Improvements in Photographic Objectives.
Year: 1893

page_text: Date of Application, 28th Feb., 1893-Accepted, 13th May, 1893
COMPLETE SPECIFICATION.
Improvements in Photographic Objectives.
I, ALBERT BARBER PARVIN, a citizen of the United States, residing at
No. 3213 Powelton Avenue, Philadelphia, in the County of Philadelphia and State
of Pennsylvania, Photographer, do hereby declare the nature and objects of my
invention for IMPROVEMENTS IN PHOTOGRAPHIC OBJECTIVES, and in what
manner the same is to be performed to be particularly described and ascertained
in and by the following statements:-
My invention has relation to photographic objectives which are adapted to
magnify the image of an object or objects at great distance, range, length or position
from the camera and with characteristic sharpness in detail.
It is generally understood by those skilled in photography that the size of the
image of an object upon the ground glass of a camera depends upon one of three
conditions; first, the focal length of the objective; second, the distance of the same
from the object to be photographed; and third, upon the size of the original. Two
of these conditions under certain circumstances are subject to variation, that is, the
distance from the object and the focus of the lens. Of course, if the object to be
photographed can be approached or lenses of different focal power are at hand, then
an image of the required size can be obtained, but such favourable conditions do not
exist in every day practice of the photographer. The required approach to the
desired object is often impossible or impracticable, because the required distance is
too great to afford recognizable detail in the resultant negative, requiring lenses of
extreme long focus, which necessarily are rather circumscribed. Suppose for
instance a photograph is required of an inscription upon a rock about three hundred
feet high, to obtain a fair view without distortion, the operative would have to locate
about seven hundred feet from the rock and this would bring the inscription about
eight hundred feet in a direct line from the lens. To secure distinctness or sharpness
as to detail, the letters of the inscription would have to appear at least four inches
high on the object in the resultant picture. To attain such a result say with a
lens of 5 x 6 meters focus, would require a camera with about an eighteen foot
extension. Then again small images with subsequent enlargement suffer from the
disadvantage of the grain of the plate for even by slight enlargement such is apt to
become so objectionably prominent as to destroy all detail. The efforts to over-
come such difficulty in exposure has suggested the use of a telescope, as a
substitute for a photographic objective, but such in practice was found to be
awkward and unstable; and moreover, with the use of the firmest tripod the
slightest breath of air or the least tremor was calculated to spoil the image of the
object.
The principal objects of my invention are first, to overcome the above mentioned
disadvantages and objectionable features and to provide a photographic objective of
comparatively simple construction and effective action for enlarging the image of an
object or objects at equal or unequal distances from each other with respect to the
position of the camera; second, to provide a photographic objective having a non-
extensible tube provided with a single negative lens ground according to a
mathematical formula to certain radii to a compound positive lens ground according
to a mathematical formula to different radii and the construction and arrangement
being such that the image of an object or objects at distant points or positions from
each other are appreciably enlarged or magnified with marked sharpness of detail
in the resultant negative or sensitive film or plate; third, to provide a photographic
objective with a non-extensible lens tube having a slit formed in the wall thereof
for the reception of a perforated slide or diaphragm for correcting marginal rays

