Projection screen

Details Projection screen Projection screen

1999-04-16

2001-06-19

Metjahic, Safet (Department: 2858)

Optical: systems and elements

Projection screen

Unitary sheet comprising plural refracting areas

Reexamination Certificate

active

06249376

ABSTRACT:

TECHNICAL FIELD
The present invention relates to a projection screen, and, more particularly, to a projection screen so made that especially a moiré pattern which is produced due to the cyclic structure of a Fresnel lens and that of lenticular lenses will be obscure.
BACKGROUND ART
In projection televisions or projection screens for projectors, which are a combination of a Fresnel lens and lenticular lenses, a moiré pattern that is produced due to a group of concentric circles on the Fresnel lens and a group of parallel straight lines of the lenticular lenses is known to be either elliptical or hyperbolic depending on the pitch ratio between these two groups (see U.S. Pat. No. 2,567,654).
FIG. 6
is a view showing one example of the moiré pattern in the shape of an ellipse (hereinafter also referred to simply as “elliptical moiré”); and
FIG. 7
is a view showing one example of the moiré pattern in the shape of a hyperbola (hereinafter also referred to simply as “hyperbolic moiré”). In
FIG. 6
, the elliptical moiré is such that its focal point corresponds to the center of the Fresnel lens. Further, in
FIG. 7
, the asymptotic lines of the hyperbolic moiré are those two lines that cross each other at the center of the Fresnel lens. It is noted that the angle formed with these asymptotic lines varies depending on the pitch ratio between the lenticular lenses and the Fresnel lens.
In many cases, perceived by an observer is generally either one of the moiré patterns of these two types. In practice, however, the moiré patterns of these two types are simultaneously produced. When the pitch ratio between the lenticular lenses and the Fresnel lens is n+0.5 (n: integer), the intensities of the moiré patterns of the two types become lowest, and the cycles (pitches) of these moiré patterns become identical (see Japanese Patent Laid-Open Publication No. 52985/1981). Even if the pitch ratio between the lenticular lenses and the Fresnel lens only slightly deviates from n+0.5, the cycles (pitches) of the two moiré patterns do not agree with each other, and a secondary moiré pattern is produced by the moiré patterns of these two types. This secondary moiré pattern is scalelike, and produced on the transverse axis of the lenticular lenses in the repeating direction.
This secondary moiré pattern is minimized when the pitch ratio between the lenticular lenses and the Fresnel lens is in the vicinity of n+0.4, or of n+0.6 (see Japanese Patent Publications No. 68365/1991 and No. 72972/1991). However, when the pitch ratio between the lenticular lenses and the Fresnel lens is in the vicinity of n+0.4, or of n+0.6, the intensity of the primary moiré pattern (elliptical moiré or hyperbolic moiré) will not become so low. In the conventional projection screens, the pitch of the lenticular lenses is approximately 0.7 to 1.0 mm, and that of the Fresnel lens is approximately 0.1 to 0.15 mm, so that the pitch of the primary moiré pattern (elliptical moiré or hyperbolic moiré) which varies relative to the pitch of the lenticular lenses becomes relatively large. For this reason, the conventional projection screens have such a problem that the primary moiré pattern (elliptical moiré or hyperbolic moiré) tends to become conspicuous due to the size of its pitch.
SUMMARY OF THE INVENTION
On the other hand, it has recently become possible to successfully produce highly minute projection screens, and there is even such a case where the pitch of the lenticular lenses is made 0.2 mm or less. In this case, if the pitch of the Fresnel lens is approximately 0.1 to 0.15 mm, the pitch of the lenticular lenses and that of the Fresnel lens become close to each other (that is, the integer part (n) of the pitch ratio becomes 1 or 2), and the intensities of both the primary and secondary moiré patterns become high. It is noted that there is the following problem in this case: regarding the primary moiré pattern, the pitch thereof becomes small, so that this pattern becomes obscure; on the contrary, with respect to the secondary moiré pattern, the pitch thereof is to have such a size that this pattern will be conspicuous.
The present invention was accomplished in the light of the foregoing. An object of the present invention is to provide a projection screen comprising lenticular lenses and a Fresnel lens in combination, in which both primary and secondary moiré patterns will never be conspicuous even when the pitch of the lenticular lenses is made fine.
The present invention provides a projection screen comprising a Fresnel lens and lenticular lenses in combination, wherein, when the pitch of the lenticular lenses is indicated by p
L
, and the pitch of the Fresnel lens is indicated by p
F
, and when p
E
and p
H
are defined as follows: in the case where p
L
>p
F
,
p
E
=1.0/(1.0/p
F
−[p
L
/p
F
]/p
L
)  (i)
p
H
=1.0/(1.0/p
L
−1.0/p
F
+[p
L
/p
F
]/p
L
)  (ii), and
in the case where p
F
>p
L
,
p
H
=1.0/(1.0/p
L
−[p
F
/p
L
]/p
F
)  (iii)
p
E
=1.0/(1.0/p
F
−1.0/p
L
+[p
F
/p
L
]/p
F
)  (iv)
([X]: the integer part of X),
the relationship
p
E
/p
H
≧2.4 or p
H
/p
E
≧2.4
is fulfilled.
In the present invention, it is preferable that p
E
and p
H
also fulfill the following relationship:
MAX (p
E
, p
H
)<1.5 mm.
According to the present invention, since the pitches p
E
and p
H
of the elliptical moiré and hyperbolic moiré which are produced by the cyclic structure of the lenticular lenses and that of the Fresnel lens fulfill the above-described relationship, both the primary and secondary moiré patterns will never be conspicuous even when the pitch of the lenticular lenses is made fine, and a projected image can be observed clearly.


REFERENCES:
patent: 2567654 (1951-09-01), Siezen
patent: 4725134 (1988-02-01), Ogino
patent: 5177637 (1993-01-01), Tsukada
patent: 56-052985 (1981-05-01), None
patent: 3 683 65 (1982-11-01), None
patent: 3 729 72 (1984-01-01), None
patent: 59-095525 (1984-06-01), None
patent: 60-263932 (1985-12-01), None
patent: 62-236282 (1987-10-01), None
patent: 3-149540 (1991-06-01), None
patent: 7-128743 (1995-05-01), None
patent: 8-101459 (1996-04-01), None

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