Transparencies are treated in a similar manner to lantern slides. They may be made on any ordinary plate, or special plates are made for the purpose, having ground glass or opal backings. There is also on the market a special plate for lantern slides and transparencies, known as G. B. P. R., which by special development produce either green, blue, purple or red, or the intermediate shades. Special directions accompany these plates. The transparency should be developed a little stronger than lantern slides. After fixing and washing, the transparency should be backed with a piece of ground glass, the film, of course, being protected by the glass.

Should the amateur so elect he can make blue transparency plates by giving a previously well cleaned glass a thin coating of gelatine and when this is dry sensitizing it with the solution described on page 138, for making blue print paper. The sensitizing liquid is not applied with a brush but is poured on the center of the plate, allowed to spread to the edges and the surplus then poured off from one corner. The plate is then printed under the negative and developed the same as you would blue print paper. The depth to which to print may be judged by making a plue print from the negative first and giving the transparency the same time that you did the blue print, or the negative can be wedged into the. corner of the frame and the transparency plate placed in the same corner exactly. It can then be removed and examined and replaced in the same place. If it be desirable to place it in any other position than the corner, guides made of cardboard can be fastened to the frame, so that the negative can always be replaced in the same position. It is always desirable to have a frame or border of white glass around the transparency and this can be effected by cutting the film with a sharp knife and removing the surplus from the glass while it is still damp.

Transparency frames, made of metal, with rings to hang them up by, may be purchased from photo supply houses. These frames are made for both horizontal and upright pictures, in all the regular sizes in which dry plates are made, from 4 x 5 to11 x 14.

There will come a time when the amateur who possesses a 4 X 5 camera and who is perfectly satisfied with the quality of his negatives, will feel a longing for a larger size. As stated on page 12, the larger the camera the greater the expense for plates, trays, paper, etc. and not only this, but the greater becomes the burden when you go out for an outing with a dozen plates. A 4 x 5 negative will always make an 8 x 10 bromide print and if there is plenty of detail, it will even stand enlarging to 11 x 14 on Royal Bromide.

When enlargements are spoken of they usually mean bromide prints larger than the original negative but enlargements in the way of negatives may also be made within the limits of the largest plate which your camera will take. For example, an enlarged positive or transparency can be made in the camera as lantern slides are made. Special cameras are made for enlargements but they may also be made with the regular camera, by the use of a box and focusing cloth, as described for making lantern slides. These special cameras are similar in construction to the lantern slide camera shown in Fig. 47, except that they are made to take larger plates and the bellows is therefore not only larger, but longer. To make the matter sure, let us imagine that the camera shown in Fig. 47 is live feet long and will take plates up to 11 x 14. If now we desire to copy a photograph in the same size, our lens having a focal length of 4 inches, we would then place it in one of the kits in the front of the camera and draw back the center partition, which holds the lens, twice the focal length of the lens, or 8 inches and slide the ground glass until it was the same distance from the center of the lens. If we wished to double the enlargement we would make the distance from the center of lens to negative 6 inches, and from center of lens to ground glass 12 inches. The annexed table of enlargements is from the "British Journal Almanac" and will be found valuable when making enlargements and reductions:

Table For Enlargements

Focus of Lens.

Times of Enlargement and Reduction.

Inches.

I

2

3

4

5

6

7

8

In.

In.

In.

In.

In.

In.

In.

In.

2

4

6

8

10

12

14

16

18

4

3

2 3/4

2 1/2

2f

2 1/3

2 2/7

2 1/4

2 1/2

5

7 1/2

10

12 1/2

15

17 1/2

20

22 1/2

5

3 3/4

3 1/3

3 1/8

3

2 11/12

2 6/7

2 13/16

3

6

9

12

15

18

21

24

27

6

4 1/2

4

3 3/4

3sr

3 1/2

3 3/7

3 3/8

3 1/2

7

10 1/2

14

17 1/2

21

24 1/2

28

31 1/2

7

5 1/4

4 2/3

4 3/4

4 1/5

4 1/12

4

3 15/16

4

8

12

16

20

24

28

32

36

8

6

5 1/4

5

4*

4 2/3

4 4/7

4 1/2

4 1/2

9

13 1/2

18

22 1/2

27

31 1/2

36

40 1/2

9

6 3/4

6

5 5/8

5 2/5 5 2/5

5 1/4

5 1/7

5 1/16

5

10

15

20

25

35

40

45

10

7 1/2

6 2/3

6 1/4

6

5 3/6

5 5/8

5 1/2

11

16 1/2

22

27 1/2

33

38 1/2

44

49 1/2

11

8 1/4

7 1/8

6 7/8

6 1/2

6-5-

6 2/7

6 3/16

6

12

18

24

30

36

42

48

54

12

9

8

7%

7 1/6

7

6*

6 3/4

7

14

21

28

35

42

49

56

63

14

10 1/2

9 1/3

8 3/4

8 2/5

8 1/6

8

7 7/8

8

16

24

32

40

48

56

64

72

16

12

10 2/3

10

9 3/5

9 1/3

9 1/7

9

9

18

27

36

45

54

63

72

81

18

13 1/2

12

11 1/4

10 4/5

10 1/2

10 2/7

10 1/8

The proper use of this table can be understood from the examples given on the annexed page where the amateur desired to make a negative in the same and double the size, with a lens of 4 inch focal length. Let us take the last as an example: He consults the head of the table under "Times of Enlargement," and as he wants a double size he looks at the column headed 2. He then consults the left hand column, running his eye down it until it strikes the focal length of his lens or 4. Where these two lines meet he finds the figures 12 and 6, the former being the distance from center of lens to sensitive plate and the latter from center of lens to negative. In reducing any given number of times the same operation is repeated but in this case the larger number will represent the distance from the center of lens to the negative or picture to be copied and the lesser number represents the distance in inches from the center of lens to sensitive plate.

Now we have several times made use of the expression, focal length, when speaking of lenses and it may be possible that the amateur does not know the focal length of his lens, or how to determine it. For this reason we will endeavor to explain in simple language, how to determine the focal length of any lens. With a rule measure off on a piece of white paper 12 inches exactly, making two distinct black marks just 12 inches apart. Take your camera, paper and rule out into the yard or lawn. Pin the paper upon the side of the house or on the fence, choosing a place where you can set your camera at some considerable distance from it. With the aid of the rule mark off three inches on your ground glass, drawing two lines on the rough side of the glass with your lead pencil. Using the largest stop, proceed to bring your camera nearer to or farther from the sheet of paper on the wall until the two lines on the ground glass register, or come exactly over the two lines on the paper when viewed through the ground glass. With the aid of the rule, or a tape measure, proceed to measure the exact distance from the ground glass to the wall on which the paper is pinned. Having found this distance to be 25 feet, we proceed as follows: We divide the 12 inches marked on the paper by the space marked on the ground glass, or three inches. This gives us as a quotient 4. which is the proportion existing between the subject and the image. To this quotient we add r, making it 5, and then square it, or in other words multiply it by itself and the result is 25. We now multiply the distance from ground glass to paper, or 25 feet, by the proportion, or 4, which gives us the product, 100. This we divide by the 25 secured by adding r to the proportion 4 and squaring it and the result will be the focal length of the lens, or 4 inches. To be sure we have made it clear, let us repeat: