Improvements in Photographic Cameras and other Optical Instruments.
Year: 1893

page_text: Date of Application, 4th Aug., 1893
Complete Specification Left, 6th Apr., 1894-Accepted, 9th June, 1894
PROVISIONAL SPECIFICATION.
Improvements in Photographic Cameras and other Optical
Instruments.
I, JOHN WILLIAM GORDON of the London Institution, Finsbury Circu-,
London, Gentleman do hereby declare the nature of this invention to be as
follows, that is to say :-
56
My improvements have reference mainly to the arrangements made for
focussing" a photographic camera, that is to say, for ascertaining when it is
in proper adjustment for producing a sharply defined image upon a photographic
plate. They relate also to arrangements that may be made for accurately and
effectively combining the constituent parts of a composite photograph and some
parts of my new mechanism can be adapted to serve the same purposes which are
herein assigned to them or purposes analogous thereto in connexion with other
optical instruments than the photographic camera.
The
The ordinary method of focussing a camera consists in placing a ground glass or
other diaphanous screen in the position to be occupied during the photographic
operation by the sensitive plate and then bringing the lens into adjustment for
throwing an image with the required definition upon this focussing screen.
adjustment is ascertained by observation of this image. Various modifications of
this original method have been from time to time introduced in order to facilitate
the process or to adapt it to the special requirements of a particular photographic
operation or for other purposes which it is not necessary to indicate more fully.
These methods of ascertaining the focus adjustment have all, so far as I am
aware, depended for their effect upon an observation made by the operator of
the definition of the test image.
"
The method which I have devised is entirely different in principle and rests
upon an observation not of the definition but of the dimensions of the test image.
That is to say; I apply a scale or micrometer to some selected feature of the
image and from its apparent size I determine the adjustment of the camera
necessary to secure the desired definition. It will be understood that the test
image in this case is not necessarily the image formed by the camera lens. On
the contrary it is for many purposes more convenient to use a special lens to
produce the test image and to mount this lens as an adjunct to the camera which
adjunct shall hereinafter call a "focus-findei." The "focus-finder
may be
permanently or only occasionally attached to the camera and in the form which
I prefer it will consist of three main elements (1) the lens (2) the scale or
micrometer, (3) the eyepiece. The lens should preferably be a lens of short focus
such as is commonly used for a view finder in a camera. The micrometer may
be made adjustable by the operator or it may be made to vary its reading with
the adjustment of the camera automatically. I have found that a convenient
adjustment of the micrometer may be obtained by causing it to register the
apparent size in the test image of the distance between the pupils of the eyes
of a sitter occupying a position in the focus of the camera. When this is done
automatically any suitable mechanism may be employed to connect the micrometer
with the camera so that the reading of the former may correspond to the
expansion of the latter. When the micrometer is to be adjusted by hand I find
that a very convenient action may be devised by using a screw with two threads
at different parts of its length the one thread having a pitch such that its travel
is twice that of the other in a given number of turns and then causing the slow
thread to propel the screw in one direction while the quick thread repels a nut
.

page_text: in the opposite direction. The separating or approximating motion so obtained
may be caused to actuate the microineter wires.
The eyepiece may be conveniently formed of another lens, or combination of
lenses, of suitable focus and in order to project the image into the observer's eye at
an angle convenient for easy observation it may be fitted with a mirror so arranged
as to throw the beam up at some angle intermediate between the horizontal and
the vertical directions. Another advantage resulting from the use of this mirror
is that it may be employed to render the test image erect and, if a suitable
angular mirror be used, that it may be employed not only to restore the erect
position but also to correct the reversal of sides which the image produced by the
lens has undergone. It will be obvious that my improvements in the mechanism
of the micrometer and in the construction of the eyepiece are adaptable to these
parts when used in other optical instruments than my focus-finder.
It is necessary in the production of composite photographs to have the field of
the camera mapped out so that an image can be projected upon a specially selected
spot. To facilitate this operation I may introduce a suitable screen into my
focus-finder which thus becomes a view-finder capable of great precision.
