PHOTOGRAPHIC LENSES
Year: 1877

page_text: PROVISIONAL SPECIFICATION left by the said Frederick von Voigtländer at
the Office of the Commissioners of Patents on the 17th May 1877.
FREDERICK VON VOIGTLÄNDER, of Brunswick, Germany.
PHOTOGRAPHIC LENSES."
"IMPROVEMENTS IN
>
This Invention has for its object improvements in photographic lenses applicable
especially for groups, landscapes, and reproductions.
For this purpose I construct the lens so as to be over corrected and somewhat
imperfect for the visual picture, in order to obtain the chemical picture as perfect
as possible; this I am enabled to do by making one of the glasses of each lens of a
symmetrical double combination lens from a glass of greater density than has ever
before been used in the manufacture of photographic lenses.
By forming a photographic lens in the manner above described I am also enabled
to obtain an extremely short focus with reference to size of aperture, that is, as
compared with lenses heretofore used for. similar purposes; also a depth of focus
not obtainable by any previous construction of lens, and great illuminating power.
The lens also can be used with an extremely short distance between itself and the
object.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed by
the said Frederick von Voigtländer in the Great Seal Patent Office on the 17th
November 1877.
FREDERICK VON VOIGTLÄNDER, of Brunswick, Germany.
PHOTOGRAPHIC LENSES."
"IMPROVEMENTS IN
This Invention has for its object improvements in symmetrical lenses for photo-
graphic purposes.
Symmetrical photographic lenses constructed according to my Invention possess a
considerably greater illuminating power and greater depth of focus than any other
of the existing symmetrical constructions. These advantages have been obtained by
the peculiarity of their construction, founded on calculations, but especially by the
adoption and application of an optical principle not considered hitherto.
In every photographic lens two different kinds of rays come into action, viz., the
optical or visual rays, and the chemical (not visual) rays; and from this point of
view, also two different pictures are obtained, viz., the optical or visual and the
chemical picture.
In all photographic leuses hitherto constructed, the optical picture was treated
upon the same principles as the chemical; but as both kinds of rays have evident
differences regarding their action, it has been my study and endeavour to make
the chemical picture, which in fact is the only one coming into operation when
making a photograph, as perfect as possible even by somewhat injuring the visual
picture.
I have fully succeeded in this respect by employing as material a flint glass of
very great specific gravity and great refracting power, such as has never been used
before for photographic lenses. By this means I am enabled to over correct the
visual picture, that is, give an overplus to the blue spectral rays; thus the chemical
picture (the useful one in photography) is brought to that perfection which my new
lenses possess.. Also by this same means I am enabled to shorten the combined
focus of this construction, so as even to obtain a proportion of six to one between
the focus and aperture, and from this important circumstance, according to the laws of
optics, the lenses derive great illuminating power.
The Drawing represents a vertical section of symmetrical photographic lens
constructed according to my Invention. It consists of two exactly symmetrical
object glasses both object glasses are exactly identical, and consist each of two
lenses (meniseses); the object glasses are so placed that the concave sides face each
other. The lens A consists of heavy flint glass, the index of refracture being=1'655;
of the other, B, the refracting index is=1.55.
The combined focal length of such a system being supposed to be = 1.000.
The aperture of the object glasses is = 0.066.

page_text: as may be, and also to obtain a considerably increased illuminating power with great
depth of focus, substantially as above described.
Second. The construction of symmetrical lenses for photographic uses with the
parts formed of the densities and curvatures, substantially as above described.
In witness whereof, I, the said Frederick von Voigtländer have hereunto set
my hand and seal, this Eighth day of November, in the year of our Lord One
thousand eight hundred and seventy-seven.
FK. V. VOIGTLANDER. (L.S.)