An Improved Adjustment for Photographic Objectives.
Year: 1890

page_text: Date of Application, 29th Nov., 1890-Accepted, 3rd Jan., 1891
COMPLETE SPECIFICATION.
An Improved Adjustment for Photographic Objectives.
I, ERNST GUNDLACH, of 112 South Ave., Rochester, State of New York, U.S.A.,
Inventor, do hereby declare the nature of this invention and in what manner the
same is to be performed, to be particularly described and ascertained in and by the
following statement :—
My invention relates to such photographic objectives or lenses which are to be used
with different openings or diaphragms according to light, distance of object, angle of
field and other circumstances. Such objectives are most generally composed of two
achromatic lenses which are mounted rigidly on to the ends of a tube, and in such a
distance from each other as is most favorable to the special purpose of the objective,
the diaphragm being situated about midways between the lenses.
Such most favourable distance of the lenses, however, varies considerably with the
diameter or opening of the diaphragm used, and also with the angle of field to be
embraced by the objective. For instance, in landscape lenses, which require a wide
angle of field and are mostly used with small diaphraguis, the best photographic result
is obtained with a comparatively short distance of the lenses from each other or from
the diaphragm, while in portrait lenses, which have a much smaller angle of field, but
are generally required to work with comparatively wide openings or large diaphragms,
the distance of the lenses is to be correspondingly great, in order to produce the least
possible focal distortion at or near the edges of the picture.
In fact, if the distance of the lenses is so regulated that the objective will with
a small diaphragm produce the best possible picture, it will work very unsatisfactory
with a large diaphragm, producing a curved field and much distortion at the sides.
If, however the lenses are brought farther apart, so as to have the most favourable
position for a large diaphragm, then the picture produced with such will certainly
show considerable improvement while, on the other hand, it would then be much
inferior if a small diaphragm were used.
A similar relation exists between the angle of field and the distance of the lenses.
The wider an angle the objective is to embrace, the nearer the lenses must be brought
together or to the diaphragın not for the immediate purpose of widening or increasing
the angle of said objective, as is actually done thereby, to some extent; but to reduce
the distortion at the sides, and the aberrations in the flatness of the field, which
certainly increase with the angle. Thus a short distance of the lenses will adjust the
objective for small diaphragm and wide angle, and a long distance for large diaphragm
and narrow angle at the same time.
Furthermore, if the object is very near to the objective and the diaphragm of the
latter is large, as is for instance generally the case with the portrait objective, then
the proper or most favourable distance of the lenses of the objective also varies
considerably with the distance of the object, and still more with the difference of
the distances of different parts of the object, if those parts forming the center of the
picture have another distance than those near the edges. If, for instance, a person
is to be taken in a sitting position, the hands are usually much nearer to the objective
than the face and consequently, if the image of the latter appears sharply defined on
the focusing screen, the bands will be out of focus, the latter being too long and lying
behind the plane of the image. Provided then, the image of the hands to he near
the edge and the face at or near the center of the picture, the defect could be remedied
by bringing the lenses of the objective nearer together, in order to shorten the oblique
focus or that which forms the image of the hands. Thus in this particular or
exceptional case a shorter distance between the lenses than that most favourable for
general purposes, would be proper.
The object of my invention is to provide for suitable means of conveniently varying

page_text: the distance of the lenses of the photographic objective from each other or from the
diaphragm at will, so that the saine may be expressly and accurately adjusted for any
size of diaphragm, and also for any angle of field or size of picture, if required, or, as
in the case of the portrait objective, for any distance of object or difference of distances
of different parts of the object. I accomplish this end in several ways, which 1 describe
as follows:-
The accompanying drawing which is a longitudinal section of a compound photo-
graphic objective, illustrates my invention in a most accomplished form, showing my
new adjustment as being immediately and in such a manner combined with a so called
iris-diaphragm, as to act automatically in accordance with the diaphragm, when the
latter is operated.
