The most simple form of camera lens, is that known as the single view lens. In reality it does not consist of a single piece of glass, but of two, sometimes three cemented together, so as to appear, when examined, to be one glass. It is a most valuable lens when used for landscape (see page 109), but owing to the defect which it has of slightly distorting any straight lines near the margin of the picture, it cannot be used - except with certain precautions - for architectural subjects. It is supplied with the cheaper sets of apparatus, and will afford very fine pictures, if kept to its own particular class of work.

A more expensive lens, and the form used more commonly than any other, is (he rectilinear (sec page 108), which, as its name tells us, gives lines free from distortion. This lens might be termed the sheet anchor of the photographer. It will do for landscape, for architecture, for portraiture, for copying, and for enlarging. It is also the best lens to employ for instantaneous pictures. It consists of two achromatic lenses of precisely similar pattern, placed in a tube with their concave surfaces facing one another. Between them is a slit for the insertion of stops or diaphragms of varying size. A great advantage in the use of this form of lens is, that one lens can be removed and the other employed as a single lens, under which circumstances it gives an image double the size of that afforded by the complete arrangement. At the same time the camera must be opened out to double its former length. In choosing a camera, therefore, this power of extension should not be lost sight of.

In the wide angle doublet, or portable symmetrical lens (see page 108), we also have a combination of two lenses. This form of lens is especially valuable for taking subjects in confined situations, for it will include in the picture it gives, a great deal more than would a lens of longer focus. It is for this reason well adapted for pourtraying interiors of buildings, where the camera must be placed in comparative close proximity to the subject to be taken. It is also valuable for copying.

The portrait lens (page 109), is the most rapid of all lenses, for it was devised at a time when the chemical part of the art was backward, and when every effort had to be made on the part of the optician to lessen the time of exposure. It takes excellent portraits with the rapid plates now in the market, it can be used for copying, enlarging, or as an objective for the lantern. It is, therefore, a useful tool in the hands of an intelligent worker. At the same time it will not do for landscape photography. He who is limited to the purchase of one lens, should get one of the rectilinear form. He can afterwards add to his stock as opportunity offers, with the certainty that every additional lens will give him increasing power over King Sol. We may call special attention to a make of lenses stamped with the word "Optimus." As that name implies, they are among the best in the market.

A lens is now constructed (page 107) the rapidity of which nearly approaches that of the Portrait Lens, whilst for definition and depth of focus it is superior. This instrument is known as the "Euryscope" and possesses a working aperture of F 6. It is well suited for both portraits and landscape photographs, and for copying and enlarging is unsurpassed.

A wide-angle form of Euroscope working at F9.50 is also to be obtained (page 107). It is a most difficult lens to make, but is scarcely to be equalled for general utility.