A method of and apparatus for monitoring the method comprising the steps of: generating electromagnetic radiation; using a first lens to form the electromagnetic radiation into a beam; directing the beam through a sampling volume for impingement upon the fibers; positioning a second lens in the same horizontal plane as the first lens such that the angle, whose tangent is D/d, is greater than or equal to five degrees, where D is the diameter of the second lens and d is the distance from a plane through the center of the second lens to the center of the sampling volume; collecting electromagnetic radiation backscattered from the fibers by means of the second lens; and generating a signal responsive to the amount of radiation collected as an indication of the average diameter of the fibers.