs will be found edging the wing. If they are of a foggy appearance and do not focus sharply, too much illumination is being used.

725. If the microscope is of the cheaper variety and has not the sub-stage or Abbe condenser fitted with an Iris diaphragm, then arrange the microscope and camera farther from the source of light, or insert in the tube of the microscope the second size of the interchangeable diaphragms. This latter method is preferable to the former, for the diaphragm will assist in giving you a greater depth of focus. Where the better grade of instrument is employed, which is fitted with the Abbe condenser and Iris diaphragm, reduce the illumination with the Iris diaphragm. This concentrates the light upon the object, and when dia-phragmed to the correct stage the image will stand out sharply defined without any appearance of fuzziness.

726. There being two diaphragms to the condenser, the upper one, or one next to the stage, may be used with the smallest opening, providing it covers the field. The lower diaphragm cannot be used with so small an opening, for then it would cut off the illumination on the edges of your object. This diaphragm should be adjusted so that the opening is sufficiently large to admit the entire field into the view. The exact size can only be ascertained by trial, viewing the image first through the eye-piece before attaching the camera. With the proper stop selected and the camera attached, the image may be focused on the ground-glass.

727. When the focus has been obtained, carefully slip out the ground-glass screen and insert the plate-holder in its place, exercising great care that you do not jar the instrument during this procedure.

728. The safest way to insert the plate-holder is to hold the camera firmly with the left hand while inserting the plate-holder with the right. This will avoid jarring.

The proper inserting of the plate-holder without jarring the image is of utmost importance, and one can do no better than to practice this portion of the work, without making exposures, for, strange as it may seem, the very slightest jarring of the instrument may change the focus of the light upon the image to be photographed. For this reason a very rigid and substantial table upon which to rest the instrument during exposure, is necessary.