Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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~ BACKG~OUND OF TEIE INVENTION
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1. FIELD OF T~IE INVENTION
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This invention relates to a teaching aid which demon-
strates the component pure spectral colours of white light and
the effect of selective recombina~ion of a particular yroup and
intensity of -those pure spectral colours to form an area of light
of uniform colour.
2. DESCRIPTION OF THE PRIOR ARI~ :
Historically, Sir Isaac Newton was one of the first per- -
sons to conduct an experiment whereby the colours of the spectrum
produced by passing white light through a first prism were re-
combined by means of a second prism or lens to produce the origi-
nal white light, thereby demonstrating conclusively that white
light was a mixture of spectral colours. Since then,the sciences
of colourimetry and spectrophotometry have becomeextremely complex ;
yet many of the principles and equipment used today are based on
the eonclusio~ originally demonstrated by Newton. This invention ;~
relates to an aid for the teaching and understanding of these
basic principles.
SUMMARY OF THE INVENTION
To this end, in one of its aspects, the invention provides
an improved teaehing aid to demonstrate the component pure spectral
eolours of white light and the effect of selective recombination of
a particular group and intensity of these pure spectral eolours to
form an area of light of uniform colour.
The invention provides a teaching aid for demonstrating
the prineiple of selective colour combination and recombination
3~ which comprises a light source emitting light, a diffraction means
adapted to diffract said emitted light, a selective spatial filter
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1 means adapted to selectively filter the diffracted light, the
spatial filter being placed at the spectrum formed by the di~fracted
light, a first focusing means placed subsequent to and near the
selective spatial filter means adapted to focus the selectively -
filtered light to a subsequent first viewing position, a beam
splitting means adapted to split the focused and filtered light
into at least one split beam and one t~ansmitted beam, the beam
splitting means placed subsequent to the first focusing means and
in front of the subsequent first viewing position, focusing means
10 adapted to focus the split beam to a subsequent second viewing -
position.
In another of its aspects, the invention provides a
teaching aid which comprises a light source illuminating a
uertical slit and a first focusing means adapted to focus the
light emitted rom the slit to a blazed diffraction grating, a
selective spatial filter placed in the spectrum of the light ~-
emitted from the grating, a second focusing means placed subseqùent ` -
to and near the selective spatial fi~ter, the second focusing `
means adapted to focus the selectively filtered light to a subse-
20 quent first viewing position, a beam splitting means adapted ;
to split the focused light into a split beam and a transmitted
beam, a relay lens adapted to relay the split beam to a mirror,
the mirror adapted to reflect the split beam to a subsequent second
viewing position, the subsequent second viewing position of `~
the split beam and the subsequent first viewing position of the
selectively filtered transmitted beam being in the same conjugate !, ,
plane.
Further objects and advantages of the invention will
appear from the following description taken together with the
accompanying drawings.
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RIEF DESCRIPTION OF _HE DRAWINGS
FIGURE 1 is a plan view of the invention of the present
invention.
FIGURE 2 iS an isometric view of the invention of the
present invention.
FIGURE 3 illustrates a simple diffraction grating.
FIGURES 4 to 7 illustrate various selective filters used in
the present invention.(These-figures appear on the page with Fig. 1.)
DESCRIPTION OF _ E PREFERRED EMBODIMENT
The present invention discloses a device which demon-
strates the principle of additive and subtractive colour. The
word "colour" in the present specification is used in the visual
sense to describe the integra-ted effect of many pure spectral -
colours rather than to the pure spectral colours themselves.
The principles of additive and subtractive colour in
relation to a three colour system may be clearly demonstrated by
the following device.
Referring to Figure 1, a light source lO emits white
light which impinges on a dispersion means 12. The white light
is then dispersed according to its wavelength and passes through
a focusing lens 14 and is imaged at position 16. A selective
spatial filter means 18 is placed before the lens 14 and this filter
selectively filters the light from the dispersion means 12 onto ;
the focusing lens 14. A beam splitter 20 is placed subsequent ,!` ~ .:
to the lens 14 and in front of the position 16. The beam `
splitter 20 splits the filtered light 22 and reflects a portion -
thereof to a relay lens 24 which in turn relays the split beam `
26 to a reflecting device 28 which in turn reflects the light
to a screen 30.
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The screen 30 thus becomas a function of the selective
filter 18 and demonstrates which parts of the spectrum are select-
ively filtered. The viewing position 16 shows the resulting
~olourof the light after the filter 18 selectively filters the
light. Thus, if the screen 30 and the position 16 are placed on ~
a projection screen, the effect of selectively filtering dis- ~ -
persed white light is shown by the integrated result of the light ;;
at the position 16. When the design of the selective filter is ~;;
varied, these variations are shown on the screen 30 as a
10 function of the filter 18 and the effect is clearly seen by the ~
integrated result at position 16. - ;
The source 10 may comprise a standard 35 mm slide pro-
jector having a light source and a projection lens. As shown ~ -
in Figure 2, the projector 32 is used to project an image of a
vertical slit 34 to a position 36. The present invention is not
restricted to one utilizing this pro]ector and it is recognized
that an~ suitable source of white light may be substituted
therefore.
The dispersing element 12 is placed immediately after
the projection lens 38. It is understood that any dispersion
means ma~ be used and the preferred embodiment of the device uti- ~
lizes a diffraction means as the dispersion element and reference -
will now be made to the device utilizing a diffraction means.
The simplest form of a diffraction grating is a set of
parallel lines or grooves as seen in Figure 3. The light is
diffracted at the lines or grooves depending upon the wavelength
the longer the wavelength, i.e., the red, the greater the angle
of diffraction will be.
