For all-round work with a whole-plate camera, procure a rapid rectilinear of about 9J-in. focus by a ....... maker, Mich as Boss, Dallmeyer, Wray, or Taylor. The components of the lens should be of differenl foci, so that varj'ing sized plates may be used, or different angles included. A lens of this kind may be made to do duty for a variety of purposes. For example, quoting from one maker's list, a lens of 9 1/4-in. focus covering a whole plate at full aperture (f/6.3) will, when stopped down tof 11'3, cover a 10-in. by 8-in., or to f,22.6 a 12-in. by 10-in. The lens is composed of two compound lenses of 14 in. and 19 1/4 in., covering plates, when used at f 12.5, of 10 in. by 8 in. and 13 in. by 11 in. respectively. The lens is listed at £16 his. Thus, for architectural work, where a doublet is most needed, the lens might be used in its entirety, and on a 12-in. by 10-in. plate if in a confined situation. When portraits or landscapes where good perspective is an important consideration are attempted, the single components or a smaller plate must be used. It must be borne in mind that the value of the stops varies with the lens.

For example, a stop about 1 in. diameter, which, when used with the lens entire, was valued at f 8, would become, approximately, f/22 and f/32 when used with the single lenses. Lancaster's combination rectigraph is on the same principle, and costs £2 10s.