EXPOSURE, INCORRECT Correct exposure is the basis of all successful work in photography. But in some subjects, especially those with moving objects or very dark interiors, it may be impossible to expose sufficiently long ; and occasionally errors of judgment may lead to both under- and over exposed plates.
Incorrectly exposed plates tan always be more successfully treated if the error is known before development is begun than if it is only recognised when the operation has made considerable pro gress. Under-exposure is the more difficult to treat, as there is insufficient light-action. If the subject is one that is deficient in contrast, or exposed in a dull light, the best method is prolonged development either in a normal solu tion, or in one containing the normal amount of developing reagent and excess of alkali. If the subject is strong in its contrasts of light and shade, prolonged treatment in a normal solution considerably diluted, or in a diluted solution with extra alkali added, is the only satisfactory method. The diluted solution lessens contrasts considerably ; and it allows prolonged develop ment without obtaining much strength in the light tones. Detail is obtained without density, and greater softness results than can be obtained by any other method. If the resultant negative is still too harsh, the methods given under the headings " Hard Negatives," " Harmonising Con trasts," etc., must be adopted.
Over-exposure within moderate limits comes within the latitude of the plate (see " Latitude in Plates "), and requires no special treatment, provided that the subject is one of good con trast of light and shade. If a plate has received an exposure from one and a-half times to twice the normal amount, development may be normal ; and though the plate will look very strong, and different from one that has been correctly exposed, the resultant print will be little, if any, inferior to that yielded by a normally exposed plate. The time of printing will be much longer, and that will be the only difference. In moder ate over-exposure in subjects deficient in con trast, for copying, etc., the only efficient means of correcting over-exposure in development is by treating it throughout by a modified solution. Potassium bromide may be added to a normal developer in any quantity up to 2 grs. to each r oz. of solution or a more concentrated developer may be employed, and 3 grs. or 4 grs. of bromide added to each r oz.
Another method of working is to develop either with a normal or a concentrated solution until the extreme shadows begin to veil ; then stop development and fix the plate, afterwards intensifying to bring it to full printing strength.