A, B and C, are the constituents of the objective, A being the front lens, B the
back lens, and C the diaphragm of the same. a, a, is the case of the iris-diaphragm,
carrying at its sides the tubes, b and c, which are firmly secured to the same, and
enclosing the revolving plate and the blades, usually eight in number, of which,
however, only one k, is shown in the drawing. The blades are with one end / hinged
symmetrically around the center of the apparatus, and at their other ends they are
connected with the plate q, by means of the pin j, in such a manner as to form an
approximately sound opening which is contracted by the turning of the plate one way,
and widened by turning the other way. The turning is effected from the outside by
the corresponding turning of the ring e, with which the plate is connected by the
pin h, in the usual manner.
This concludes the necessary description of the well known iris-diaphragm and the
other known or old parts of the apparatus, while in the following I describe only those
parts which embody my invention.
The ring e, is united with the ring y, by means of the projections & and a¹, which
are connected with the corresponding projections and f', of the ring y. The rings
are each provided with a female screw w, w¹, which actuate the corresponding male
screws of the sliding tube m, and the ring g, respectively; one of the screws is right-
handed the other left-handed. The tube m is loosely fitted over the fixed tube b, and
is provided with a little block s, which slides in the longitudinal slot o. The tube i,
which is loosely fitted inside of the tube c, is connected with the ring g, by means
of the pins p, and p', which slide in the respective longitudinal slots n, n', of the
tube c.
The lenses A and B are secured to the respective sliding tubes m, i, by means of
their cells u, v.
When the ring e, is turned one way or the other, the aperture of the iris-diaphragm
will, in the well known manner, widen or contract, according to the direction of the
turn, and at the same time, the tubes m and i, will slide in opposite directions, thus
lengthening or shortening the distances of the lenses A and B, from the diaphragm C,
and owing to the corresponding arrangement of the screws w, w¹, these motions will
be in the required accordance to the changes of the diaphragm, viz.: the lenses will
move toward the diaphragm, when the latter is contracting, and separate when the
same is widening; while the threads of the screws are such as to so regulate the rate
of the motion, that with any size of aperture of the diaphragm, from the largest to
the smallest, the lenses will attain the proper positions for the best possible correction
of the field of the picture. This will also be true with the angle of field or size of
picture, since not only the diaphragm is to be the smaller, but, for the best possible
correction of the optical errors, also the distance of the lenses is to be the shorter, the
wider an angle of field or view the photographic picture to be taken with the objective,
is to represent.
Thus no attention need be paid to the adjustment, in operating this apparatus, but
the simple action of setting the diaphragm to the desired size of opening, will suffice,
and automatically place the lenses in the proper position. In fact, whatever the
outside conditions may be, it is impossible to use this objective otherwise than at its
best possible performance, provided the size of the diaphragm is properly adjusted
and adapted to the case.

page_text: Although the iris-diaphragm is probably the best adapted to act in combination
with my automatic adjustment, I do not limit myself to this particular type, but any
other mechanism, in which the size of the diaphragm is regulated in a similar or
Nor do I limit
suitable way, may he employed for the purpose in place of the same.
myself to the special device of the adjustment itself as described, since many changes
in the same are admissible and may even offer advantages to some particular
requirements. For instance only one of the lenses, say the front lens, may be made
adjustable, while the back lens be given a fixed position, same as in ordinary objectives.
This arrangement will, in fact, fully answer the purpose for some certain kinds of
compound objectives and he much simpler.
Furthermore, my invention is by no means confined to the compound objective,
that is, to such which consist of two lenses, one in front and the other back of the
diaphragm as described, or of three or more lenses, but it may just as well, and with
equal advantages, be applied to the ordinary single objective, that is, to such which
consist of only one (achromatic or non-achromatic) lens and a diaphragm, since the
altering or adjusting of their distance from each other has precisely the same benefitial
effect as in the compound lens. Besides this, numerous suitable but non-automatic
devices for effecting the required adjustment are possible and some of them even
desirable and preferable in particular cases or for certain special objectives, a few of
which I describe as follows:
1. I give the objective tube the minimum length, that is, such as corresponds with
the smallest opening of the diaphragm; and provide the objective with extra extension
tubes or so called adapters, of different lengths, to be screwed either on one end of the
tube only preferably onto the front end, or one on each end of the same, and then
screw the lens or lenses onto the adapter or adapters.
