Observations on Photographic Appliances and their Uses. 259 



to be better for general landscapes and views than any other lens, 

 as it gives more brilliant results, owing to its non-correction for 

 barrel distortion, and partly, also, because the rays of light have a 

 smaller number of lenses to go through. They are cheap, and 

 every outdoor photographer should be the owner of at least one 

 of them. 



The rectilinear lenses most in use and in the market include a 

 very wide angle lens and one whose angle corresponds nearly with 

 the angle which an artist uses when painting outdoor views, land- 

 scapes, etc. 



A lens is said to be reclihnear when it reproduces straight lines 

 conectly. Therefore, a rectilinear lens must give the true per- 

 spective as seen from the point of view occupied by the camera at 

 the time of exposure. Wide angle lenses are specially useful when 

 making views of interiors and confined situations, but for short 

 exposure and instantaneous views more especially they are not so 

 well adapted as the other double combination, as they have not 

 more than one-half their rapidity. 



In order to get a good perspective effect and throw out a lot 

 of uninteresting details on a picture, a lens should have a focal 

 length at least eipial to the greatest dimension of the plate, and a 

 better result is obtained if the focal length exceeds ^this greatest 

 dimension by from twenty to thirty per cent. 



Whenever a short focus lens is used to cover a large plate, 

 it oftei' brings in more details than are wanted, the perspective is 

 painfully violent, objects in the distance appearing much further 

 away than they really are. 



All lenses are supplied with a set of diaphragms or stops, 

 which are intended to correct their spherical aberration, and 

 increase their depth of focus, the larger stops being intended for 

 portrait and instantaneous work where it is necessary to sacrifice 

 definition at the edges of the field in order to gain rapidity, the 

 smaller ones used for time exposures and where sharp definition is 

 required to the very edges. 



In comparing lenses of the same focal length the one which, 

 with a stop of the same diameter, gives the best definition and 

 shows greater depth of focus, is generally the best, provided it be 

 not defective in some other way. 



A first-class rectilinear lens (leaving out wide angle) should, 

 with a stop corresponding to U. S. No. 16, give a fair definition 



