516 HANDBOOK OF PHOTOGRAPHY 



Distortion Due to Film Shrinkage. 



1. Distinguishing Characteristics. — Shrinkage of film so that negative is not a 

 properly scaled image of the subject. 



2. CoMse.-^Swelling, expanding, and contraction of gelatin. 



3. Prevention. — Some swelling of the gelatin always takes place when it is wet. 

 Distortions to film expansion or contraction can be minimized by processing in solu- 

 tions, all of which are at the same temperature. In copying or process work where 

 slight distortions due to shrinkage are most serious, plates will be found preferable to 

 film. 



4. Remedy. — Xone. 



Distortion Due to Improper Monochromatic Rendition of Color. 



1. Distinguishing Characteristic. — In monochromatic photography, the brightness 

 of the gray image on the negative is not inversely proportional to the brilliance of the 

 colored image as evaluated by the human eye. This is sometimes difficult to deter- 

 mine in the negative but is usually apparent in a print, since the monochromatic 

 rendition of colors does not bear a close direct relation to the visual brilliance of the 

 corresponding part of the subject. 



2. Cause. — This defect may be due to any one or more of the following causes: 

 (a) use of orthonon (noncolor sensitive) or orthochromatic materials, which are 

 deficient in sensitivity for some regions of the visible spectrum ; (b) failure to use proper 

 light filters, or failure to use any filters whatsoever; (c) use of light source having such 

 spectral-energy distribution as to produce incorrect or undesired results with the type 

 of negative emulsion and filter employed. For a more complete discussion of this 

 subject, see chapter on Light Filters, page 312. 



3. Prevention. — The proper use of the correct type of negative emulsion, filter, 

 and light source to give the desired result. 



4. Remedy. — None, aside from retouching the negative or prmts made from it. 



Distortions Due to Lenses. 



1. Distinguishing Characteristic. — When the distortions of an image on the nega- 

 tive are due to distortions produced by the lens system, a wide variety of distinguishing 

 characteristics may be observed, depending upon the lens defect, or the improper use 

 and application of the optical system of the camera. The most common distinguishing 

 characteristics (although hardly common even in inexpensive cameras of good manu- 

 facture) are (a) same image does not appear identical when taken under conditions 

 identical in all respects except that the lens (and consequently the camera) is rotated 

 90° about its central or optical axis; (6) colored images are lacking in detail and sharp- 

 ness and are difficult to focus sharply on ground glass, although sharp focusing may be 

 obtained with monochromatic subjects; (c) images are curved, so as to give effect of 

 barrel or pincushion distortion which is especially objectionable when photographing 

 architectural subjects or copying line drawings; (d) distortion of bright point into a 

 pear-shaped image; (e) center of picture in focus, but outer edge out of fpcus, or vice 

 versa; (/) image cannot be sharply focused under any conditions with either colored 

 or monochromatic subject, and consequently fuzzy and unsharp negatives result; 

 (g) unequal illumination of field; {h) negative shows image in a circle, usually with 

 diffused edges. 



2. Cause. — These distortions are due, respectively, to: (a) astigmatism, (fe) 

 chromatic aberrations, (c) curvilinear distortion, {d) coma, (e) curvature of field, 

 (/) spherical aberrations or perhaps scratches in the lens, (g) probably due to lens 



