Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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METHOD FOR CORRECTING NON-UNIFORM ILLUMINATION
IN OBL-[QUE PROJECTION OF SLIDE TRANSPARENCIES
CROSS REFERENCES TO RELATED APPLICATIONS:
Related to the co-pending METHOD OF MODIFYING SLIDE
TRANSPARENCIES SO AS TO PROVIDE UNIFORM ILLUMINATION IN ANGULAR
PROJECTION (Canadian Serial No. 369,699), filed January 30, 1981.
The present application is directed to a method for
selectively illuminating the modified slide transparency so
as to obtain uniform illumination of the image which is obliquely
projected upon a viewing screen.
BACKGROUND OF THE INVENTION
Field of the Invention:
Photography, particularly the projection of images
through a slide transparency and onto a viewing screen, which is
obliquely moun-ted with respect to the optical path of projection.
Image distortions in oblique projection conven-tionally include
the "Keystone effect" and non-uniform illumination. The "Key-
stone effect" results in a trapezoid shaped projected image.
Non-uniform illumination results in a degrading of the pro-
jected image quality, especially a lack of contrast and poor
color rendition, since the por-tion of the obliquely supported
viewing screen farthest from the projector receives less
illumination and the portion nearest receives greater illumi-
na-tion. These distortions will therefore create a projected
~5 image which is visually unattractive.
SUMMARY OF THE INVENTION:
In one broad aspect, the invention comprehends a method
for correcting non-uniform illumination oblique projection of
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slide transparencies which comprises supporting a slide trans-
parency within a projection system, and selectively illumina-ting
-the transparency such that a greater portion of light is pro-
jected through the lower portion of the transparency and a lesser
portion of light is projected -throug~ the upper portion of the
transparency. The light projec-ted as an image is magnified
through the transparency, and the image is displayed upon an
angularly supported viewing screen, such -that the farthest
portion of the viewing screen receives the greater portion of
light and the nearest portion receives the lesser light.
In a further embodiment, the invention contemplates a
method for correcting non-uniform illumination in oblique
projection of slide transparencies which comprises supporting
a slide transparency within a projection system, selectively
illuminating the -transparency with an intensified light source
by tilted condensing and collimating of light towards the
transparency, such that the optical path is narrowed and its
axis diverted towards the lower portion of the transparency,
such that a greater portion of light is projected through
the lower portion of -the transparency and a lesser portion
of light is projected through the upper portion of the trans-
parency. The light projec-ted is magnified as an image through
the transparency, and the image is displayed upon an angularly
supported viewing screen, such that the farthest portion of
the viewing screen receives -the greater portion of light and
the nearest portion receives the lesser light.
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As a result, the illumination of the image
displayed upon -the obliquely supported screen .is nearly
uniform.
The selective illumination of the transparency is
accomplished by tilted condensing of collimated light, such
that the optical pa-th of light is narrowed and its axis diverted
towards the lower portion of the transparency.
The present method is especially a~apted to the use of
rear view projection consoles wherein limited space is a
critical factor. For example, a single central light source
may be employed to project simultaneously, radially ~hrough a
plurality of transparencies mounted upon an encircling carousel
and the projected images in turn reflected upwardly on to a
rear view screen. Conventionallyl the space allocated behind
such rear view screens depends upon the focal length of the
lens and the desired magni~ication ratio. Generally, a better
image is produced when the lens used has a focal lengt~ at
least equal to the diagonal of the projected image. This
focal length requirement and the requirement for right angle
projection onto the viewing screen often demands more space
than is available~ When space limitations arise, mirrors are
used to fold the optical projection path often requiring
excess depth, as illustrated in the drawings. If folded
properly, the projector can be placed in a more compact arrange-
ment.
The present method is characterized by its extraordinarysaving in space, such that a plurality of images may be trans-
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mitted simultaneously upon mul-tiple viewing screens.
DESCRIPTION OF THE DRAWINGS:
FIG. 1 is a schematic view, showing the employment of
tilted condensers to selectively .illuminate the lower portion
of a slide -transparency prior to its projection upon an obliquely
supported viewing screen.
FIG. 2 is a transverse section, taken along section
lines 2-2 of FIG. 1 and illustrating the trapezoidal negatiYe
which is selectively illuminated.
FIG. 3 is a front elevation of the viewing screen anA
showing the selective illumination o-E the image being projected
upon the viewing screen.
FIG. 4 is a schematic view of a system wherein a
plurality of slide transparencies are suppor-ted in peripheral
array with respect to a single central light source.
FIG. 5 is a side elevation, showing a proposed assembly
for selective illumination of a slide transparency for oblique
projection.
FIG. 6 is a side elevation of the tilted condensor
2~ mounting.
FIG. 7 is a schematic view of the conventional single
projection system wherein the projected image is twice "folded"
prior to display upon a rear view projection screen.