When a collimated or parallel beam of white light is
3~ directed through a dif~raction grating and then a lens, a spectrum
is produced. The grating itself may be "blazed" to produce pre-
ferentially the maximum light in a particular order if desired.
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1 The spread or the dispersion angle of ~he ligh-t emerging
from the diffraction grating can be calculated according to the
following drawing and equation:
ka!:
N ~ ~J
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wherein A represents the wavelength of the light
a represents the grating spacing
m represents the order O fi +2 etc. `
Sin ~+ Sin~= m~ -
a - --
Thus, if the incident beam is normal to the grating, thena = O.
In the first order, where m =
Sin~ a
a
Thus, the angle ~changes as Sin -1 ~ or the wavelength of the `i`
light. For small angles, this is approximately in direct propor~
tion to ~ .
If a line or slit source of light is used and is collimated 1
by a ~irst lens onto the diffraction grating, the beam will be
deviated by the diffraction grating dependent upon the wavelength.
The beams are then brought to a focus by a second lens forming a
set of slit images of the spectrum of the source in each wavelength.
The resolution depends upon the width of the slit. A large ;-` ~
slit width means that each wavelength has considerable overlap ~ ;
and the colours are partially integrated or mixed.
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1 The diffraction gratings may be both of the reflection or
the transmission type and the same application is applicable.
For multiple orders, the following occurs:
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when m = 0. Sin ~ ~ Sin ~ = 0
Sin ~ = Sin ~ ~
c~ = ,~ , . ..
Thus, there is no dependence upon the wavelength and the ligh-t
remains white, and is not dispersed or deviated.
when m = 1, Sin ~ + Sin~
when m = -1, Sin~ + Sin ~
Similarly, the same equation is applicable for all orders of m
limited by Sin~ =`1.
It has been found that blazed gratings put up to 70~ of
the total light into a single order (usually m = +1).
Thus, when a collimated beam of white light is passed `
through a diffraction grating followed by a lens, a spectrum is
produced.
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The selective spatial filter 18 is placed in the spectrum
~ormed by the dispersion means 12. ~ pair of guide members 40, 42 `
may be placed in the same plane as the spectrum to hold the filter ~
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18 in place, in order the various parts of the spectrum can be
blocked.
The selective filter 18 may be of infinitely variable
shapes. Figures 4, 5, 6 and 7 show four possible shapes of filters
which may be used in the present device. Filter 44 shows a blocking
oE the green light; filter 46 shows a blocking of blue light;
filter 48 shows a blocking of red light and filter 50 shows an
arbitrary pattern of blocking. It is clearly seen that for
demonstration and teaching purposes, an infinitely large number of
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1 spatial filters may be designed to illustrate the principle of
the present invention.
The filtered light then impinges on the lens 14 which
projects the image of the aperture of the grating 12 onto the
position 16. A beam splitter 20 (preferably a 1:1 splitter with
as flat spectral response as possible) is inserted subsequent
to lens 14. The split beam is passed through the imaging lens
24 and by means of reflec~or 28, forms the image of the spectrum
and the selective filter 18 on the screen 30. The image
produced on the screen 30 (referred to as the first image) would
be a function of the seIective filter 18.
The liyht which is transmitted by the beam splitter 20 `
is focused at position 16. This image (referred to as the `-;
second image) is the integrated or recombined light of the
spectrum transmitted at the selective filter 18. Thus, the ~`
filter 18 acts as an aperture stop for the lens 14. As the
light at the aperture of the lens 38 is not dispersed, i.e., ` `
white light, ~o also is its image at position 16 not dispersed.
If no filter at position 18 is used,the image at
position 16 will be white and the spectra at filter 18 and screen ~ -
30 is complete with all colours. If filters as shown in Figures 4 ;
to 6 are used ~green light, blue light and red light being
removed respectively), then the spectra at screen 30 will appear
as "red-blue", "red-green", and "blue-green" respectively. The
colour at the position 16 will appear as magenta, yellow and
cyan. If a filter as shown in Figure 7 is used, which is shown
predominately transmitting in the red and blue portions of the ;
spectrum, the colour at the position 16 would appear purple.
Subtractive colour principles may also be demonstrated by
the present device. For example, if a cyan and yellow filter
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1 were combined, green light would be produced. By removing the
red from the cyan and the blue from the yellow, only the light
common to both filters would be transmitted, that is, green.
Thus, it can be seen that the principles of colour
addition and subtraction may be demonstrated by the device of the
present invention.
The device may be used as follows to demonstrate the
component parts of white light and the effects of their selective
combination.
Filters are used which remove single colours from
the spectrum. If the filter as seen in Figure 4 were used, then
only the red and the blue light would be transmitted and the
colour at the viewing position 16 would appear magenta. At
position 30, the image of the filter would appear with a red
band on one side and a blue band on the opposite side with
the green band removed. Thus, the student would see first at
position 30, these colours which were transmitted and the colours ~ ~ -
which were filtered out and then the effect of this filtering
would be seen by the colour exhibited at position 16.
~0 By using the filters as shown in Figures 4, 5 and 6,
the principles o~ colour addition and subtraction can be clearly
shown. After demonstrating the aforeno~ed principle, the
principles of spectral distribution can be demonstrated by using
filters such as the one illustrated in Figure 7. These
filters do not necessarily block out an entire wavelength and
transmit other wavelengths but they filter out various portions
of the selected wavelengths. Thus, the intensity of each
wavelength passing through -the filter may be controlled. Again,
the effect of varying the intensities of the transmitted
wavelengths will be shown by cha~ging the colour at the position 16.
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1 Although the disclosure describes and illustrates
a preferred embodiment of the invention, it is to be understood
that the invention is not restric-ted to this particular
embodiment. :
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