1. The problem statement, all variables and given/known data You want to photograph a circular diffraction pattern whose central maximum has a diameter of 1.2cm . You have a helium-neon laser (λ=633nm) and a 0.13-mm-diameter pinhole. How far behind the pinhole should you place the viewing screen? 2. Relevant equations Y = λx/b Y=radius of central maximum b= slit diameter x=distance from screen 3. The attempt at a solution .012/2=633e-9*x/0.00013 x=1.23m <--- This answer is wrong. I don't know why.