The American annual of photography . s a picture formed to belacking in contrast, and of a milky appearance. Distortion, another defect, often due to the single lens, is oftwo kinds, positive and negative. Positive distortion is causedby the diaphragm being placed in front of the lens, and causesthe straight lines to be shown bowed out, or barrel distortion is caused by the diaphragm being placedon the back of the lens and this makes straight lines appear tobe concave, or have a pincushion effect. 38 Distortion of one kind or another is bound to occur in asingle lens, and it ha
The American annual of photography . s a picture formed to belacking in contrast, and of a milky appearance. Distortion, another defect, often due to the single lens, is oftwo kinds, positive and negative. Positive distortion is causedby the diaphragm being placed in front of the lens, and causesthe straight lines to be shown bowed out, or barrel distortion is caused by the diaphragm being placedon the back of the lens and this makes straight lines appear tobe concave, or have a pincushion effect. 38 Distortion of one kind or another is bound to occur in asingle lens, and it has been found that for most work it ispreferable to have the barrel shape, or positive form, whichresults from having the diaphragm in front of the lens. It isoften the case that when a lens shows excessive distortion thata considerable part of this may be corrected by adjusting thedistance between the lens and diaphragm. Distortion in eitlierform is most apparent near the edges of the plate, and stop-ping down does not eliminate HARVEST DAYS. WM. T. KNOX. 39
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