An Optical Projecting Instrument for Sketching..
Year: 1892

page_text: Date of Application, 9th Mar., 1892
Complete Specification Left, 9th Dec., 1892-Accented. 9th Mar., 1893
PROVISIONAL SPECIFICATION.
An Optical Projecting Instrument for Sketching..
I, ALBERT HENRY MARSII, Bookkeeper, of 5, Waldeck Road, Carrington, in
the Town and County of the Town of Nottingham, do hereby declare the nature
of this invention to be as follows:-
The principle of the instrument is the same as that of the camera, obscura, with
this exception, that the inverted image produced by the lens is, by an arrangement
of mirrors, or a prism, or one of these with a second lens, projected on to a screen
in its natural position, this effect being obtained by again inverting the first image,
formed by the front lens, in one of the following ways.
(a) By reflecting the first image, by means of a mirror or prism, through a
second lens, which inverts it and forms an image on the screen, or
(b) By causing the image to be twice reflected from mirrors.
In
The instrument constructed by the first method consists of a heavy baseboard, a
second board being attached to the front of this by a hinge, or otherwise, so that it "
stands at right angles to the baseboard, and by means of the hinge can be inclined
at any angle required and fastened in that position by a simple arrangement.
the upper portion of this front a hole is pierced in which is fastened a short tube,
and in this slides the tube containing the lens. A small box, with a circular
opening for the tube, fits on the posterior end of the lens tube and this box contains
a silvered glass or other highly reflecting plane mirror, inclined at an angle of 45°,
or a triangular glass prism, by which the image is reflected downwards. A sliding
tube is fixed to the under surface of this box, opposite a second circular opening,
and contains a second lens. The apparatus is arranged so that the image from the
first lens, reflected by the mirror or prism, is formed just beyond the principal focus
of the second lens, which thus forms a "real" image on the screen below, inverted
in relation to the first image, but in its natural position to an observer looking down
at it. The screen consists of a board on which may be fastened drawing paper or
other material and the image traced over with pen or pencil, &c., as desired. Two
sides and a top piece are also attached to the front so that they form a kind of box
the interior of which is comparatively dark, and, for convenience, these sides and
top are preferably made to fold, so that by removing the lenses and reflector the
instrument may be folded up.
In the instrument constructed by the second method of projection two plane
mirrors are arranged at right angles, fixed to the two internal faces of a triangular
box, the face opposite the angle being open this angle is arranged opposite the
front lens and the rays of light striking the top mirror at an angle are reflected to the
bottom mirror; the bottom mirror reflects them forward as a real and erect image,
where a sheet of drawing paper. or other material, is placed, and the image traced
on it. The triangular box containing the mirrors is fixed opposite the lens and so
arranged that it can be rotated about an axis passing through the angle formed by
the mirrors, and the mirrors thus fixed at the required angle.
The two latter form has also sides and top, as in the first arrangement, thus
forming a kind of box of which the interior is comparatively dark. The front lens
is directed towards the object, landscape, &c., of which a picture is desired and
focussed on the screen by moving the mirrors and lenses till a distinct image is
obtained. By fitting a cap on the front lens, in either form, the image is "shut
off." leaving only the real drawing, and by lifting up the top of the " box" this
may be examined from time.
By a lens is meant a converging lens, either simple or compound, the prisms are
of glass, and the mirrors preferably of silvered glass, the other portions of the

page_text: instrument being made of wood, carpboard, or other material, as found convenient.
And the advantages I claim are that a real image of the object required is
projected directly on to a sheet of paper or other preferred material, in its natural
colours, and in the same position as it appears to the eye, in a convenient manner
for sketching or tracing, and that by altering the focus of the lenses and position
of the screen this image may be either enlarged or reduced at will, and that the
drawing can be examined from time to time throughout its progress.
.Dated this 8th day of March 1892.
ALBERT HENRY MARSH.
COMPLETE SPECIFICATION.
An Optical Projecting Instrument for Sketching.