Dated this 2nd day of August 1893
J. W. GORDON.
COMPLETE SPECIFICATION.
Improvements in Photographic Cameras and other Optical
Instruments.
I, JOHN WILLIAM GORDON, of The London Institution, Finsbury Circus, in
the City of London, 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 improvements in photographic cameras and in other
optical instruments.
The said improvements have reference mainly to means for "focussing" a
photographic camera, that is to say, for ascertaining when it is in proper
adjustment for producing a sharply-defined image. upon a photographic plate.
They relate also to means for accurately and effectively combining the constituent
parts of a composite photograph. Some parts of my new apparatus can be adapted
to serve in other optical instruments than a photographic camera the same purposes
as are herein assigned to them in connection with a camera, or purposes analogous
thereto.
The ordinary method of focussing a camera consists in placing a ground glass or
other translucent screen in the position to be occupied during the photographic
operation by the sensitive plate, and then bringing the lens into adjustment for
throwing an image with the required definition upon this focussing screen. The
adjustment is ascertained by observation of this image. Various modifications of
this original method have been from time to time introduced in order to facilitate
the process or to adapt it to the special requirements of particular photographic
operations or for other purposes which it is not necessary here to indicate more
fully. These methods of ascertaining the focus adjustment have all, so far as I am
aware, depended for their effect upon an observation made by the operator of the
definition of a test image.
The method which I have devised is entirely different in principle and rests upon
an observation not of the definition but of the dimensions of the test image. That
is to say I apply a scale or micrometer to some selected feature of the image and
from its apparent size I determine the adjustment of the camera necessary to secure
the desired definition. It will be understood that the test image in this case is not
necessarily the image formed by the camera lens. On the contrary it is for many

page_text: purposes more convenient to use a special lens to produce the test image, and to
mount this lens as an adjunct to the camera which adjunct I shall hereinafter call
a "focus-finder." The focus-finder may be permanently or only occasionally
attached to the camera, and in the form which I prefer, it will consist of three
main elements (1) the lens, (2) the scale or micrometer, (3) the eye-piece. The
lens should preferably be a lens of short focus such as is commonly used for a
"view-finder" in a camera. The micrometer may be made adjustable by the
operator or it may be made to vary its reading with the adjustment of the camera,
automatically. I have found that a convenient adjustment of the micrometer_may
be obtained by causing it to register the apparent size in the test image, of the
distance between the pupils of the eyes of a sitter occupying a position in the focus
of the camera.
When this is done automatically any suitable mechanism may be
employed to connect the micrometer with the camera so that the reading of the
When the
former may correspond to the expansion or adjustment of the latter.
micrometer is to be adjusted by hand I find that a very convenient action may be
devised by using a screw with two threads at different parts of its length the one
thread having a pitch which is twice as great as the pitch of the other, causing the
"slow" thread to propel the screw in one direction while the "quick" thread repels
a nut in the opposite direction. The separating or approximating motion so
obtained may be caused to actuate the micrometer wires.
The eyepiece may be conveniently formed of another lens or combination of
lenses of suitable focus and in order to project the image into the observer's eye
at an angle convenient for easy observation it may be fitted with a mirror so
arranged as to throw the beam up at some angle intermediate between the horizontal
and the vertical direction. Another advantage resulting from the use of this
mirror is that it may be employed to erect or re-invert the test image and, if a
suitable angular mirror or series of mirrors be used, that it may be employed not
only to restore the erect position but also to correct the reversal of sides which
It will be obvious that my
the image produced by the lens has undergone.
improvements in the mechanism of the micrometer and the construction of the
eyepiece and its appurtenances are adaptable to those parts when used in other
optical instruments than my focus-finder.
It is necessary in the production of composite photographs to have the field of
the camera mapped out so that an image can be projected upon a specially-selected
spot.
To facilitate this operation I may introduce a suitable screen into my
focus-finder which thus becomes a view-finder capable of being employed with
great precision.
