EXPOSURE IN THE CAMERA.
ON removing the excited plate from the bath, it is at its maximum of sensibility, and should be exposed as quickly as possible in the camera; and as the sensibility rapidly deteriorates by being allowed to drain, the adjustment of the focus, and any other arrangement the apparatus may require, should be attended to while the plate is iodizing, to prevent, as much as possible, loss of sensibility.
No certain measure of time can be given for exposing the plate, for so many influences are at work to modify and control the time. The sensibility of the collodion, the strength of the developing solution, the power of the lens, and the intensity of the light, all have to be calculated in deciding on the requisite time; consequently, the experience gained by practice will be the operator's best and surest guide.
I may remark, however, that for a positive on glass, less exposure is necessary than for a negative drawing; the latter will generally require about one-third longer time. The indications of over exposure are, a too rapid development of the image, and a general indistinctness over the whole surface. When the picture is brought out with too much celerity, an uneven development is almost sure to result, from parts of the picture appearing before the developing liquid has had time to cover the plates; consequently, less exposure in the next trial is the obvious remedy for the evil.
With too little exposure to light, the image is slow in developing, the solution on the plate begins to decompose and become useless, the image produced is faint and indistinct, or there is too great a contrast between light and shade ; and if the operation is continued for any length of time, in the hopes that a picture may eventually be produced, a deposit is likely to form upon the plate, interfering very much with the distinctness of the delicate parts. It is necessary, before exposing the plate in the camera, to decide whether a positive or a negative picture is required, in order to vary the time of exposure accordingly.
Very often from the brightness of the light, or a miscalculation of time, the positive picture will develope with great rapidity, barely giving time to cover the plate before it is finished, and requires fixing; if when developing you find you have overstepped the right time of exposure, and there appears little hopes of procuring a clear and distinct positive, let the development continue for a negative; it is better to do this than to halt within the two, to find that a little less or a little more development would have been better for the one or the other kind of picture.
Care should be taken to place the camera horizontal to the object to be taken, otherwise upright lines in the picture will fall inwards, and have an unpleasant effect, and interfere very much with the truthfulness of the picture. If the image cannot be got on the focussing glass, as it is desired, the lens should be raised or lowered on the sliding front, to meet the difficulty.
With a landscape in which there is foreground, middle distance, and very distant object, it will be found best to focus distinctly the middle distance. If the lens is good, and the spot not too large, the two extremes will generally come sufficiently distinct. It will be better, however, that the foreground should be a little out of focus if the adjustment cannot be made perfect for all distances. When all the parts and all distances in a picture are equally sharp and distinct, an unpleasant effect is likely to be produced, not at all artistic or pleasing to the eye.
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