page_text: and with a compound convergent positive lens and a divergent negative lens ; fourth,
to provide a photographic objective with a non-extensible tube having a convergent
compound-lens and a divergent single lens, respectively ground to different radii, and
the length of the lens tube being proportioned to the diameters of the lenses,
whereby increased magnification and sharpness of detail of the image of the distant
object with respect to its real location and position are obtained; fifth, to provide a
photographic objective with a tube having a double front lens of certain radii and a
single back lens of different radii; sixth, to provide a photographic objective with
a single divergent lens having each face or surface thereof of different radii ;
seventh, to provide a photographic objective with a convergent positive lens and
with a negative divergent lens having different radii in respect to the sides or
surfaces thereof; eighth, to provide a lens tube having two lenses, the radii of each
of which have a fixed relation with respect to the length of the tube; ninth, to
provide a photographic objective having a non-extensible tube with a concavo-
convex lens of certain radii of inside curves and of certain radii of outside curves to
afford certain focal length and a convexo-concave lens of certain radii adapted to
enlarge and to define with decided sharpness of detail the image of a distant object
transferred to a film or plate; and tenth, to provide a photographic objective
adapted to an ordinary camera and comprising a non-extensible tube provided with
a convergent compound or double lens and a divergent single lens and the radii of
said lenses with respect to each other being different on the respective faces or
surfaces thereof in order to give by the combination greatly increased magnification
or enlargement and great depth of focus.
My invention consists of a photographic objective comprising a tube having a
compound convergent lens and a single divergent lens suitably mounted therein.
My invention further consists of a photographic objective comprising a non-
extensible tube with convergent and divergent different radii lenses mounted
therein.
My invention further consists of a photographic objective comprising a non-
extensible tube provided with a double or compound convergent lens and with a
single divergent lens and respectively of different radii.
My invention further consists of a photographic objective having convergent
and divergent lenses of respectively different radii as to inside and outside curves,
faces or surfaces thereof, and adapted to greatly magnify or enlarge the image of
distant objects with sharpness of detail.
My invention further consists of a photographic objective, comprising a non-
extensible tube having a fixed relation to a compound lens of certain radii and to
a single lens of two different radii, the construction and arrangement thereof being
such, that the image of a distant object is greatly magnified and sharply defined,
so that the different positions of the objects are brought onto a film or plate with
characteristic sharpness and clearness of detail.
My invention further consists of a photographic objective comprising a small
tube provided with a compound lens of certain or fixed radii of inside and outside
faces, curves or surfaces and with a single lens of different radii of inside and
outside faces, curves or surfaces and the lenses respectively having convergent and
divergent properties in order to give great depth of focus and permit the image of
distant objects to be transferred in magnified form to a photographic film or plate
with characteristic sharpness as to detail and with remarkable clearness or
distinctiveness of field.
My invention further consists of a photographic objective provided with a non-
extensible tube having convergent and divergent lenses of certain or defined radii
with respect to each other and the length of the tube and susceptible of being
increased or decreased in length proportionately as the diameters of the respective
lenses are increased or diminished; and
My invention further consists of the improvements in photographic objectives
hereinafter described and claimed.
The nature and general characteristic features of my invention will be more

page_text: fully understood from the following description taken in connection with the
accompanying drawings forming part hereof; and in which
Figure 1, is a longitudinal central section through the photographic objective,
showing a non-extensible tube provided with a detachable perforated diaphragm or
slide adapted to correct marginal rays and with a concavo-convex positive lens and
with a convexo-concave negative lens, the latter embodying features of my invention;
and
Fig. 2, is a sectional view, showing in detail, with the tube removed, the com-
pound convergent positive lens, and the divergent negative lens of my invention,
and the lenses according to a mathematical formula ground respectively to different
radii on their inside and outside curves, surfaces or faces, in order to adapt the
same to the non-extensible tube of Fig. 1, of a length proportional to the diameters
of the respective lenses, whereby great depth of focus and enlargement of the
image of distant objects with characteristic sharpness in the transfer to a photograph
film or plate are ensured.
<<
Referring to the drawings A, is a brass or other tube provided with a barrel a,
and with detachable threaded coupling rings and sleeves b, b¹, b, c, c' and c³, for
supporting in proper position in the barrel a, the respective lenses B and C. About
midway of the barrel of the tube A, and between the lenses B and C, is provided
a slit d, adapted for the insertion of a detachable perforated diaphragm or slide e,
for correcting marginal rays. The tube A, is provided in the front extremity
thereof, with a compound lens B, ground according to a mathematical formula
with respect to the inside and outside curves, faces or surfaces thereof, to certain
radii and at the rear extremity of the barrel of the tube A, is mounted a single
lens C, ground according to a mathematical formula as to inside and outside
curves, surfaces or faces, to different radii. The tube A, with the lenses B and C,
constitutes what is generally known as a photographic objective." The tube A,
for a 5 x 7 or 5 x 8 plate or sensitized film may be about two and one
quarter inches in length to lenses each about one and one quarter inches
diameter. It should be borne in mind, however, that as the tube is increased
or diminished in length, so proportionately the diameters of the lenses, will
be increased or diminished. With respect to the lenses, it may be remarked,
that the main feature of this invention is to provide a single lens ground according
to a mathematical formula on the inside and outside curves, faces or surfaces to
certain radii and of a compound lens of certain other radii, as to the inside and
outside curves, faces or surfaces thereof. Moreover, these lenses mounted in the
tube A, have respectively convergent and divergent proclivities and are adapted
to give greatly enlarged image of the distant object, that is to say, to the extent
of ten, twenty and even a hundred-fold without impairing in the least any of the
characteristic sharpness of detail embraced within the field of the objective.
Moreover, the image of the distant objects transferred to the sensitized film or
plate and in the resultant picture according to my invention, is much more
pronounced than heretofore was possible by the use of any of the commercial
camera objectives. The negative single lens C, mounted in the tube A, is ground
on the faces or surfaces thereof, to different radii and is used in connection with
the compound or double positive lens ground to different radii, in lieu of the
generally employed compound lenses for such purposes. Furthermore, the positive
lens is a convergent one, while the negative is a divergent lens. By providing
the non-extensible tube A, with respectively convergent and divergent lenses, it
has been found that great depth of focus is obtained, as well as magnification or
enlargement of the image of distant objects, without in the least losing any of the
characteristic detail required.
In order that my invention may be fully understood by those skilled in optics and
in the art of photography, the relation which the back lens C bears to the front
lens B, will now be given.
The front compound lens comprises preferably a double convex lens ground
respectively to the radii of 2 and 13 inches, more or less, to outside curve, face

