Marion and Co., compiler · London : Marion and Co. · leaf 173
169 VIGNETTING. the pasteboard. Now it is evident that if there be not plenty of light striking the frame obliquely, no rays will … pass beyond the edge of the aperture in the pasteboard. It is therefore necessary if, as sometimes happens, espe- cially in a town, a light from only a narrow portion of the sky can be obtained, to use tissue paper over the opening even when we are printing by diffused light. The effect of the…