THE ordinary hand camera has this very serious disadvantage, that the actual image, which is about to be imprinted on the sensitive plate, cannot be seen by the operator. He is obliged to take it for granted, and estimate its actual qualities from the view-finder. Thus he has less facility for the composition of his picture, and loses the means of gauging the exposure by the comparative degree of illumination which the plate will receive. To meet these difficulties the twin-lens camera was invented, consisting of two lenses in two separate chambers superposed, the upper of which was used as a guide in focussing; and afterwards the reflex camera.
As its distinctive feature, a reflex camera is fitted with a hinged mirror crossing the body near the plate at an angle of about 45°, and reflecting the image in exactly the same focus as the plate on to a ground-glass screen at the top. Incidentally the image thus appears in its true direction, and not upside down, as on the ordinary focussing-screen. The screen is shaded from direct light by a more or less prominent hood. Early patterns of reflex camera were of exceedingly simple design, and one of these has survived to the present day - Messrs. Watson's Vanneck. In this instrument the mirror itself acts as the shutter. There are theoretic objections to a shutter working at such a distance from the plate, but for the moderate speeds (from 1/10 to 1/90 sec.) the Vanneck shutter does its duty very well. We used a Vanneck for some years, and had no fault to find with it except the plate-changing arrangement; and if it could only be fitted with dark slides we believe the Vanneck would still have a long and honourable career before it.
We referred to this difficulty in the last chapter. It is often very troublesome to have to estimate the exact distance of the predominating feature in the view, and still more troublesome to remember the calculations with regard to the relative sharpness of other objects nearer or further from the lens, which form integral features in the composition. All this is obviated with a reflex camera. We see the actual view before us on the focussing screen, and can adjust the focus and the stop in the lens to produce the desired effect as accurately as if we were working with a stand camera.
Here the above advantage is presented in more accentuated form. The figure within a few feet of the lens needs to be focussed to a nicety. The actual size of the features is seen, and not guessed at from the view-finder. But this is not all. Working with a large stop so near the lens, the background is necessarily thrown out of focus. A hand-camera portrait too often betrays its origin by the eccentric manner in which the circles of confusion, formed by the shadow of some distant object, enter into competition with the features or hair of the individual. When the portrait is focussed in a reflex there is some chance that the distracting elements will be observed and avoided.
Here again the reflex camera insures the operator against mistakes. We may fit the hand camera with separate scales for the wide-angle, rectilinear, and single combination. Only too well we know what a tax is put upon human frailty. Aliquando nutat Homerus. And the reflex lends itself to the occasional adoption of very long-focus lenses, which combine high rapidity with the greater pictorial possibilities inherent in views of this kind. To these we may add that the whole view is seen, no matter how much the front is raised or swung. When taking pictures in an ancient town the tourist often shrinks from setting up the stand. He knows too well that his act would be a signal for an admiring and inquisitive crowd to assemble, and even to pose themselves in the very midst of his view. Yet he is puzzled to decide whether his rising front will cut off too much foreground, or fail to reach the quaint gable-ends that he is bent on including.
The chief objection urged against the reflex camera is that, owing to the length of hood, it must be manipulated at a very low level to enable the operator to follow the image on the screen, much lower than an ordinary hand camera, and therefore that most pictures will contain too much foreground. On the other hand, the rising front is available. At any athletic sports meeting press photographers may be seen holding their cameras upside down above their heads and following the image through the hood with perfect equanimity. The modern simplified pattern of shutter, which adjusts exposure with a single movement, provides for this method.
The reflex camera is the only one with which satisfactory pictures can be obtained of animals at play, birds in the garden or in the woods, and wild nature generally. In this special field the benefits of visible focus and power to employ long-focus lenses react on one another. By the aid of the latter fair-sized pictures are possible at a distance sufficient to escape the observation of these nervous and bashful subjects.
Moving objects up to a certain speed come within the province of the ordinary stand camera, that is, if they can be focussed for in advance, and are bound to pass over a fixed spot, as, for instance, an express train, a coach, or, to a certain extent, the competitors in a cycle or motor race. The hand camera may by good luck succeed, if fitted with a reliable shutter. But the reflex camera is now recognised as the instrument fulfilling the conditions involved in the most satisfactory manner.
The one great problem involved in taking instantaneous photographs - and it applies to a less extent to those taken by the previously set-up stand camera - is the capacity of ensuring that the shutter shall act at the psychological moment; for the best-devised shutter in the world takes a fraction of a second to respond to the press of the button. With an express train, a bird rising in flight, or a cricket bat, a very small error, say, 1/50 sec, may rob the plate of all value as a record. The personal equation comes into value here. Constant training of eye and nerve will create the faculty of anticipating, by just the right interval of time, the instant when the moving object will reach the most favourable point. After some practice this faculty will become automatic. Owing to the double character of the mechanism of a high-class reflex camera, in which the mirror catch has to act simultaneously with the shutter-release, the interval is probably rather longer, but none the less may be anticipated quite accurately by the individual.