FOCUSSING.
In all descriptions of outdoor work focussing is apt to prove troublesome if there is any wind, owing to the cloth being blown about. This may be minim ised to some extent by sewing cords to is peculiarly suitable, allowing a wide choice as to focal length and angle of view. It is probable, however, that the average worker will prefer a lens which will permit him to obtain the maximum of sharpness when desired, and for tech nical or commercial landscape photo graphy this is practically indispensable. In this case, the purchase of a good rapid rectilinear or an anastigmat is advised. The greater rapidity of the rectilinear and anastigmat types of lenses must not the cloth, to tie round the lens and across the body. A useful device for simplify ing the operation of focussing and render ing a cloth unnecessary is shown by Fig. 634. It consists of a tube or chamber of velvet, arranged to fasten to the camera back while focussing, the other end terminating in a smaller opening just large enough to come over the eyes, and pro vided with a couple of elastic loops to go over the ears. A focussing glass or
magnifier is often of great assistance, be lost sight of, and is obviously an advantage. With lenses of high-grade definition very little stopping-down is ad visable for this class of work. A greater amount of brightness and relief, and a better rendering of atmosphere, are ob tained by the use of a large aperture. For further information concerning lenses, the reader is referred to the section deal ing with that subject.
especially if the light, is not very good, or if fine detail is required in certain parts of the picture. Fig. 635 shows a fixed focus pattern of magnifier, and Fig. 636 one with a sliding tube allowing adjust ment of focus.