DEFECTS IN NEGATIVES AND PRINTS 515 



cameras having view finders at the edge of the camera and which are not corrected for 

 jjarallax. The condition will be most aggravated in photographing subjects near the 

 camera. If the perspective is poor, a lens of too long a focal length may have been 

 used for the conditions under which the print is to be viewed. If the^ perspective is 

 correct but the full subject is not included in the picture, the camera was placed too 

 close to the subject. The matter of perspective depends not only on the focal length 

 of the lens used, but also on the degree of enlargement and the normal viewing distance 

 of the print, (c) Improper perspective may be due to using lens of improper focal 

 length, improperly viewing the picture, or enlarging the picture so that when viewed 

 in the normal manner it does not present proper perspective, (d) Convergence of 

 vertical lines is often caused bj^ pointing the camera up at an angle in order to include 

 the top of the desired subject. This type of distortion is frequently encountered in 

 architectural photography where its effects are also most objectionable, (e) Too much 

 foreground results from pointing the camera down or, more usually, by not properly 

 raising the rising and falling front. Too little foreground results from the reverse 

 condition. (/) Lateral distortion, especially objectionable in portraiture, often results 

 from attempting to photograph a long object at an oblique angle. Relatively few view 

 cameras are provided with lateral swing backs, use of which would prevent this defect. 



3. Prevention. — (o) Bringing the camera closer to the subject and using lens of 

 proper focal length will assist in preventing these distortions. The focal length of 

 the lens should be approximately equal to the diagonal of the negative for good per- 

 spective. (6) Faulty pointing of the camera may be prevented by using a ground-glass 

 back for focusing. For the case of small cameras provided with a reflecting view finder 

 or wire iconoscope having no provision for correcting parallax, it is frequently possible 

 to obtain better results by focusing as well as possible with the view finder and then 

 correcting for parallax bj^ turning the camera slightly about a vertical axis through the 

 lens. Some experience is required to obtain the proper degree of shift, although judg- 

 ment of the proper shift is aided by sighting along the camera as close as possible along 

 the optical axis. A lens of shorter focal length or of wider angle will also allow more 

 of the subject to be included on the negative, although perspective considerations 

 must be given attention. Otherwise the camera should be removed farther from the 

 subject, (c) For prevention of incorrect perspective, see pages 26 and 94. {d) Con- 

 vergence of vertical lines can be prevented by making use of the swing back. Swinging 

 front, and rising front, if these adjustments are provided on the camera. The back of 

 the camera (or more strictly, the plane of the negative) should always be vertical when 

 making architectural photographs, to prevent distortions. The reason for this is one 

 of convention and in having become accustomed to artists' drawings, rather than one 

 of intrinsic correctness. It is also preferable that the axis of the lens be horizontal 

 when normal architectural subjects are photographed. The tops of tall buildings may 

 then be included by raising the rising front, and if this adjustment is insufficient, by 

 tilting the bed of the camera upward to further raise the lens with respect to the nega- 

 tive, (e) By raising the rising front, less foreground is included; by lowering the 

 front, more foreground may be included. (/) Lateral distortion may be prevented or 

 minimized by making use of the vertical tilt back, if the camera is provided with this 

 adjustment.. 



4. Remedy. — In general, there is no remedy for negatives containing the distortion 

 defects enumerated above, except retouching of the negative, or making a new photo- 

 graph under more desirable and correct conditions. In certain cases some forms of 

 distortion may be corrected or minimized in projection printing by tilting the bed of 

 the enlarger to compensate for distortion in the print. But while satisfactory in some 

 cases, such corrective measures are inferior to the results which might be obtained 

 from a negative originally without distortion. 



