INCREASING THE USEFULNESS OF THE SHORT FOCUS PROJECTION LANTERN. PART 11* ROBERT TAFT, UNIVERSITY OF KANSAS, LAWRENCE, KANSAS
Students in advanced classes frequently desire copies of data or diagrams presented by the teacher through the use of lantern slides. Some tables of data are too extensive or diagrams too complicated to allow of making a satisfactory copy in the interval in which the image is shown upon the screen. Of course, references to the literature could be given, hut considerable time can be spent in copying these data already photographed. The writer has tried out the plan of using the lecture lantern as an enlarging device for such data, enlarging generally being necessary as contact prints are so small as to be difficultly legible. The results proved so satisfactory and apparently have been of such interest to a number of teachers with whom the writer has talked that a description of the process seems to be worthwhile for those who are not familiar with ordinary photographic processes. It shou!d he pointed out, however, that the use of the lecture lantern as an enlarging device is by no means new.' Elaborate equipment for enlarging is not necessary. The writer's equipment consists of Model B Balopticon (Bausch and Lomb) fitted with 43/16inch equivalent focus lens, 500-watt bulb as illuminant, and a printing frame. The enlarging consists in placing a printing frame (8" X 10" usually, as this size fits well into students' notes) containing the sensitized paper in front of the lantern, the image of the lantern slide or its negative (see below) having been previously correctly focused on white paper in the printing frame. Best results are obtained in a darkened room, although with slow papers absolute darkness is not essential. For the insurance bromide mentioned later it is necessary to make the room quite dark. If suitable means for darkening the room are not available, the work may be done a t night. The correct position of the printing frame having been obtained, i t is marked with chalk. If working in a darkened room, a small flashlight, the lens of which has been covered with red post-office paper (or painted red) has been found quite useful in locating the mark. Proper exposure is made and the print developed in the usual way. If only two or three copies are desired, prints on the ordinary grades of photographic papers may be made, but if a larger number are wanted, the following procedure may be adopted. Eastman insurance bromide, Grade A (light weight) was used as the
* Read by title, St. Louis meeting, A. C. S., April, 1928. See, for example, Hepwortb, "Book of the Lantern," E. Wilson & Co., New York, 1890.
sensitive paper. as follows:
This was developed using Crabtree's contrast developer 1. Sodium bisulfite
Hydroquinone Potassium bromide Water to make 2. Caustic soda Water to make
25 gm. 25 gm. 25 gm. 1000 cc. 45 gm. 1000 cc.
To use take equal volumes of I and I1 and dilute with six volumes of water. This should be used a t temperatures of 21 to 24'C., the time of development being around 3 to 4 minutes. An acid stop bath and fixer are used such as are given in the manufacturer's leaflets found in any package of photographic papers. Care must be taken in the exposures used with the insurance bromide, as it is a very fast paper and reverses (i.e., areas that should be dark are light and vice versa) quite easily, as can be seen from the data tabulated a t the end of this paper. As this paper is quite thin, the dried print may be used as a negative to make contact prints either by silver or blue-print process. Blue-prints are much cheaper and easier to produce. While it will he found that the enlarged print is transparent enough to pass sufficient light for printing, greater transparency may be secured by painting its reverse side with a solution of 1 part paraffin and 4 parts kerosene, or 1 part castor oil and 4 parts alcohol. The print should be dried between blotters or by heat before use. If a more permanent enlarged negative is desired, 8" X 10" plates may be substituted for the insurance bromide paper. As even slow plates are somewhat faster than this paper, it may be found necessary to reduce the illumination by the use of filters over the lens to prevent overexposing the plate. Blue-Prints.-This process consists in placing the enlarged positive in the frame and placing the sensitized sutface of the blue-print paper in contact with the enlargement and exposing to the sun for several minutes. Development consists in washing in several changes of water and then drying between blotters. Somewhat greater sharpness in contact prints can be obtained by placing emulsion side in, i. e., next to sensitive surface of the blue-print paper. In order to do this, the image in projection should be reversed, right to left. Silver Process.-For the silver process much the same procedure can be used, the blue-print paper being replaced by ordinary photographic paper. Better grades of paper make nicer prints and are more easily handled by the beginner than the insurance bromide. Among the satisfactory papers of lowest cost that have been tried are Azo grade F4; Haloid Outline special, hard; and Defender Craftsman, contrast. These can be
1930
JOURNAL OF CHEMICAL EDUCATION
NOVEMBER, 1929
