With regard to the lens required, the practice adhered to by most photographers is to use a lens having a focal length equal to the diagonal of the plate used.
The result was a Newtonian of exquisite definition, with an aperture of two, and a focal length of twenty feet, provided by a novel artifice with the equatoreal mounting, previously regarded as available only for refractors.
Focal length, aperture and image angle are the chief details concerning lenses, granting that the aberrations referred to above are satisfactorily corrected.
In England a lens which will cover with a large stop, say f/8, is a desideratum, but in the Alps it is very rarely that such a large ratio of aperture to focal length is required.
When the simple expression "focal length" is used, it always refers to the equivalent focal length.
This point is thus known as the principal focus of the lens, and the distance between this point and the lens is called the focal length of the lens.
This point is known as the principal focus of the mirror, and the distance between it and the mirror is called the focal length of the mirror.
To find length of throw needed to obtain a certain size of picture: Multiply required picture dimension by focal length of lens and divide by slide or film dimension.
There is no very accurate relation necessary between the focal length of condenser and objective.
The glass is a lens of short focus, held at a distance somewhat less than its principal focal length, F (see Fig.
What is meant by the focus or focal length of a lens?
The principal instruments purchased therewith were a mural quadrant and a transit instrument, both eight feet in focal length, still preserved on the walls of the transit-room.
The above list will hopefully provide you with a few useful examples demonstrating the appropriate usage of "focal length" in a variety of sentences. We hope that you will now be able to make sentences using this group of words.
