Text books often define the Raleigh Criterea as Sin(theta) = 1.22* Lambda/D   
      
   Should not the criterea be,  TAN(theta) = 1.22 * Lambda/D   
      
   I am suggesting the criterea should be with tan from looking at its derivation   
   from Bessel function   
      
   r = 3.832/pi    *    L*Lambda/D  to first point   
   r =   1.22      *    L*Lambda/D   
   r/L = 1.22      *      lambda/D   
   tan (theta) = r/L = 1.22 * Lambda/D   
      
   if i could draw a picture of r and L, that would be great, but I will have to   
   draw it with words.  I am assuming r is the distance between the edge of the   
   aires disc to the center (its radius) and the L is the focal length which is   
   the triangle side    
   which forms a right angle with the radius. the hypotenuse is not directly   
   defined; hence the application of tan and not sin which requires knowing the   
   hypotenuse value.   
      
   I appreciate that if the angle is small, then sin(theta) = tan(theta)   
   some people say sin(theta) can equal theta but I can not see that.   
      
   sin (1E-5) = 1.745E-7 degrees   
   tan (1E-5) = 1.745E-7 degrees   
   but 1E-5 does not equal 1.245E-7   
       
   Please help me understand. I truly am in the space of trying to understand.   
      
   Thank you   
   bil   
      
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