These rays come to a focus at a point F lying in the focal plane of the telescope.
The interference fringes formed in the focal plane are then viewed with an eyepiece of very high power, many thousand diameters.
The focal plane is at an elevation of 146 ft. above high water.
If any error of convexity exists in the plate, the focal plane is disturbed, and the eyepiece must be moved out.
Rays of light from some distant object are converged by the objective (D) and form an inverted image (ab) at the focal plane (F).
The photographer must change the plate, set the focal plane shutter, and press the release.
What is seen through the eye-piece in any case is the same as would be depicted upon a screen in the focal plane.
The focal plane of the light is at an elevation of 109 ft. above high water.
The focal plane is at a level of 158 ft. above high-water mark.
The focal plane of the light is elevated 120 ft. above high water.