2. I provide the objective with two or more interchangeable tubes of different
lengths, having fixed diaphragms of such exact sizes or openings as correspond with
the lengths of the respective tubes.
3. I provide the objective with a sliding tube, or with two of such tubes one on
each end, which is or are to carry the lens or lenses similar to those illustrated in the
drawing, but without the adjusting screws w, w¹, so that the diaphragm and the lens
or lenses are to be adjusted separately.
4. In order to facilitate the finding of the proper position of the lens or lenses,
I provide the adjustment with index and graduation, which indicate the exact position
of the lens or lenses for any given size of diaphragm.
5. In order to facilitate the moving or adjusting of the tubes, I provide the same
with rack and pinion, or any suitable screw or lever arrangement, to be operated by
hand. This arrangement is particularly well adapted to the portrait objective,
where the lens adjustment is required to be independent from the diaphragm
apparatus.
Any of the above described devices may as well be applied to the single objective,
same as the automatic mechanism.
It must, however, not be inferred from the particular descriptions of the several
devices which I have adopted in the practical embodiment of my invention, that the
latter is necessarily limited to such details. But on the contrary, the principle of my
invention may be utilized through the medium of very different mechanism which,
however, may be readily devised by any mechanic or optician, since the principle of
my invention has been communicated to the public.
Having now particularly described and ascertained the nature of my said inven-
tion, and in what manner the same is to be performed, I declare that what I
claim is :-
1. In a compound photographic objective, the variation or adjustment of the
position of the lenses or their distance or distances from each other or from the
diaphragm, substantially as herein specified and for the purpose described.
2. In a single photographic objective, the variation or adjustment of the distance

page_text: between the lens and the diaphragm, substantially as herein described and for the
purpose specified.
3. In a photographic objective, the variation or adjustment, of the distance or
distances of the lenses from the diaphragm or from each other, for different sizes of
diaphragm-opening, substantially as specified, for the purpose described.
4. In a photographic objective, the variation or adjustment of the distance or
distances of the lenses from the diaphragm or from each other for different angles
of field or sizes of picture, substantially as specified and for the purpose described.
5. In a
photographic objective, the variation or adjustment of the distance or
distances of the lenses from the diaphragm or from each other, for different distances
of the object from the objective, substantially as herein described.
6. In a photographic objective, the variation or adjustment of the distance or
distances of the lenses from the diaphragm or from each other, for different distances
from the objective, of different objects or subjects, or parts of the same embraced in
the image or picture, substantially as herein described, for the purpose specified.
7. In a photographic objective, a mechanism or contrivance, by which the distance
of the lens or lenses from the diaphragm, or the distance or distances of the lenses
from each other, can be varied and adjusted for different sizes of diaphragm opening ;
or for different angles of field or sizes of picture, or for different distances of the
object or subject from the objective, or for different distances from the objective, of
different objects or subjects or parts of the same embraced in the image or picture,
substantially as herein described and for the purpose specified.
8. In a compound photographic objective, the combination, with an iris or other
suitable diaphragm, of a mechanism or contrivance, which automatically lengthens the
distances of the leuses from the diaphragm, or the distance or distances of the lenses
from each other, when the size of the opening of the diaphragm is increased, and
shortens said distance or distances, when the size of said opening is diminished,
substantially as described, for the purpose specified.
9. In a single photographic objective, the combination with an iris or other suitable
diaphragm, of a mechanism or contrivance, which automatically lengthens the distance
between the diaphragm and the lens when the size of the opening of the diaphragm is
increased and shortens said distance, when the size of said opening is diminished,
substantially as herein described and for the purpose specified.
Dated this 29th day of November 1890
J. P. BAYLY,
18, Fulham Place, W., Agent for the Applicant.