I could vary the focal point from a few feet to several miles.
Instead, there are two focal points, called the foci, as you will see presently.
This would also be about the focal length of the finished lens.
Toward a focal point: from the east, two people; from the north, two people.
It is naturally the focal point of the trade between Europe and Asia.
They still respond to the activities which are centered in the focal neighborhood.
B is a double convex lens, which has a focal length of twenty inches.
It should not be forgotten that it is, in a sense, the focal centre of the room.
Its focal length of 30 feet can be increased to 108 feet by a Cassegrainian combination.
This tower was designed for an elevation of 94 ft. to the focal plane.