I, ALBERT HENRY MARSH, of 5 Waldeck Road, Carrington, in the Town and
County of the Town of Nottingham, Bookkeeper 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:-
The principle of the instrument is that an image of an object, such as a landscape,
machinery, picture &c., is formed by a lens, and this image is projected by means
of one or more plane mirrors, or a prism, or a second lens and mirror, or by various
combinations of these, on to the required surface in a convenient position for
sketching, which consists in tracing over the lines with a penci! or other material.
As the instrument is capable of assuming a variety of forms it will be convenient
to divide them into two classes, in the first of which a single lens is used and in
the second two lenses, and to take them in the following order.
For several of the methods described a box may be used closed on all sides but
one, at the back, where the sketcher's head is placed, thus forming a dark interior
in which the projected image is visible. In the upper portion of the front a hole
is pierced in which is fastened a short tube and in this slides a tube containing a
lens. On the end of this tube, inside the box, are fixed the mirrors, boxes, &c.,
which project the image on to a board in the interior, placed at the necessary angle,
on which the drawing paper, &c., may be fastened. If desired the sides, top, &c.
may be made to fold, so as to close up when not in use.
The front of the box, which supports the lenses, &c., by a recent improvement
I replace by a stand, the height of which can be varied, and which can be inclined
at any angle, and the sides of the box by a cloth which gives a dark interior in any
position and is more convenient to manipulate.
«
CLASS 1.
In Fig. 1. A and B represent two flat pieces of brass, which may be about 5th of
an inch thick and half an inch wide, though the proportions are immaterial, these
being the dimensions I use for a quarter-plate" lens, but a larger lens would
require thicker metal. The middle portion of these, CD, C¹ D', is stamped or
cut out, so. that we have practically a thin, oblong frame. A screw thread passes
through, the openings at CD' and a wing nut being screwed on at either side, as
shown at E, we can either fasten them tightly together or slip them up and down
and fasten them in any position. A third flat piece of brass F has another Hat
piece of brass G soldered or fastened at right angles to it, this latter having holes
at HJ, through which pass screws or large drawing pins to fasten it to a board
when in use. If desired G may be replaced by a clamp. A screw thread is passed
through the holes at F and K and a wing nut screwed on at either side. A tube L
of brass or other material has. a flat piece of brass soldered to its under surface
at M, or a brass ring or other means used to clasp the tube terminating in the under
piece M. A screw thread is passed through the holes at M and N and fastened with
a wing nut on either side, as before. Another tube O, containing the lens O,
slides in the tube L, or it may be moved backwards and forwards by a rack and

page_text: pinion, if preferred. A perspective view of the instrument is shown in Fig. 2,
which shows how the pieces of brass are put together and indicates the use of each
part. Wing nuts are used as being more convenient for the fingers to tighten and
untighten as the slips of brass are moved up and down, to alter the length of the
arrangement, or incline it at various angles. Ordinary nuts may be used but are
not so convenient in use. It will be seen that the lens tube may be made higher
or lower and inclined at any angle in a vertical plane. The total height to which
the brasses can be extended is about twice the focal length of the lens used. If
required to extend longer than this a third oblong piece of brass is provided, as
at P, which is inserted between the strips B and A with a screw thread and wing
nuts, as before.
A plane mirror, either metal or thin silvered glass and of either circular or
rectangular shape, has a split brass tube soldered or fastened to the back at its
centre, R Fig. 3. Through this is passed a stout wire S T and bent to the shape
shown, the ends being soldered to the ring V, which is of such size as to fit tightly
on the end of the tube L. The mirror is placed on the end of the tube by means
of its ring and inclined at an angle of about 45°.