In order that my said invention may be clearly understood I will now proceed to
describe the same with reference by way of example to the accompanying drawings,
wherein
Figure 1 is a vertical section through the optical axis of an instrument
(hereinafter termed a "focus-finder") constructed according to my invention,
:
Figure 2 is an elevation of part of the instrument illustrating a mode of adjusting
the position of the object lens to various distances of the object,
Figure 3 is a transverse section on the line cx of Figure 1,
Figures 4, 5, and 6 show respectively, a graduated glass slide, a gauge, and an
automatic glass slide, all of which are hereinafter particularly described,
•
Figure 7 is a sketch shewing the appearance of the image in the focus finder
when a sitter is too far from the camera for correct focus,
Figure 8 is a similar sketch showing the appearance of the image when the sitter
is too near, and
Figure 9 the like when the distance of the sitter and the adjustment of the
camera are correctly coördinated.
Figure 10 is an elevation of a transparent screen upon which a suitable series of
crossed lines or other graduations.is inscribed, to map out the field of the focus-
finder as aforesaid when the apparatus is used as a view-finder.
The same letters are used.to indicate the same parts in all the figures.

page_text: A is an object lens of two inches focal length. This lens is not necessarily
achromatic, for although it would be an advantage to use an achromatic lens, the
property of achromatism is not indispensable to the satisfactory working of the
instrument in ordinary conditions. The lens is mounted in a cell B which screws
upon the tube C. This screwed joint facilitates the making of an adjustment to
be hereinafter explained. The tube C is connected at the end distant from the
object lens with a transverse plate D. The connection is a permanent one made in
any convenient way as by soldering the tube to the plate. The plate D forms a
projecting flange as shown, about the tube C for the purpose of receiving the
bolts E and affording a surface upon which their nuts F can be screwed home and
for the further purpose of affording a surface against which the glass slide G can
bear. The plate D is pierced through its centre with a circular opening H made
of a size to include the internal optical field of the instrument. The length of the
tube C is so determined that when the cell B is screwed home the focal plane to
which the image of an object distant 8 feet in front of the lens is brought, coincides
with the surface farther from the lens of the glass slide G. It will of course be plain
from this description that a permanent adjustment is made once for all by which a
correct focus is obtained for an object at a distance of 8 feet and that consequently
the focussing of objects nearer or more distant will be slightly incorrect, that is to
say will fall in planes not coincident with the surface of the glass slide G. This
however, is not a matter of any considerable importance indeed I consider it to
be a matter of merely theoretical interest and not of sufficient practical importance
to be rated a defect in the design of the instrument because with a lens of so short
a focus as that described the displacement of the focal planes from their theoretically
correct position would in practice be so slight as to occasion no inconvenience to the
user of the instrument. It may however become desirable in some circumstances
to employ in the construction of an instrument made in accordance with my
invention an object lens of greater focal length and in that case, or otherwise, it
may be desired to have the means of making an adjustment for the purpose of
obtaining a constant position of the focal plane with varying distances of the
object. I will hereinafter shew, in connection with Figure 2, how I propose to
obtain this adjustment. At present I return to the description of Figure 1.
The glass slide G is held in position by the pressure of the spring J which holds
it as shewn in the drawing. This spring J is shewn in elevation in Figure 3 and
is pierced with an opening H¹ which defines the internal optical field of the
instrument.
I have now described one half of the instrument, that, namely, which contains
'the object lens. I will now proceed similarly to describe the other half of the
instrument constituting what I may call the eye-piece.