FIG. 8 is a schematic view of a dual conventional pro- -
jection system, employing dual projectors and dual mirror systems
for display upon a separate rear view screen.
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DESCRIPTION OF T~E DRAWINGS:
In FIG. 1 a central light source 20, such as a Xenon
lamp is illustrated as positioned next -to aspheric lens 22
which collimates the light towards a pair of tilted condensers
24. The condensers 24 are tilted so as to divert the optical
path toward the lo~er portion o~ slide transparency 31 posi-
tioned in slide mount 28. The transparency image is then
magnified by projection lens 26 and displayed upon viewing
screen 30.
As illustrated in FIG. 2, the diverting of the optical
path of light by the tilted condensers 24 directs more light
towards the lower portion (Area B) of slide transparency 31
and less light towards the upper portion (Area A) of slide
transparency 31. As a result, the image projected upon
viewing screen 30, as illustrated in FIG. 3, receives more
light in the upper portion (Area B) which is farthest from
the light source (distance 11) and less light in the lower
portion (Area A) which is nearest the light source (distance
12). This selective illumination of the transparency 31
achieves a uniform illuminati.on of the obliquely displayed
image upon viewi.n~ screen 30.
In FIG. 4 the method is shown as adapted to a multi-
image display reax view projection system, wherein a plurality
of slide transpaxencies are supported in peripheral array
with respect to an a~ial light source. The transparencies
are selectively illuminated and simultaneously projected
towards reflectin~ mirrors 32, 32', positioned within console
36 and, thence, displayed obliquely upon rear view screens
34, 34'.
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In FIG. 5 there is illustrated a proposed assembly for
selective illumination of slide transparencies, including
I Xenon light source 20, aspheric lens 22, tilted condensers
¦ 24, slide transparency 31, mounted in bracket 28, projector
I lens 26 and a reflecting mirror 32 mounted upon back plate 38
supported in bracket 40 by means of an adjustment screw 42 or
the like.
Aspheric collimating lens 22 may be supported in bracket
44, together with heat absorbing glass plate 46, serving to
eliminate heat damage to the slide transparency 31. Bracket
44 may be mounted upon post 48 secured slidably upon transverse
rods 50 and 52. The entire rod assembly may be supported
¦ upon posts 56 and 58 which extend to base 54. A pair of
I tilted condensers 24 may be mounted within bracket 62 which
1l is supported upon adjustable base 60, such that the angle o~
¦l tilt may be varied readily.
The slide transparency bracket 28 may be mounted and
turned upon carousel vertical post 76, extending from base
plate 74. Base plate 74 is rotatably secured between roller
assemblies 70, 72 mounted upon posts 66 and 68 extending to
carousel sub-base 64. A suitable drive means (not illustrated)
¦ may be employed for rotating the carousel base.
¦ Stationary projector lens 26, in turn, may be supported
upon post 80 which is slidably, adjustably mounted upon
horizontal rods 50 and 52.
In FIGS. 7 and 8 there are illustrated the conventional
"folding" techniques employed in rear view projection systems
and requiring extensive cabinet structure for housing of the
mirrors and projectors.
30 i In FIG. 7 a single projection source is used together
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~ith primary and secondary mirrors for display of the slide
transparency upon a rear view projection screen.
In FIG. 8 a pair of projectors are used, each with primary
l and secondary reflecting mirrors for l'folding" the projected
¦ image upon a rear view screen. ~s will be apparent, the
space requirements for l'folding" of the image and projecting
of the image at right angles, so as to avoid distortion, are
prohibitive.
According to the present method a dramatic space reduction
o ! is achieved in rear view oblique projection. The space inter-
mediate the screens may be shared by multiple projection
paths, since there is no intervening structure. According to
,, conventional oblique projection techniques, the image displayed
!l upon the rear view projection screen is both distorted with
¦! the "Keystone effect" and non-uniformally illuminated~ With
li respect to the non-uniform illumination, the lower portion of
Il the image closest to the lens is brighter than the upper
¦, portion which i5 farthest from the lens. According to the
I, present method of selective illumination of the transparency,
~ the oblique projection upon the viewing screen at an angle
of less ~r more than 90 does not result in non-uniform illumi- !
¦ nation. As a result, there is enhanced resolution and color
perception.
As will be apparent, the projection system may be superposed
so as to be mounted above the rear view screens. Also, of
¦ course, the projection angles onto the viewing screens may be
I varied selectively between each projection system and the
¦ selective illumination of the slide transparencies may be
! modified by changing the degree of tilting of the condensers.
¦1 Manifestly, the viewing screens may be mounted at a
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j diferell~ allqle ~r orn t:he ver~ical plane and tne entire unit
¦ may be ~100L- MOUnted Or ceiliny mountcd . Both 51 Lde tr:al~S
par-ellcies an~l motiorl pictures with or without sound effects
may be e~llployed in black an(:l white or. in :~olor on an inter-
miLt nt o~ COllt inuoL~. bas ! ~: .
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