This tower was designed for an elevation of 94 ft. to the focal plane.
The interference fringes formed in the focal plane are then viewed with an eyepiece of very high power, many thousand diameters.
He must have heard me in some way, and surely must have heard the purr of the focal plane shutter as I took his picture.
The total movement of the half-object glass is double the distance between the star images in the focal plane.
Rays of light from some distant object are converged by the objective (D) and form an inverted image (ab) at the focal plane (F).
If any error of convexity exists in the plate, the focal plane is disturbed, and the eyepiece must be moved out.
The photographer must change the plate, set the focal plane shutter, and press the release.
The focal plane of the light is elevated 93 ft. above high water.
The focal plane is at an elevation of 146 ft. above high water.
The focal plane is at a level of 158 ft. above high-water mark.
