This section is from the book "Complete Self-Instructing Library Of Practical Photography", by J. B. Schriever. Also available from Amazon: Complete Self-Instructing Library Of Practical Photography.
Condensing Lenses. In Illustration No. 15 is shown a section of a dark-room used for Bromide enlarging. The camera employed is an ordinary view camera, and the illumination is supplied by an electric arc-light hung on the outside of the partition. Fitted in the partition and between the arc-light and the camera is a pair of 9-inch condensing lenses, and in the space for the plate-holder is fitted a negative-holder, which operates exactly the same as a plate-holder.
Illustration No. 15-Section of Dark-room Used for Enlarging-See Paragraph No. 621.
The Negative-Holder. The negative-holder consists of a wooden frame fitted with different size kits to hold different size negatives. The holder is so constructed that the kits can be used upright or crosswise. A very practical and inexpensive negative-holder may be made by using an old discarded plate-holder, cutting out the division which separates the two plates when used as a double holder. This holder may then be fitted with the regular kits used for plate-holders, so any size plate may be employed, from 4x 5 to 8 x 10 inches, and, as the ground-glass frame of the regular view camera is reversible, the holder may be inserted in an upright or horizontal position, by simply inverting the ground-glass frame which receives the plate-holder. When using the condensers, of course you dispense with the ground-glass but use the frame, for the spring frame will be required to hold the plate-holder, containing the negative, in place.
623. The lens employed is an old style 4-4 Darlot Portrait Lens. Over the front flange is fitted a wooden block, with an opening as large as the lens. The face of the block contains a groove, into which is slid a piece of ruby glass, which is used in front of the lens when pinning up the sensitized Bromide paper.
624. After focusing the image on the screen the ruby glass is slid into the groove, excluding all white light, but supplying sufficient non-actinic light to enable you to attach the Bromide paper to the easel, without fogging the paper. When ready for the exposure, first turn off the electric light, by means of a switch to the left of the camera, and then withdraw the ruby glass from the groove before the lens. Then turn on the light and make the exposure.
Folmer And Schwing Enlarging Camera Without Condensers. Generally it has been thought necessary, when making enlargements, to have apparatus fitted with condensers, in order that the best of results may be secured. The expense connected with the fitting up of an apparatus that will take negatives up to, and including, the 8 x 10 size, or even the 5x7 size, is more than the average photographer cares to incur. The Folmer and Schwing Enlarging Camera does away entirely with condensers, using ground-glass in their place to distribute the light evenly over the whole surface of the negative.
626. Although this enlarging camera is intended to be used with an arc-light, it is possible to employ it with daylight or any other source of illumination. The most important factors, however, to be taken into consideration in selecting an illuminant are, first, the strength of the light, and second, its uniformity. The light should be strong enough to permit of short exposures when using a small stop, and also be perfectly uniform, so that an exact amount of exposure may be given a negative, at any and all times, to produce identically the same results.
627. Daylight varies in its intensity not only every hour of the day, but seldom on any two days is it exactly the same. The Aristo lamp or any arc-light will be found a very satisfactory form of illuminant, as either gives a uniformly even light.
628. Illustration No. 17 shows the Folmer and Schwing enlarging apparatus specially constructed for the purpose. The camera is attached to the inner wall of the dark-room and, fastened to the outer wall, is a cone which connects with the arc-lamp. The bellows of the camera permits of liberal extension, the bed being in telescopic form.
629. The size of the enlargement is, of course, regulated by the focal length of the lens used, and by the distance of the easel-to which the Bromide paper is attached -from the camera. The most perfect prints can be made uniformly and economically by this simple and inexpensive method. A frame is inserted between the back of the camera and the wall, into which the negative is inserted in position, and in which also one or more sheets of ground-glass are placed. The object of the ground-glass is to diffuse the light and equally distribute it over the negative.
630. The shape of the cone permits of a collection of strong light at the narrow entrance, and as it falls on the ground-glass this will distribute over the entire space, illuminating all portions of the plate to approximately the same degree. By this method it is not necessary to procure expensive condensing lenses, and one may enlarge from 8 x 10, or even larger, negatives by bringing into commission a camera of the proper size and by constructing a cone large enough to carry the rays of light to the negative.
631. It should be borne in mind, however, that the source of illumination must be farther from the negative when employing the larger plate. Under no circumstances should the distance from the light to the plate be less than twice the diameter of the plate. At this distance, however, perfectly even illumination will be secured. The nearer the light is to the negative the shorter will be the required exposure. The current should be turned off when the enlarging apparatus is not in actual use, for the carbon throws off considerable heat when burning, and also uses considerable electricity. It is, therefore, very essential to have a switch located in a convenient place, so the current may be turned on and off at will.
632. A practical arrangement will be observed in Illustration No. 15, which shows a regular section of a dark-room conveniently arranged for enlarging. (See page 227.)
Illustration No. 16 Ingento Enlarging and Copying Easel See Paragraph No. 615.
Illustration No. 19 Artificial Illumination for Enlarging and Reduction Using Two Lights See Paragraph No. 880.
Illustration No. 17 Former and Schwing Enlarging. Apparatus. See Paragraph No. 628.
I Ionic-Made Apparatus without Camera.
Illustration No. 18- See Paragraph No. 633 Home-Made Enlarging Apparatus.