obtained from most photographic dealers, or from Burke and James, Chicago. Cost and Tie.-To make a single enlargement on insurance bromide and twelve blue-prints (8" X 10") will cost for materials (paper and photographic chemicals) in the neighborhood of one and a half to two cents a copy (figured a t retail prices). If twelve enlargements are made on the better grades of paper mentioned above, the cost will be in the neighborhood of four to five cents a copy for this size, depending upon the quantity in which the paper is bought. Students can do the work themselves as the process is simple. A pair of students can make an enlargement and twelve blue-print copies in the course of an hour, exclusive of the time of drying, without extending themselves. Use of Positive and Negative.-As is well known, lantern slides are made by photographing the object it is desired to reproduce, thus producing the negative. From the negative, a positive (the lantern slide) is made by contact exposure or by rephotographing the negative. For enlarging work either positive or negative can be used. A very much smaller exposure is required with positives as the amount of light reaching the sensitive paper is enormously greater. This, of course, assumes that the negatives are of the same dimensions (or nearly so) as the positive. The writer uses an instrument taking 3'// X 41/4vplates for making negatives. As lantern slides are 3l/4" by 4", those negatives will not fit the ordinary slide holder. The difficulty was obviated by removing the sliding frame in an ordinary slide holder and fitting the remaining frame with two tracks. These were made of small lengths of wood and slotted to take the plate. In making but one or two direct enlargements, negatives will be found more satisfactory with insurance bromide as photographic reversal is less liable to occur than if a positive is enlarged. Positives, i. e., ordinary lantern slides, may be used with other types of paper, very good results being obtained with the Haloid Outline special (cf. Table I.) Focal Length of Lens.-The small focal lengths (i. e., 4" to 6" EF) are better as the depth of field in sharp focus is greater, i. e., the position of the printing frame with respect to the lantern does not have to be so accurately adjusted as with longer focal lengths; also much shorter working distances between lantern and printing frame are necessary. The writer has used a 10" EF lens but the results were not nearly as satisfactory as with the shorter focal length. writer has felt the Direct Copying with Projection Lantern.-The need for a cheap copying device as the commercial copying instruments, photostat, etc., are quite expensive. The lecture lanterns containing opaque projectors offered a possibility along this line for copying data and diagrams of size not greater than 5" X 5", the size of the opening for the object in the available opaque projector (not the Model B Baloptican pre-
Distance. slide to lens,
inches
Appro.. sze
e1argcmeat
Slide enlarged, positive or negative
Paper used
13
8 X 10
Neg.
Am
13
8 X 10
Pos.
Am
F
8 X 10
Neg.
Am
6
8 X 10
Neg.
6
8 X 10
Neg.
Outline special Outline special Insurance bromide Insurance bromide Insurance bromide Insurance bromide Insurance bromide Insurance bromide
x 211%
Neg.
10'12
1v4
10'12
I8l4 x 2'12
Pos.
10'13
1 v 4x 2v2
Pos.
11 X 16
Neg.
6
8 X 10
Neg.
6
8 X 10
Neg.
5'12
Developer
Eastman MQ Eastman MQ Eastman MQ Eastman MQ Eastman MQ Crabtree
print* poaitivc or negative
Pos. Neg.
Pos. PoS. Pos. Pos.
Crabtree
Pos.
Crabtree
Neg.
Crabtree
Pos.
Crabtree
Pos.
Crabtree
Neg.
* Positive or negative print means positive or negative with respect to slide enlarged. Thus if no reversal occurs an enlarged positive will give a negative, and an enlarged negative, a positive print. These results are included to show behavior of the insurance bromide.
viously mentioned). The instrument used reversed the image right to left as projected on paper so a mirror was used to reverse the image by changing the line of projection through an angle of 90'. On slow photographic papers an object could be obtained but it was not sharply defined and the contrast was not great. Possibly by the use of more powerful illumination and shorter focal length lenses this could be satisfactorily accomplished. Manufacturers of projection devices would do well to give this their attention as a fairly cheap copying device would he exceedingly convenient for the teacher. E. P. Jones2has offered a suggestion for copying photographs and drawings similar to that used by the writer in making copies of his enlargements. The copy is made transparent with oil and this used as the negative against photographic paper. The oil can he washed out with a suitable solvent. If a large amount of copying is to be done, a camera fitted with a back to receive photographic paper has been described by A. Wori~chek.~ I, page 1931, illustrates some of the conditions Examples.-Table necessary in obtaining enlargements with the Model B Balopticon and are given in order that any one wishing to make use of the method can form some idea of the exposures necessary and the range of sizes possible. The results are given for satisfactory enlargements from positives and negatives of very considerable contrast. Other Types of Enlarging.-The amateur photographer who has access to a lecture lantern can obtain quite satisfactory enlargements by the method described provided his negatives are small enough to go into the projector (with the device suggested under Positives and Negatives). Films may be used by binding between two clean glass plates held together with adhesive tape. Of course, the better grades of paper should be used although ordinary papers are better than special enlarging papers as the illumination is much greater than used in ordinary enlarging work. This method of enlargement may also be used to make enlargements of tabulated or graphic data suitable for framing and hanging in the lecture room or laboratory. The writer wishes to acknowledge with thanks helpful suggestions received from Mr. W. M. Hinman, Secretary of the Chicago Section of the American Chemical Society. a Science,
67, 535 (1928).
J. I. E. C., 12, 679 (1920).