In order to use the instrument I put the parts together as described and fasten
it to a board by means of screws or stout drawing pins passed through the holes J
and H, as shown in Fig. 2. The paper on which the image is to be projected -is
fastened to this board by drawing pins. If a canvas is used I fasten the instrument
directly on to the frame of the stretcher, or if any other material, as a plaque,
opal, &c. I arrange for the image to be projected directly on to this. I then
direct the lens tube to the object. An image is formed by the lens, and projected
by the mirror on to the board at I'. This image being lighted up by the light
around it would be invisible, so I take a cloth of some opaque material, such as
velvet, serge, &c. (Fig. 7) either square or any other desired shape and cut out a
hole in the centre rather larger than the aperture of the tube L (Fig. 2). Round'
this hole I saw or fasten an elastic band (shown by the dotted line Fig. 7) smaller.
than the tube L, or-so arrange by means of elastic that I can constrict the aperture"
in the cloth. The cloth is then brought to the front of the instrument, the
tube pushed through the hole, when the elastic causes the cloth to close round
the tube, and the upper portion of the cloth brought over the top of the instrument
till it falls over the back. I represent this by the dotted lines in Fig. 2 and it
will be seen that I obtain a kind of loose tent, covering the drawing board and
instrument but leaving the aperture of the tube free to be directed towards the
object. I arrange for the cloth to be sufficiently large to give plenty of room
and be convenient in use. I find a cloth one yard square ample for a quarter
plate lens and it will be seen that I can easily insert my head and the hand con-
taining the pencil for sketching underneath the cloth when the cloth falls loosely
over my shoulders and round the board and I can clearly see the image depicted on
It will be observed'
the paper and trace over it with the greatest convenience.
that I can put my head and hand under the cloth in any position, either at the'
side X, W, Y or. Z, and in many cases it will be found that the cloth may be
looped up so that the instrument is enclosed on 3 sides and the head forms a shade
on the fourth side without being necessary to cover it with the cloth. It will also
be understood that in any of the positions to be described the cloth can be
arranged to cover the board and instrument leaving the lens uncovered, giving a
dark interior in which the head and hand can be inserted so that the image can be.
easily seen and traced. This being understood I will describe the formation of the.
image.
The lens is directed towards the object (Fig. 2) which may be a landscape,
figure, picture or anything required, and, of course, well lighted. For convenience
of illustration a candle is shown. The lens forms an inverted image of this on the
posterior side X and the mirror reflects this down on to the board at I. It will
now be seen that if I view this image from the side X the image is inverted, if I'
look at it from the sides Zor W it appears sideways, but if move round to the

page_text: side and look at the image with any back to the object it appears erect, that is,
in its natural position, and from this side I draw the image when this arrangement
of the instrument and board is convenient. If the object is one that can be inverted,
such as a picture, photograph, statuette, &c., its image as viewed from X will be
erect," and in the case of such objects, I invert them and trace the image from the
side X. To obtain a sharply defined image the brass frame or support may be
raised or lowered or inclined at any angle in a vertical plane to bring the image
into the desired position on the board, or the lens tube moved in or out, as
required.
22
If now, without altering the arrangement, I incline the board (either to the right
or left) till it is vertical, the lens and edge Y of the board pointing to the object,
the brass frame becomes horizontal, but the image being still formed vertically
(and inverted) in space by the lens is cast on the board vertically. If the object is
erect the image is inverted, but if the object can be inverted we obtain an erect
image. This is a very convenient position for objects that can be inverted as I
can support the board vertically on an easel, or other arrangement, and sit sideways
to the object but looking directly at its image on the board. Other positions for
using the instrument may be found and may be useful in special cases, but I have
indicated the most convenient ones.
Another method by which I procure an “erect” image of an "erect" object is
by using two plane mirrors constructed like Fig. 3, one at the anterior, the other at
the posterior end of the lens tube. This is sufficiently indicated by the diagram in
Fig. 4 where L is the lens tube and lens, R the anterior mirror, R¹ the posterior
mirror, I the object, and its image on the board, the dotted lines shewing the
course of the rays. The dotted line WZ shows how the cloth is arranged. It
will be seen by studying the formation of the image according to the laws of optics,
that the image though "erect" is "laterally inverted," but it is a method which is
often useful where lateral inversion is unimportant or desirable.
