ROVEMENTS IN COMPOUND LENSES SUITABLE FOR PHOTOGRAPHIC USES
Year: 1866

page_text: PROVISIONAL SPECIFICATION left by John Henry Dallmeyer at the
Office of the Commissioners of Patents, with his Petition, on the 18th
June 1866.
I, JOHN HENRY DALLMEYER, of 19, Bloomsbury Street, in the County of
Middlesex, Optician, do hereby declare the nature of the said Invention for
IMPROVEMENTS IN COMPOUND LENSES SUITABLE FOR PHOTOGRAPHIC USES," to be
as follows:-
In constructing photographic lenses suitable more especially for taking
views of architectural objects I employ a combination of three simple or
uncorrected lenses, two of which, viz., the first and third, are of crown or plate
glass and both positive, and the second or intermediate lens is of flint glass
and negative; these three lenses are positioned with intervals between them,
and a stop is placed between the intermediate and posterior (or the second
and third) lenses. Also 1 prefer to make the first or auterior lens larger than
the third or posterior leus, whereas heretofore in compound lenses in which the
anterior and posterior elements are both positive the posterior has usually
been made larger than the anterior, and never the reverse.
I prefer that the forms of the several simple lenses should be as follows:-
The first or anterior lens of crown glass is a deep concave meniscus, convex
side outside. The third or posterior lens of crown glass is plano-convex,
convex side outside, and the second or negative leus between these two is of
flint glass and plano-concave with the planeside facing the anterior lens; these
lenses are all made as thin as may be. The position of the stop for the cure
of distortion is in the optical centre of the combination.

page_text: In photographic lenses suitable especially for taking portrait pictures, and
which consists of two compound or corrected lenses with a space and stop
between them, it is also especially advantageous to make the anterior com-
pound lens larger than the posterior compound lens, whereas heretofore the
ordinary practice has been the reverse. Photographic lenses as at present
arranged, both those intended to take portrait pictures as well as landscape
pictures, are liable to what is for many purposes a defect, that is to say, they
give at one part of a picture representing one plane or distance from the lens
a painful and inartistic amount of detail, whilst in other parts representing
other planes or distances from the lens they, on the other hand, give less detail
than is desirable.
Now according to my Invention I correct this defect by mounting the
simple lenses or elements of the compound or combined lens in such manner,
that the operator can slightly alter the distance between the said elements,
and by this means the correction of the lens can be for the moment impaired
to any desired extent, so that then the focus in place of being at any defined
point is spread over a space more or less as desired, and then the definition of
the picture will no where be extremely sharp, nor on the other hand, will there
any where be any marked deficiency of detail. The simple elements of a
compound lens with which portrait or landscape pictures can be taken have
never heretofore been arranged so that the operator can alter at pleasure the
adjustment of the combination and thus produce the desired change of
aberration