how do i select a fan angle for laser lines?

 The fan angle of a laser line specifies the angular spread of the laser beam at a particular distance. The length of the line (L) produced at a certain projection distance (D) is given by the formula L=2Dtan(q/2);where q is the fan angle. We have line lasers available with fan angles of 4, 15, 30, 45, 60, 75 and 90 degrees.

 The width of the lens fan angle is a function of the refractive index of the glass and the roof angle. The steeper the roof and the higher the refractive index, the wider the fan angle and the longer the line for a given projection distance. Small fan angles typically use optical glass of a moderate, n=1.5, refractive index. Large fan angles are best made with a high index glass, n= 1.8, or higher to minimize the roof's otherwise steep angle.