ENLARGING WITHOUT A CONDENSER.
Very satisfactory results may be ob tained when the negatives are good and do not require dodging, but enlarging by such means is only a makeshift. The best plan is that shown in Fig. 436, where two lamps, A, are used to secure even illumination, and these lamps shine upon a sheet of cardboard, B, bent into circular form and held so by a thread, c. D is the camera. The exposure is of course con siderably longer than when a condenser is used, but if the lens works at fjG, it will not be very prolonged. Good work will be seen by reference to Fig. 435, the object of the condenser is to collect as . many rays as possible, and to cause them to converge and come to a point on the front lens. Further, the condenser and negative must he in such relationship to each other that the cone of light formed by the condenser just illuminates the margins of the negatives and no more. The form which the condenser must take to bring about this result, depends upon the direction of the rays or the character of the light being used. For example, Nv h en the rays are parallel, a simple convex lens will suffice to bring about the • desired result, always provided that the focal length of the condenser is equal to the focal length of the lens. When a con
denser is used with daylight it is employed merely to slim ten the exposure, and it is very rarely indeed, nowadays, that such is necessary. It is better for the condenser to be too long in focus than too short, for, whereas, when the distance between the condenser and the point of the cone of light is too great, this can generally be arranged for ; yet, on the other hand, if the cone is formed nearer than the lens may be placed, there is no remedy. This is one of the most important matters con cerning condensers, and is usually over looked. Although it is a matter of coin paratively little consequence in the optical lantern, yet, in enlarging, the annoyance of a condenser of too short focus is considerable, for in this work an image has to be produced of a set size. In the case of an ordinary illuminant, however, the rays are not parallel, but divergent, and require more. bending to bring them to a point. For this purpose, therefore. a more powerful lens or series of lenses must be employed, hence the reason for the form usually taken by the condenser as explained by Fig.