+
The
K is the eye-glass, a lens of two inches focal length; it is mounted in the tube L
and covered by a cap N such as is commonly used in optical instruments.
tube L is bent at the point at an angle as shown. This bending secures two
objects for it causes the eye-glass to be presented to the eye of the operator, when
the line of collimation of the object leus is horizontal, in a position very convenient
for being seen through, and also it enables the mirror M to be interposed between
the object lens and the eye-glass. This mirror M is a plane mirror reflecting from
its upper surface, and its interposition as described has the effect of reinverting the
inverted image formed by the object lens A and so of presenting an image in an
erect position to the eye of the observer. In the position shewn, however, it will
not correct the interchange of right-hand and left-hand features which occurs as a
part of the inversion of the image produced by the object lens. It will be
understood by persons versed in optics that I might secure the double reinversion
and produce a fully-corrected image through the eye-glass by substituting a
rectangular mirror for the plane mirror shewn but practical considerations induce
me to sacrifice this theoretical improvement and to rest content with the vertical
correction only. This correction is for practical purposes very much more
important than the horizontal correction as will be readily understood without

page_text: A
explanation. In fact the horizontal correction is a matter of no practical
importance whereas the loss of illumination entailed by double reflection from the
two surfaces of a rectangular mirror is a matter of consequence. The practical
considerations to which I have just alluded in general terms have regard to the
production of a very cheap and simply constructed form of mirror. I use for this
purpose an ordinary piece of polished glass having a flat surface and have found
that a piece of ordinary photographic plate will serve the purpose perfectly. It is
scarcely necessary to add that the surface intended to be used as a reflecting
surface must be approximately true and quite free from such irregularities as
would noticeably distort the image. I cannot well define the degree of accuracy
required because the truer the surface and the more highly polished the better it is
for its purpose. But I wish it to be understood from the illustration here given
that a practically useful result may be obtained by the employment of very
ordinary glass and that what is known as an "optically wrought" surface is not
indispensable. The plate of glass to be used as the mirror must, of course, be
shaped so as to fit into the place which it has to occupy within the tube L.
plane coinciding with the reflecting surface of the mirror M would be cut by the
sides of the tube L along two semi-ellipses having their vertices turned away from
one another and it the elbow / were placed so that each arm of the tube made an
equal angle with the plane of the mirror then those semi-ellipses would in all
respects be similar to one another. This may be taken to be the shape of a
theoretical mirror. In practice it is not necessary to attempt even
approximation to the shape and position of the mirror as so defined. It may lie
lightly above or slightly below the theoretical position provided it be disposed in a
plane substantially parallel to the plane of the theoretical mirror. It may have
any figure which will permit it to lie within the tube in the plane selected provided
only that it presents a sufficiently extended surface to permit every part of the
field as defined by the opening H¹ to be viewed by the operator. The principles
by which the outline of this surface is determined are perfectly well known and I
nced not therefore encumber my present description with a definition of it.
practice it is sufficient to take a plate of glass of the form of a parallelogram
having a breadth equal to the diameter of the opening and a length slightly
greater than the diameter multiplied by the cosecant of the angle which
the reflecting surface makes with the axis of the object lens (the slight excess
of length being designed to prevent loss of field if the mirror should be
placed a little apart from its true position between the focus of the instrument
and the eye-glass) and then to grind away the corners of the glass plate until it fits
snugly into its place within the tube. To avoid duplicating the image by reflection
from the lower as well as from the upper surface of the glass plate recourse may
be had to many well known expedients of which the simplest perhaps is to roughen
and blacken the lower surface PP are clamps which serve to hold the mirror in
place..
a near
In
With regard to the preparation of the reflecting surface I desire to point out
that according to my construction the beam of light falls upon it under a very
small angle and is therefore reflected with very little loss of brilliancy; indeed the
angle that I prefer to use being much under the angle of total reflection for any
kind of glass it is quite unnecessary to coat the glass with any opaque substance
such as a film of silver and the completeness of the reflection depends only upon
the fineness of the polish given to the surface. Now glass being a substance which
takes a very high polish is peculiarly suitable for a mirror such as I have just
described and accordingly I use it as described, without other preparation than
such polishing as is ordinarily given to transparent glass. It is obvious that many
substances besides' glass might be used as material for such a mirror.