Fig. 5 shows a convenient form of double mirror which I use to obtain an erect
image though laterally inverted. R is a mirror constructed like Fig. 3, (in this
case rectangular as being more convenient) but it has a second mirror R' joined to
it by means of the hinge E', or any other method. This hinge works stiffly so that
the two mirrors can be inclined at any angle to each other and remain fixed in that.
position, or by turning R¹ right over on to the back of R it can be used as a single
mirror. Fig. 6 shows the method of using it L is the lens and tube, R R the
double mirror, I the object, and its image on the board, the dotted line W'Z'
representing the cloth.
I
I construct another modification of the instrument in the following manner.
construct a rectangular box as shewn in Fig. 8. The proportions may be
considerably varied but for a quarter plate lens I use one 31" × 1 × 2″. In the
interior are two plane mirrors each inclined to the front at an angle of 45°, and,
consequently having an angle between them of 90°. Opposite each mirror a
circular hole is pierced, in which is fixed a short length of brass tube. The lower
one L' is made to fit tightly on the end of the tube attached to the top of the
brass stand previously described. The upper tube O" is made so as to allow the
tube containing the lens (which may be removed from the tube at the top of
the brass stand for the purpose) to move stiffly in it. If desired, and the focus of
the lens will allow it, the distance between the mirrors R R may be increased,
and the box constructed in two parts one sliding within the other, but this is.not
necessary. In Fig. 9 the diagram represents the box fitted on to the tube at the top of
the brass stand by which it is supported above the board, the board being horizontal.
The upper aperture of the box contains the lens tube. The cloth is represented by
the dotted line W! Z. To the end of the tube L is fitted one of the nioveable
mirrors R inclined downwards. An image of the. candle I is formed by the lens:
inverted, reflected from the mirror R" to R" from R" through the tube L to R:
which throws it down on the board as shown, the image, viewed from the back,s
appearing inverted. The box RR" can be turned completely. round the tube L

page_text: (which, with its mirror, remains fixed in the same position) and, fitting tightly on
the end of this tube L can be fixed at any desired angle. By simply turning this
box round the tube L through an angle of 45°, the image on the board will change
from an inverted to an erect image, this fact depending on the optical law that an
image moves through twice the angle that the mirror moves, so that, according to
the angle at which the box is fixed, the image may be sketched either from the
sides W, X, Y or Z, in its natural position. If, now, I place the board vertical,
with the edge Y towards the object, the brass stand becomes horizontal, and by
turning the box R" R" round the tube L, towards the board, till this box is
vertical, an image of the object will be formed on the board, which I sketch in its
natural position by standing sideways to the object. The lens O may be removed
and used in the tube L if desired, leaving the image to be formed in the upper
mirror R through the open aperture. Many other positions may be found but
the foregoing are sufficiently illustrative.
The single plane mirror described may be replaced by a triangular glass prism.
If a prism is used holes are bored in the centre of each end, in which are cemented
brass pins. The ring & bent wire terminates in short brass tubes at Sand T¹ (Fig. 10)
which fit tightly on the brass pins at the end of the prism. In use the light enters
at one face and is totally reflected from the next passing out through the third face.
There is thus no double reflection as with a silvered glass mirror.
2ND CLASS.
It consists of a
One form of the instrument in this class is shewn in Fig. 11.
small square box of wood, cardboard, or other light material A' B', in the interior
of which is a plane mirror R, which moving on a horizontal axis (a brass rod passing
through a split tube soldered or fastened to the back of the mirror, the ends of the
rod coming out on each side of the box at about the centre) can be inclined at any
angle. In a circular opening in the centre of the front a short tube is fixed L'
Fig. 12 which fits on to the tube attached to the stand in Fig. 2. A circular
opening is made in the centre of the under surface of the box and in this is-fixed
another tube O, within which slides the tube 0' containing a second lens. The
box is supported on the stand previously described and covered with the cloth and
is so arranged, by moving the tubes in or out, that the image formed by the front
lens, reflected downwards by the mirror, is formed just beyond the principal focus
of the second lens, which thus forms a "real" image on the board below, inverted
in relation to the first image but in its natural position to an observer looking down
at it. By moving the lens O' in or out and at the same time altering the length of
the brass stand to secure a distinct image, the size of the image may be varied.
