42 Photography for the Sportsman Naturalist 



different apertures. If he would learn more 

 about it, and know exactly how each system is 

 worked out, he can find it in one of the books on 

 lenses of which I have already spoken. 



The angle of view of a lens is the diameter of 

 the field that is sharply covered by that lens. 

 There are narrow, medium, and wide angle 

 lenses. The greater the focal length of a lens 

 compared with the size of the plate the narrower 

 the angle, but as any lens which will cover a 

 large plate will cover a smaller one — the greater 

 includes the less — and as many lenses when 

 stopped clown will cover a much larger plate than 

 when at full opening, there is only one way in 

 which we can call lenses wide or narrow angle. 

 There are lenses which will only cover a plate at 

 a certain narrow angle, and stopping down does 

 not extend their fields. They are rightly called 

 narrow angle lenses. There are other lenses 

 which will work at a very wide angle, covering 

 a plate sharply from corner to corner at an angle 

 of ninety degrees and even more. All lenses will 

 not do this, and therefore those that will are cor- 

 rectly called wide angle. To a nature worker a 

 wide angle lens is seldom necessary, although 

 sometimes extremely useful. 



In choosing a lens for nature work we must 

 be governed principally by two considerations: 

 speed and focal length. Lenses vary in price 



