Optical: systems and elements – Lens – With reflecting element
Reexamination Certificate
2002-01-14
2004-08-31
Sugarman, Scott J. (Department: 2873)
Optical: systems and elements
Lens
With reflecting element
C359S726000, C359S720000
Reexamination Certificate
active
06785060
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to optical systems of reflecting type and image pickup apparatuses using the same and, more particularly, to such optical systems which, using an optical element of many reflecting surfaces, form an object image on a predetermined plane. Still more particularly, this invention relates to improvements of the compact form of the entirety of the optical system suited to video cameras, still cameras or copying machines.
2. Description of the Related Art
There have been many previous proposals for utilizing the reflecting surfaces of convex and concave mirrors in the optical system for an image pickup apparatus.
FIG. 24
schematically shows a so-called mirror optical system composed of one concave mirror and one convex mirror.
In the so-called mirror optical system of
FIG. 24
, an axial beam
104
coming from an object is reflected from the concave mirror
101
. While being converged, it goes toward the object side and is then reflected by the convex mirror
102
to form an image on an image plane
103
.
This mirror optical system is based on the configuration of the so-called Cassegrainian reflecting telescope. The aim of adopting it is to shorten the total length of the entire system as the equivalent telephoto system which is constructed with refracting surfaces or lenses alone has a long total length. To this purpose, the optical path is folded twice by using two reflecting surfaces arranged in confronting relation.
Even for the objective lens systems of telescopes, besides the Cassegrainian type, there are known, from a similar reason, a large number of forms with the use of a plurality of reflecting mirrors in shortening the total length of the optical system.
Like this, in a case where a photographic lens would take a long total length, it has been the common practice to employ reflecting mirrors instead of some of the lens members. By folding the optical path to good efficiency, a compact mirror optical system is obtained.
However, the Cassegrainian reflecting telescopes and like mirror optical systems generally suffer a problem due to the vignetting effect by the convex mirror
102
, as the object light beam is partly mutilated. This problem will exist so long as the convex mirror
102
is laid at the central passage of the object beam
104
.
To solve this problem, the reflecting mirror may be decentered, thus avoiding obstruction of the passage of the object beam
104
by the unintegrated part of the optical system. In other words, the principal ray
106
of the light beam is dislocated away from an optical axis
105
. Such an optical system, too, has previously been proposed.
FIG. 25
is a schematic diagram of a mirror optical system disclosed in U.S. Pat. No. 3,674,334, wherein the problem of mutilation described above is solved in such a way that the reflecting mirrors to be used are rotationally symmetric with respect to the optical axis and partly cut off.
The mirror optical system of
FIG. 25
comprises, in order of passage of the light beam, a concave mirror
111
, a convex mirror
113
and a concave mirror
112
, which, when in the prototype design, are, as shown by the double dot-and-dash lines, the complete reflecting surfaces of rotational symmetry with respect to the optical axis
114
of these, the concave mirror
111
is used only in the upper half on the paper of the drawing with respect to the optical axis
114
, the convex mirror
113
only in the lower half and the concave mirror
112
only in a lower marginal portion, thereby bringing the principal ray
116
of the object beam
115
into dislocation away from the optical axis
114
. The optical system is thus made free from the mutilation of the object beam
115
.
FIG. 26
shows another mirror optical system which is disclosed in U.S. Pat. No. 5,063,586. The reflecting mirrors have their central axes made themselves to decenter from the optical axis. As a result, the principal ray of the object beam is dislocated from the optical axis, thus solving the above-described problem.
Referring to
FIG. 26
, assume that the perpendicular line
127
to the object plane
121
is an optical axis. With a convex mirror
122
, a concave mirror
123
, a convex mirror
124
and a concave mirror
125
in order of passage of the light beam, it is then proven that the centers of their reflecting areas do not fall on the optical axis
127
and that their central axes (the lines connecting those centers with the respective centers of curvature of the reflecting surfaces)
122
a
,
123
a
,
124
a
and
125
a
are decentered from the optical axis
127
. In connection with this figure, the decentering amount and the radius of curvatures of every one surface are appropriately determined to prevent the object beam
128
from being mutilated by the other mirrors. Thus, an object image is formed on a focal plane
126
with high efficiency.
Besides these, U.S. Pat. Nos. 4,737,021 and 4,265,510 even disclose similar systems freed from the vignetting effect either by using certain portions of the reflecting mirrors of revolution symmetry about the optical axis or by decentering the central axes themselves of the reflecting mirrors from the optical axis.
These reflecting type photographic optical systems, because they have a great number of constituent parts, require highly precise assembly of the individual optical parts to insure satisfactory optical performance. In particular, because the tolerance for the relative positions of the reflecting mirrors is severe, later adjustment of the position and angle of orientation of each reflecting mirror is indispensable.
To solve this problem, one of the proposed methods is to construct the mirror system in the form of, for example, a block, thus avoiding the error which would otherwise result from the stepwise incorporation of the optical parts when in assembling.
It has been known to provide one block with a large number of reflecting surfaces. For example, the viewfinder systems employ optical prisms such as pentagonal roof prisms or Porro prisms.
These prisms are made by molding techniques to unify the plurality of reflecting surfaces. Therefore, all the reflecting surfaces take their relative positions in so much good accuracy as to obviate the necessity of adjusting the positions of the reflecting surfaces relative to one another. However, the main function of these prisms is to change the direction of travel of light for the purpose of inverting the image. Every reflecting surface is, therefore, made to be a flat surface.
For the counterpart to this, there is also known an optical system by giving curvature to the reflecting surface of the prism.
FIG. 27
is a schematic diagram of the main parts of an observing optical system disclosed in U.S. Pat. No. 4,775,217. This optical system is used for observing the external field or landscape and, at the same time, presenting an information display of data and icons in overlapping relation on the landscape.
The rays of light
145
radiating from the information display device
141
are reflected from a surface
142
, going to the object side until they arrive at a half-mirror
143
of concave curvature. The reflected ones of the light rays
145
from the half-mirror
143
are nearly collimated by the refractive power of the concave surface
143
, and refract in crossing the surface
142
, reaching the eye
144
of the observer. The observer views an enlarged virtual image of the displayed data or icons.
Meanwhile, a light beam
146
from an object enters at a surface
147
which is nearly parallel with the reflecting surface
142
, and is refracted by it and arrives at the concave surface
143
. Since this surface
143
is coated with a half-permeable layer by the vacuum evaporation technique, part of the light beam
146
penetrates the concave surface
143
and refracts in crossing the surface
142
, entering the pupil
144
of the observer. So, the observer views the display image in overlapping relation on the external field or landscape.
FIG. 28
is a schemat
Akiyama Takeshi
Araki Keisuke
Kimura Ken-ichi
Kurihashi Toshiya
Nanba Norihiro
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