This form may also be used with the board vertical, the observer standing sideways
to the object as described for the single lens instrument. The box may be of any
size so long as it is sufficiently large to allow of the distance necessary between the
two lenses being obtained which, of course, varies with the length of focus of the
lenses employed. For a quarter plate lens of 5 ins. focus and a second lens of
about 1 in. focus I use a box 2 ins. square.
A screw
Instead of the box a wide tube may be used, shewn at Fig. 14, the two lenses
fitting one at either end. A thin piece of brass, about in. wide, is used to tightly
clasp the large tube round the centre, holes being made near the ends.
thread is passed through the holes in the strip of brass and the top of the stand N
in Fig. 1and secured by wing nuts. The plane mirror fits on the end tube O'.
This may be usel with the board either horizontal or vertical (sideways, as
previously described. The large tube may be constructed of several parts sliding
one within the other, like a telescope, so that it may be closed up when not in use if
desired.
By a lens is meant a converging lens, that is one which gives a real image, and
may be either simple or compound, the sharpness of the image depending on the
kind of lens used. Photographie lenses answer the purpose well. The mirrors
may be either of polished silver, or thin silvered glass, the latter preferred as the

page_text: surface is always bright and if the glass is sufficiently thin double reflections are
not troublesome. The other portions of the instrument may be constructed of
wood, metal, or cardboard, as found convenient, the only requisites being lightness
and rigidity. It will be understood that where measurements are given they are
only approximate, as they depend principally on the focus of the lens used, and
may by the construction of the instrument be varied to a considerable extent.
I prefer for the single lens instrument lenses of rather long focus as they are more
convenient in use and allow the head and hand more room and consequently more
freedom of movement under the cloth. The interiors of all tubes, boxes, &c. are
blackened to prevent internal reflections and diaphragms used for the lens when
required, but it will be understood that as large aperture as possible should be used
to obtain a better lighted image.
And the advantages claim are that by means of my arrangements of mirrors
and lenses described I obtain a real image of the object required, projected directly
on to a sheet of paper or other preferred material, in its natural colours and in the
same position as it appears to the eye, in a convenient manner for sketching or
tracing, and that the drawing may be examined from time to time by simply lifting
the cloth.
Having now particularly described and ascertained the nature of my said inven-
tion, and in what manner the same is to be performed, 1 declare that what I
claim is
1. A moveable stand, constructed so as to be capable of being lengthened or
shortened, inclined at any angle, and fixed firmly by screws & nuts in any position,
substantially as described.
2. A cloth with elastic aperture, that admits of a part of the apparatus, such as
a lens tube, being above or outside, the remainder being underneath in a kind of
dark chamber in which the head and hand may be inserted in any aesired position,
substantially as described.
3. A moveable mirror that may be fitted on to the end of a tube and inclined
and fixed at any angle substantially as described.
4. A double mirror, or two mirrors joined, that may be fitted on to the end of a
tube & inclined at any angle to the tube & each other, substantially as described.
5. A rectangular box with two mirrors and apertures and its use in combination
with the other parts, substantially as described.
6. A square box with two apertures containing lenses at right angles to each
other, and internally an inclined mirror, and its use in combination with the other
parts, substantially as described.
7. A wide tube with a lens at each end and its use in combination with the other
parts, substantially as described.
8. The combination of any or all of the parts described, in the manner described,
or in similar ones, so as to obtain an image of an object in comparative darkness,
projected on to the required surface, that may be seen by the observer in its natural
position and sketched or traced over.
Dated this 8th day of December 1892.
ALBERT HENRY MARSH.