Optical: systems and elements – Lens – With viewed object or viewed field illumination
Reexamination Certificate
1999-10-15
2001-08-28
Mack, Ricky (Department: 2872)
Optical: systems and elements
Lens
With viewed object or viewed field illumination
C359S800000, C359S799000
Reexamination Certificate
active
06282035
ABSTRACT:
This application is based on Japanese Application No. 10-293334, the content of which is hereby incorporated by reference.
FIELD OF THE INVENTION
The present invention is directed generally to an image forming optical system, and, in one aspect, to an image forming optical system for reading and inspection which minimizes the effects of ghosting in an image.
BACKGROUND OF THE INVENTION
In order to read or inspect an object which is imaged by an image forming optical system, it is necessary to illuminate the object. An illuminating optical system is typically constructed as a separate system from the image forming optical system; however, by employing a structure which introduces illuminating light at an intermediate point of the image forming optical system, the overall size of the apparatus can be reduced. Referring to
FIG. 7
, illuminating light
70
is introduced at an intermediate point of an image forming optical system from a light source
72
. The illuminating light
70
is reflected by a reflecting surface (RS), which is a partially-reflecting surface that allows some light to pass through and reflects some light. The reflected light
74
passes through a first lens group (Gr
1
) and a filter (FL), and a portion of the reflected light
74
(ordinary light
76
) is reflected by an object (not shown). The ordinary light
76
passes again through the filter (FL) and the first lens group (Gr
1
). The ordinary light
76
then passes through the reflecting surface (RS), a second lens group (Gr
2
), and falls on an imaging surface (IS) as an image
78
.
As can be seen in
FIG. 8
, some of the reflected light
74
is reflected as an extraordinary component
82
from one or more lens surfaces
80
and reaches the imaging surface (IS) as a ghost
84
before the reflected light
74
reaches the object to be imaged. This situation causes ghosts in the image, which are typically detrimental. The ghosting effect is particularly great when the reflectance of the object being imaged is low.
SUMMARY OF THE INVENTION
The present invention is a new and advantageous image forming optical system which minimizes the effects of ghosting caused by extraordinary light which is reflected from one or more lens surfaces and falls onto an imaging surface. One object of the present invention is to provide an improved image forming optical system. Another object of the present invention is to provide an image forming optical system which minimizes the effects of ghosting even when illuminating light is introduced at an intermediate point of the image forming optical system.
The above-mentioned objects are achieved by embodiments of the present image forming optical system having the structures described hereinafter. An image forming optical system according to a first aspect of the invention illuminates an object to be imaged with illuminating light which is introduced at an intermediate point of the image forming optical system. Means for introducing illuminating light may include, but is not limited to, a reflecting surface disposed within the image forming optical system for reflecting illuminating light, emitted by an external light source, toward the object to be imaged. The reflecting surface may be a mirror which reflects some light components while allowing other light components to pass therethrough. When the image forming optical system is divided into, from an object side, a front lens unit and a rear lens unit at a point where the illuminating light is introduced, the illuminating light passing through the rear lens unit, with the light source image on a diaphragm surface as an object point and with a given surface of the front lens unit as a reflecting surface, satisfies the following condition on an imaging surface of the entire image forming optical system:
Y
ref
Y
max
≥
1.0
wherein
Y
ref
is a maximum luminous flux radius on the imaging surface of the entire image forming optical system of the illuminating light passing through the rear lens unit; and
Y
max
is a maximum image radius.
An image forming optical system according to a second aspect of the invention is an image forming optical system which illuminates an object to be imaged with illuminating light that is introduced at an intermediate point of the image forming optical system. When the image forming optical system is divided into, from an object side, a front lens unit and a rear lens unit at a point where the illuminating light is introduced, a back focal length of the optical system, in which the light source image on a diaphragm surface is an object point, a given surface of the front lens unit is a reflecting surface, and a last surface of the rear lens unit is included, satisfies the following condition:
-
20.0
<
f
bref
f
all
<
0.5
wherein
f
bref
is the back focal length of the image forming optical system; and
f
all
is an overall focal length of the image forming optical system.
A positive back focal length indicates a focal point which is on the imaging surface side of the last surface of the rear lens unit and a negative back focal length indicates a focal point which is on the object side of the last surface of the rear lens unit.
REFERENCES:
patent: 3926500 (1975-12-01), Frosch et al.
patent: 5743612 (1998-04-01), Matsuda et al.
patent: 8-327966 (1966-12-01), None
patent: 4-194921 (1992-07-01), None
Mack Ricky
Minolta Co. , Ltd.
Sidley & Austin
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