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.
Introduction. Much has been written in favor of and against various styles of skylights. Some recommend the single slant, others prefer the old style hip or double-slant light, while another faction advocates the perpendicular style of light. Each has its advantages and disadvantages. In the hand of an experienced operator any of these styles can be used successfully, as after all is said on the subject, it is only a matter of volume of light and its control to produce desired results.
21. In building a skylight you should first consider the size of the operating-room it is expected to illuminate. This is important, because the size of the room has everything to do with the necessary dimensions of the skylight.
22. Double Slant Skylight - In Illustration No. 1, Fig. 3, we present a double slant skylight, or what is usually termed a hip-light, with a slant of about 48°. The exact angle is of no particular importance. The top-light is about 11 feet high and 10 ft. wide, the side-light being 7 ft. from the floor at the top, and extending to within 3 ft. of the floor, thus giving a side-light of about 4 x 10 ft. This size and style of light is perhaps more in use than any other, for the reason that it can be used in a smaller space, requiring, as it does, less width of room than any other style. A room 16 to 18 ft. wide is large enough for such a light. The length of the room should be from 25 to 30 ft.- the longer the better.
23. In order to be able to make full length and group pictures, you will require the entire length of the room, to get distance in which to operate the camera. Consequently, the skylight must be located nearer to the one end of the room than to the other, only far enough from the nearest wall to allow sufficient room for backgrounds, and for operating the camera when bust and two-thirds figure work is to be made from this side of the light. With an operating room 25 ft. in length, full length figures can only be made with the subject and camera at extreme opposite ends of the room. For that reason the skylight should be located near one end; about 5 ft. from the wall is the distance advised. Where a room 30 to 40 ft. in length can be employed, the skylight should be placed nearer the center, if possible-or at least from 10 to 12 ft. from one end of the room. The advantage of this is that exposures can be made with either side of the subject lighted.
Advantage Of Double Slant Skylight. The advantage of the hip-light, such as described above, is that it is possible to work nearer the light than where a single slant is employed. With a narrow room you could not work far enough away from the single slant light to secure good results; in other words, a single slant light requires a wider room. When operating under this style of light (hip-light) handle the subject so as to receive the benefit of both the side-light and top-light. For example, in locating subjects under the light, place them at the strongest point of light, which in a hip-light is usually the center of the top-light and a few feet below, at an angle of about 45 degrees.
25. With a single slant, or perpendicular light, the strongest rays of light come from the center and a few feet above, at a 45 degree angle. Thus, with the hip-light the strongest rays fall nearer the side-light, enabling work to be done in a narrow room. The above, of course, refers to unobstructed lights. Where the light is obstructed by large buildings or trees, the location of the strongest light will be changed, usually resulting in bringing the strongest light nearer the side-light. Therefore, for all around purposes, under all conditions of outside obstruction, the hip-light is to be preferred for a narrow operating room.
Illustration No.1- Diagram of Skylights See Paragraph No. 22.