1. Outfit.
Each traveller will require to provide for his special interests; but for any archaeological work the following things are desirable. Note–books of squared paper. Drawing–blocks of blue–squared paper. Paper for wet squeezes, and for dry squeezes. Brush for wet squeezes (spoke brush). One or two so–metre tapes. A few bamboo gardening canes for markers in planning. Divide one in inches or centimetres for measuring buildings. A steel rod, 3 ft. x 1 inch for probing. Field– glass, or low–power telescope. Prismatic compass with card partly black, to see at night. Large and small celluloid protractors for plotting angles on plans. Plotting–scale, tenths of inches and millimetres. Maps of the district, the best available. Aneroid barometer, if collecting flints; small size; can be tested by observing in a tall lift, or by putting in a tumbler and pressing the hand air–tight over the mouth. The zero error, or absolute values, are not wanted for levelling, only delicacy in small variations. Magnifiers, a few pocket size; will also serve for presents. Indelible pencils, pens, and ink in strong corked pocket bottle. Reservoir pens dry up too much in some climates. China ink for permanent marking. Strips of adhesive paper, about a inch and a inches wide, to put round objects for labelling. Strong steel pliers, wire–cutting. A few pocket–knives will serve for presents. It is best to carry money in a little bag or screw of paper, loose in the jacket pocket, it in a risky district. It can then be dropped on any alarm and picked up afterwards.
Photographic.[1] In the selection of a camera much will depend upon the nature of the work to be undertaken, the conditions of travel, and the climate to which the camera will be exposed. For accurate work a stand camera is always to be preferred to one of the hand variety, and care should be taken to choose an instrument that is strongly made and of simple construction. The essentials of a good stand camera are that it shall be rigid, possess a rising and falling front, a swing back, and bellows which will be capable of extension to fully double the focal length of the lens to be used with it.
[1]Prof. Petrie is not responsible for this section, which is due to the kind assistance of some professional photographers.–ED.
The rising and falling front gives a power of modifying the field of view in a vertical direction. The swing back preserves the verticality of architectural subjects. In some cases, when used with the pivots vertical, it is a help in focussing the subject. The possible extension of the distance between the lens stop and the ground glass to twice the focal length (which is as a rule the distance between the same points, when a distant object is in focus) enables a small subject to be reproduced in natural size.
For work abroad where extremes of temperature or excessive variations have to be contended with, a special tropical camera is supplied by most of the leading makers. Its well–seasoned hard wood and metal– bound joints render it suitable for hard wear, and reduce the risk of leakage through warping or shrinkage. The tripod stand should be of the so–called threefold variety, with sliding legs which can be adapted to broken ground. If a loose screw is used for attaching the camera to the stand, a spare screw should be kept in reserve. It is important that this stand should be strongly made, and light patterns subject to undue vibrations in the wind should be discarded. For photographing small objects in the studio, a small table is more convenient than a tripod support. If the camera will not sit flat on the table, a bed can easily be designed for it. Better work will be done if this is prepared in advance than if an improvised support is used. As regards the size of the outfit, quarter–plate (3 ¼ x 4 ¼ inches) will usually be found to be large enough for the traveller. For anything in the nature of studio work in a museum or in connexion with an excavation a half–plate camera (6 ½ x 4 ¾ inches) is more satisfactory. Where a hand camera is preferred it should be one capable of adjustment of focus, and here again, strength and simplicity should be looked for. It should be provided with effective tripod legs, for studied exposures. Plates or flat films are preferable to roll fills [2] which are difficult to manipulate away from home. Flat films are less bulky and less breakable than glass, and can be sent by post. They are supplied by the makers in packs of 12 for daylight loading into a film–pack adapter, which must be provided to take the place of the ordinary dark slides for glass plates. The lens should be a modern anastigmatic by a good maker. A focal length of about six inches will be best for a quarter–plate camera. A bad lens makes success impossible even by accident.
[2] Transcriber's note: 'fills' in the original text is possibly a misprint for 'films'.
The stops will probably be of the Iris pattern, incorporated in the lens and so not likely to be lost, as often happens with loose stops.
A few words on the theory and use of the stops and on the F–notation may be of service. The speed of a photographic lens depends on the ratio of the effective aperture to the focal length. Thus any two lenses used at apertures of F/8, that is at apertures having diameters one–eighth of their respective focal lengths, should be of the same speed, though both lenses and apertures may be very different. In a given lens, the speed varies directly with the area of the aperture admitting the light, that is with the square of the diameter of the aperture. The series of stops usually employed is calculated so that each aperture is half the area of the preceding. Stated in terms of the focal length they are known as F/5.6, F/8, F/11.3, F/16, F/22.6, F/32, &c. Since the squares of those numbers, 31.4, 64, 127.7, 256, 510.7, 1024 are approximately each twice the preceding number of the series, the apertures, F(ocal length), divided by the successive numbers as denominators, are each half the area of the preceding and require twice the exposure, F/16 requires twice the 'exposure of F/11.3, and four times that of F/8, and so throughout the scale.
Stops are used to regulate either 'depth of focus' or length of exposure. The 'depth of focus' means the distance before and behind the point in theoretically accurate focus, at which objects are sufficiently focussed, for the purpose the photographer has in view. This length is greatest when only the central portion of the lens is in use. It is greatest with a pinhole, and least with a full aperture. Hence a small stop is required if the picture is to include near and far objects, while a large aperture may be used if all the subject is far enough away to be in clear focus—say more than 25 feet—or if it is a flat surface. The small stop is also required when the rising front or the swing back is in use. The power of regulating the time of exposure is convenient for shortening long exposures in dark interiors, or for lengthening inconveniently short exposures in a bright light.