Two tangents from any point are equally inclined to the focal distance of the point.
This is the only apparatus of this focal distance on the French coast.
One of the "first order" has a focal distance of 920 millimetres.
This effect, like the refractive power and focal distance, varies in degree in different diaphanous substances.
That of M. de Vilette was three feet eleven inches in diameter, and its focal distance was three feet two inches.
It had a focal distance of fifty-three feet, and an aperture of six feet.
For myself, I should care for nothing better than my Byrne five-inch of fifty-two inches' focal distance.
If O be brought nearer than the focal distance, the rays would diverge after passing through the lens.
The power is also defined as the ratio of the focal distance of the object glass to that of the eyepiece.
The entire interests of the colony were comprised within the focal distance of myopic vision.
focal distance n.
See focal length.
focal length n.
The distance from the surface of a lens or mirror to its focal point. Also called focal distance, focus.