Those rays of light which are traversing a parallel course, when they enter the lens are brought to a focus nearer the lens than others.

Hence the difficulty the operator sometimes experiences by not being able to "obtain a focus," when he wishes to secure a picture of some very distant objects; he does not get his ground glass near enough to the lenses.

Again, the rays from an object near by may be termed diverging rays.

This will be better comprehended by reference to Fig.

9, where it will be seen that the dotted lines, representing parallel rays, meet nearer the lenses than those from the point A.The closer the object is to the lenses, the greater will be the divergence.