page_text: or surface thereof, and with a double concave lens ground respectively to the radii
of 1 and 31 inches, more or less, to inside curve, face or surface, and as so
combined such compound lens has a focal length of 6 inches, more or less.
The back or single lens may be a convexo-concave or periscopic lens ground to
the radii of 25 inches, more or less, to the outside face or surface thereof and
ground to the radii of 44 inches, more or less, to the inside face or surface and this
lens has a focal length of 5 inches, more or less.
The above combination of lenses mounted in the tube having a length of
about 2 inches, may be applied to any ordinary commercial camera and will give
a depth of focus of about 20 inches, more or less
In the practice of my invention with a photographic objective constructed as
described, images of objects have been taken at 6600 feet to two miles distant from
the camera with greater sharpness of detail in the prints than ordinarily can be
obtained in prints taken at 100 feet distant from the camera.
The foregoing
advantageous features of my invention are due to the character of lenses employed
in the non-extensible tube and to the depth of focus obtained from the use thereof.
In the practice of my invention neither spherical aberration nor astigmatism is
present, so that the objective is achromatic.
Having now particularly described and ascertained the nature and objects of my
invention and in what manner the same is to be performed, I declare that what I
claim is :-
:-
1. A photographic objective comprising a tube provided with a convergent front
lens and a divergent rear lens, the construction being such that great depth of
focus is obtained and enlargement of the image of a distant object ensured in its
transfer onto a sensitized film or plate, substantially as described.
2. A photographic objective comprising a non-extensible tube provided with a
compound front lens and a single rear lens of different radii with respect to each
other, substantially as and for the purposes described.
3. A photographic objective comprising a non-extensible tube provided with a
detachable diaphragm or slide, a compound front lens of certain radii and a single
rear lens of different radii, substantially as and for the purposes described.
4. A photographic objective comprising a non-extensible tube provided with a
detachable perforated slide or diaphragm, a compound convergent front lens and a
single divergent rear lens of different radii in respect to the faces or surfaces and
of different focal length, whereby great magnification or enlargement of the image
of a distant object is ensured with characteristic sharpness of detail, substantially
as described.
5. A photographic objective provided with a divergent rear lens having faces or
surfaces of different radii, substantially as and for the purposes described.
6. A photographic objective comprising a non-extensible tube provided with a
detachable perforated slide or diaphragm, a single convexo-concave rear lens of
certain radii as to inside and outside faces or surfaces and a compound front lens of
certain radii as to inside and outside faces or surfaces, substantially as and for the
purposes described.
7. A photographic objective comprising a non-extensible tube provided with a
compound front convergent lens and a single divergent lens respectively of different
focal length, substantially as and for the purposes described.
8. A photographic objective comprising a non-extensible tube with a detachable
perforated diaphragm, a compound front lens and a periscopic rear lens, substantially
as and for the purposes described.
9. A photographic objective comprising a non-extensible tube provided with a
compound front lens of certain radii and a single rear lens of certain radii,
substantially as and for the purposes described.
10. A photographic objective comprising a non-extensible tube provided with a
compound concavo-convex convergent front lens, and a single convexo-concave
divergent rear lens, substantially as and for the purposes described.

page_text: 11. A photographic objective comprising a non-extensible tube having a
compound front convex-concavo lens and a single periscopic rear lens, the arrange-
ment being such that great depth of focus is obtained and the transfer of the image
of distant objects embraced within the field to a sensitized film or plate is ensured
with great magnification and with characteristic sharpness of detail, substantially
as described.
ALBERT BARBER PARVIN.
W. P. Thompson & Boult,
Agents for the Applicant.