Angular aperture

<p>The angular aperture 
  
    
      
        a
      
    
    {\displaystyle a}
  
 of a <a href="/facts/Lens_(optics)/ejlH6n5c">lens</a> is the <a href="/facts/Angular_size/p2xv4vcQ">angular size</a> of the lens <a href="/facts/Aperture/8PV11GQm">aperture</a> as seen from the <a href="/facts/Focus_(optics)/QuRKfhg6">focal point</a>:
</p>

a
        =
        2
        arctan
        ⁡
        
          (
          
            
              
                D
                
                  /
                
                2
              
              f
            
          
          )
        
        =
        2
        arctan
        ⁡
        
          (
          
            
              D
              
                2
                f
              
            
          
          )
        
      
    
    {\displaystyle a=2\arctan \left({\frac {D/2}{f}}\right)=2\arctan \left({\frac {D}{2f}}\right)}

<p>where 
</p>

f
      
    
    {\displaystyle f}
  
 is the <a href="/facts/Focal_length/brGIUkEY">focal length</a>

D
      
    
    {\displaystyle D}
  
 is the <a href="/facts/Diameter/6uNn4VmU">diameter</a> of the <a href="/facts/Aperture/8PV11GQm">aperture</a>.

Angular aperture open-in-new

Angular aperture