The tube L is fitted at its end distant from the eye-glass with a plate Q, similar
in shape to the plate D_and_perforated with an opening H" similar to the
opening H in the plate D. The two halves of the instrument are connected
together by means of bolts and nuts E, F, suitable blocks or distance pieces R

page_text: being introduced to keep the two plates apart and produce a slot through which
the glass slide G can be passed and in which the elastic spring J operates. The
spring J is held in place, as shewn, by the bending over of its upper and lower
edges so as to hold on to the plate Q. The distance of the eye-glass K from the
focus at H of the object glass is approximately two inches measured along the
bent axis of the instrument.
I will now describe with reference to Figure 2 the modification by which I
propose to make the object lens A adjustable in distance froin the focal plane at H¹
according to the varying distances of the external object viewed. The cell B' of
Figure 2 serves, like B in Figure 1, to mount the object lens and it is also connected by
a screw thread with the tube C. It is however much deeper, as shewn, than the cell B
and it is moreover provided with a milled ring to facilitate turning it upon its
tube. It is by so turning it that the position of the object lens is altered for
adjustment. In order that the position of the lens may be accurately known two
scales are used. The one, S, is drawn upon the tube C and being read by means
of the fiduciary marks drawn upon the cell 13' serves to shew the angle, not being
greater than one revolution, through which the cell has been turned. The other
scale T is drawn upon the cell B' and being read by means of a fiduciary line t
drawn around the tube C serves to determine how many complete revolutions the
cell B' has made. The proper adjustment of the object lens as represented on
these scales for any given distance of the object having once been determined may
of course be recorded for future information and the instrument may then always
be set to the required adjustment thereby.
The glass slide G is separately shewn in Figure 4. It is made of a shape and
size to slide conveniently within the slot of the instrument as shewn in Figure 1.
It has engraved or drawn upon its surface two converging lines, as shewn, upon
which certain points are indicated by horizontal lines and defined by reference to a
scale upon the camera with which the instrument now under description is intended
to be used. The positions of these horizontal lines are to be determined by
observation in the way hereinafter appearing.
In connexion with this instrument I use a gauge which may very conveniently
be in the form of a pair of spectacles as shewn in Figure 5. The eyes of these
spectacles are pierced with two small square or lozenge shaped holes each
having one diameter vertical as shewn. The vertical corners of these holes are to
be taken as the fiduciary points of the gauge. Any desired spacing may be given
to these fiduciary points and the scale upon the glass slide determined accordingly.
In my judgment the best distance at which to place them apart is 2 inches, this
being, as nearly as I know it, the average distance between the pupils of the eyes
(measured from centre to centie) of an adult person.
will now describe the use of this instrument in focussing a camera.
First, the instrument is placed so that its object lens may occupy a position as close
as possible to that of the lens of the camera. Then the gauge is placed in the plane
of the object upon which the camera is to be focussed and is viewed through the
focus-finder. The glass slide is then adjusted in the slot of the instrument so that
the converging lines upon the glass slide appear to intersect the vertical points of
the holes in the gauge. The distance between these lines at the point of inter-
section, as indicated by the scale upon the slide, is then read off. The distance
between the lens of the camera and the photographic plate must correspond with
this reading and a scale provided upon the extension apparatus of the camera
enables the operator to adjust this distance accordingly.
It will now be readily seen that for the purpose of graduating the glass slide the
operation just described must be reversed, that is to say, the camera is to be
focussed upon the gauge in the ordinary way by means of a focussing screen
introduced into the camera. Then the glass slide is to be adjusted as before
described and the points of intersection with the vertical corners of the fiduciary
holes in the gauge are to be indicated by a horizontal line drawn or engraved upon
the glass slide. At the same time a corresponding scale mark is to be made upon

page_text: the extension apparatus of the camera.
two corresponding scales may be produced.
