36 Photography for the Sportsman Naturalist 



object, the greater must be the distance between 

 the lens and the plate in order to have the image 

 in sharp focus ; and when the distance between 

 the lens and the object is very short, say less than 

 two feet, a small deviation in the distance between 

 the lens and the plate suffices to entirely throw 

 the imao'e out of focus. Now, when the camera 

 is pointing downward at any upright object, such 

 as a growing flower or a bird's nest in a low bush, 

 as the camera must necessarily be tilted at a con- 

 siderable angle, it is obvious that the plate cannot 

 be parallel with the object if the back of the 

 camera is rigid ; and therefore if the top of the 

 object is in focus, the bottom, being much farther 

 away from the plate, will be out of focus, and vice 

 versa. This defect can be corrected, to a large 

 extent, by the proper use of the swing-back. It 

 also prevents distortion of lines, wdiich is bound 

 to occur when the plate and the object being 

 photographed are not parallel. This can best 

 be illustrated by focussing the camera upon a 

 tall building, where it is necessary to tilt the 

 instrument up in order to include the top of the 

 building. When this is done, it will be seen that 

 the lines of the building in the imasre converrre 

 at the top, giving it the appearance of falling over. 

 This is caused by the plate being tilted back, and 

 the lines can be straightened by the use of the 

 swing-back. If we ever try to use a camera that 



