Bromide Printing and Enlarging / A Practical Guide to the Making of Bromide Prints by Contact and Bromide Enlarging by Daylight and Artificial Light, With the Toning of Bromide Prints and Enlargements - John A. Tennant

A table for enlargements of from one to twenty-five times, with lenses varying in focal length from three to nine inches is here given.

ENLARGEMENTS

From the British Journal of Photography Almanac.

Focus of Lens	Times of Enlargement and Reduction
Inches	1 inch	2 inches	3 inches	4 inches	5 inches	6 inches	7 inches	8 inches
3	6	9	12	15	18	21	24	27
3	6	4½	4	3¾	3⅗	3½	3³∕₇	3⅜
3½	7	10½	14	17½	21	24½	28	31½
3½	7	5¼	4⅔	4¾	4⅕	4⅟₁₂	4	3⁹∕₁₀
4	8	12	16	20	24	28	32	36
4	8	6	5⅓	5	4⅘	4⅔	4⁴∕₇	4½
4½	9	13½	18	22½	27	31½	36	40½
4½	9	6¾	6	5⅗	5⅖	5¼	5⅟₇	5⅟₁₆
5	10	15	20	25	30	35	40	45
5	10	7½	6⅔	6¼	6	5⅚	5⁵∕₇	5⅝
5½	11	16½	22	27½	33	38½	44	49½
5½	11	8¼	7⅓	6⅘	6½	6⁵∕₁₂	6²∕₇	6³∕₁₀
6	12	18	24	30	36	42	48	54
6	12	9	8	7½	7⅕	7	6⁶∕₇	6¾
7	14	21	28	35	42	49	56	63
7	14	10½	9⅓	8¾	8⅖	8⅟₆	8	7⅞
8	16	24	32	40	48	56	64	72
8	16	12	10⅔	10	9⅗	9⅓	9⅟₇	9
9	18	27	36	45	54	63	72	81
9	18	13½	12	11⅔	10⅘	10½	10²∕₇	10⅛

The object of this table is to enable any manipulator who is about to enlarge (or reduce) a copy any given number of times to do so without troublesome calculation. It is assumed that the photographer knows exactly what the focus of his lens is, and that he is able to measure accurately from its optical center. The use of the table will be seen from the following illustration: A photographer has a carte to enlarge to four times its size, and the lens he intends employing is one of 6 inches equivalent focus. He must therefore look for 4 on the upper horizontal line and for 6 in the first vertical column, and carry his eye to where these two join, which will be at 30-7½. The greater of these is the distance the sensitive plate must be from the center of the lens; and the lesser, the distance of the picture to be copied.

In practice it is convenient, after having once found the focus for a given enlargement from a given negative with the lens in use, to mark on the base of the apparatus the point to which the lens has been extended. Then in making future enlargements of the same size, it is only necessary to set the lens at that point and move the easel backward or forward until an approximate focus is obtained, when the image will be of the proper size on the screen.

As an approximate guide it is sufficient to know that the nearer the lens is to the negative the greater will be the enlargement, as may be seen in Fig. 7. If a piece of thin cardboard, or a sheet of paper cut to the exact size of the enlargement desired, is placed upon the easel-screen, little difficulty will be experienced in getting an enlarged image of the proper size and correctly focused.

It is advisable to focus the enlargement with the largest aperture of the lens. If the lens, when working at its largest aperture, covers the plate from which the enlargement is being made, it will give proper definition over the enlargement. With a lens of the better sort, of course, the definition will be equally good whether a large or small aperture is used; but with a low-priced lens it is better to stop down to No. 8 (f/11.3) or No. 16 (f/16), to avoid spherical aberration. Stopping the lens down increases the time of exposure, and enables one to have greater control over the operation of exposing the paper, permitting time to shade or locally increase the exposure at any portion of the image. This is sometimes useful, but as a general thing stopping the lens down is not advisable, as interfering with one’s judgment in calculating exposures for various negatives. Having secured the image correct in size and focus, place thumb-tacks at all four sides of the sheet of paper or card used to focus the image. These will serve as a guide to the placing of the sensitive paper. Adjust the lens stop as desired and cap the lens, leaving the room totally dark save for such safe light as we may have for working. Place the bromide paper on the screen, using the thumb-tacks as a guide to the correct position in this.

In making his first enlargements, the beginner should avail himself of the help of test-strips. These should be about one inch wide and the length of the paper. The exposure depends on a number of factors, among which are light, negative, focal length of lens, size of enlargement, stops, sensitiveness of paper, developer, temperature of developer, and length of development. The first experiment had best, therefore, be made on a purely arbitrary basis, for which we will take ten seconds.

Pinning a test-strip on the screen, we uncap the lens and with a piece of cardboard shade two-thirds of the strip during five seconds; move the cardboard, and give the next section five seconds making ten for the first; then remove the cardboard entirely and give five seconds more, making fifteen for the first, ten for the second, and five for the third. Now develop the strip. If the fifteen seconds portion finishes development in less than one minute, and the ten takes approximately a minute, we will know that our basis was correct. But if all three were over-exposed or under-exposed, as shown by one minute’s development, we can expose the next test-strip accordingly.