By a series of such determinations the
The graduated glass slide just described is the simplest instrument that I have
been able to devise for the purpose which it serves. But other contrivances are
available and I will proceed to describe one with reference to Figure 6. In this
case the spring J is dispensed with and its place is occupied by a glass plate (i
which is, by cementing or otherwise, made fast to the plate Q. Across the middle
of this glass plate G₁ there is drawn or engraved a single horizontal line. The
glass slide G has delineated upon it two nearly vertical converging lines which in<
this case however must not be straight but slightly curved lines convex to one
another. A mode of delineating these lines will be indicated presently. The
slide G is in this arrangement provided at its foot with a hook or other attachment
for a fine cord which passes over a pulley V and is attached to some part of the-
camera which is displaced by the extension movements which bring about the
focussing adjustment of the camera. Thus the slide G is made to follow these.
movements and the distance on the horizontal line drawn upon the glass plate G¹
which is intercepted between the points of its intersection with the curved lines
drawn upon the glass slide G will, if the said curved lines are correctly drawn, be
equal to that which the graduated glass slide shewn in Figure 4 registers for the
given adjustment of the camera. It thus becomes obvious in what way an automatic
slide may be designed by the help of a graduated slide and it follows, since the
graduated slide is only a record of observations made by comparison of the camera
with the focus-finder, that the same series of operations from which complete
materials for the graduation of a graduated slide may be obtained will also furnish
materials for the delineation of an automatic slide.
The automatic slide just described may serve as a type of the modifications of
which this part of my instrument is susceptible and it will be obvious that very
many other modifications may be suggested. Indeed every mode of mounting and
operating wires in a micrometer is probably capable of adaptation to this part of
my invention.
I shall therefore not pursue this description farther but in what
follows shall assume that in many ways a graduated or an automatic adjustment
between the camera and its focus-finder may be established.
It will no doubt have been discerned that in recommending the use of a gauge of
the particular dimensions above specified, I have had it in view to dispense
altogether with its use in portrait photography and to supersede it by making
observations made directly upon the pupils of the sitter's eyes. Such is my object.
The substitution of the sitter's eyes for the artificial gauge presents no difficulty
and does not perhaps need explanation but to prevent any difficulty or misunder-
standing I have added three figures, Figures 7, 8, and 9, in which the appearance of
a sitter looking full at the instrument is shewn. In Figure 7 the sitter is too far
off and the glass slide and the camera need to be adjusted for greater distance. In
Figure 8 he is too near and the adjustment must be made in the opposite direction..
In Figure 9 the glass slide is in correct adjustment and when the camera is.
adjusted correspondingly the exposure may be made.
The screen shown in Figure 10 is of great use in such an operation, for instance,.
as combining the constituent parts of a composite photograph.
It will of course be understood that I have for the sake of clearness introduced
into the foregoing description many features which are not of the essence of my
invention.
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 [
claim is:
1. An instrument such as is herein before described and called a focus-finder, to.
be used in connexion with a photographic camera for adjusting the same to focus,
which comprises the following constituent parts:-Means for the production at a
convenient place for observation and under suitable conditions, of a visible image-

page_text: of some object of predetermined magnitude situated within the objective field of
the camera, means for determining the apparent magnitude of the visible image so
produced, and means for applying the determination so arrived at in such wise as
to regulate the focussing of the camera.
2. In an instrument of the kind hereinbefore called a focus-finder, the com-
bination of an object lens such as A, a micrometer such as G or its equivalent
adjusted to the reading of a predetermined magnitude in the object field of a given
camera, and a suntable eye-piece through which to view the micrometer and the
image formed by the lens A.
3. The instrument herein before called a focus-finder constructed substantially
as described with reference to Figure 1 of the accompanying drawings.
4. The modification of my invention wherein I employ such devices as are
illustrated in Figure 2 of the accompanying drawings for the purpose specified.
5. The modification of my invention wherein I replace the graduated scale G
by an automatic micrometer for the purpose specified.
6. The combination of parts shewn in Figure 1 and described in connexion
therewith, which, taken together, make up the erecting eye-piece; which com-
bination comprises the eye glass K, the tube L and the mirror M all constructed
and arranged as hereinbefore set forth.
7. The combination with the focus-finder, of a screen adapted to be used for
mapping-out the field, substantially as described.
Dated this 6th day of April 1894.
"
HASELTINE, LAKE & Co.,
45, Southampton Buildings, London, W.C., Agents for the Applicant.