Zone focusing optical system

A compact zone focusing lens system is provided for use as a photographic camera objective. In the system, a positive meniscus lens is mounted in registration with the larger opening of a truncated, opaque, open-ended cone section the apical end of which serves as a maximum system aperture stop. A transparent disk having a plurality of meniscus lens elements integrally molded therein is mounted so that its lens elements can be selectively rotated into alignment with the cone section apical opening to provide system focal lengths which are appropriate for sharply focusing objects located within different object distance ranges.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention in general relates to photographic optical systems and in 
particular to a zone focusing optical system particularly suitable for use 
in a camera of the type which includes an automatic ranging and focusing 
arrangement. 
2. Description of the Prior Art 
According to the well-known Gaussion lens equation, an image of an object 
which is located ahead of an optical system will only be sharply formed on 
film located behind the optical system when the distance between the 
optical system and the focal length of the system is correct. Since the 
location of film in photographic cameras is typically fixed, this means 
that sharpest imaging at a given object distance requires a unique focal 
length or a unique optical system to film distance. The process of 
adjusting the optical system focal length, or the optical system to film 
distance, to achieve maximum image sharpness at different object distances 
is known as focusing and may be accomplished in well-known ways. One way 
of focusing, for example, is to provide a lens of fixed focal length in 
combination with a means for adjusting the spacing between the lens and 
film as a function of object distance. The usual arrangements for 
accomplishing this involve the use of a flexible bellows connecting the 
lens mount to the film retaining housing and a linkage for extending the 
bellows to alter the spacing between the optical system and film. 
Another known focusing arrangement utilizes a variable focus optical system 
fixed in place ahead of the film. Here the lens focal length is changed 
with object distance by changing the air spacing between individual 
elements of the lens, usually by moving a front cell of the lens with 
respect to other elements or an element. 
Another known focusing arrangement suitable for use with fixed lens to film 
distance situations involves the use of a rotatable lens turret which 
carries a plurality of lenses having different focal lengths each of which 
can be rotated into place along the camera taking path. These arrangements 
can be classified as zone focusing systems because they do not provide a 
continuously variable focal length but rather provide discrete focal 
lengths which sharply image for particular object distances and more or 
less sharply image objects located on either side of that object distance 
most appropriate for the particular lens focal length. In this manner, 
such systems provide adequate sharpness over a range or "zone" of object 
distances relying on the assumption that for any given focal length there 
exists a blur, due to defocus, of small enough size such that the 
performance of the system will not be adversely affected provided that the 
object remains in the appropriate zone. An example of such a system is 
shown and described in, for instance, U.S. Pat. No. 3,418,908 issued to 
Edwin H. Land on Dec. 31, 1968 and entitled "Range Finding-Focusing 
Apparatus For A Photographic Camera". 
It is also known to provide zone focusing arrangements by combining a fixed 
lens with a turret having lenses which can be selectively indexed into 
alignment with the fixed lens such that combinations of the fixed lens 
with individual turret lenses provide a series of different focal lengths. 
One such arrangement which utilizes a fixed doublet is described in U.S. 
Pat. No. 494,128 issued to Erskine Decker on Mar. 28, 1893 and entitled 
"Lens For Cameras". 
Of the three focusing arrangements described, the first two have the 
advantage of continuous adjustability over a range of object distances. 
However, for a particular application this advantage must be evaluated in 
view of the increased cost associated with the need for bellows extension 
arrangements or more complex multi-element lens systems. Zone focusing 
systems, while not offering the continuous adjustability feature, are 
often adequate and offer an attractive alternate because they can 
generally be made less expensively, than the others. However, most known 
zone focusing systems are somewhat cumbersome, requiring a large amount of 
space because of their turret arrangements. Therefore, it is a primary 
object of the present invention to provide a zone focusing system which is 
inexpensive, compact and easy to manufacture. 
It is another object of this invention to provide a zone focusing optical 
system that is particularly suitable for use with a camera of the type 
which includes a sonar ranging system and an arrangement for automatically 
positioning a lens disk as a function of select object distances. 
Other objects of the invention in part will be obvious and in part will 
appear hereinafter. The invention accordingly comprises the apparatus 
possessing the construction, combination of elements, and arrangement of 
parts which are exemplified in the following detailed description. 
SUMMARY OF THE INVENTION 
This invention generally relates to photographic optical systems and 
specifically to a zone focusing optical system which is particularly 
suitable for use in camera apparatus of the type which includes an 
automatic ranging and focusing arrangement by which a lens disk can be 
selectively indexed by rotation; and means for facilitating the 
positioning of film on a plane in which it may be exposed and for 
providing a path of predetermined length along which light can be directed 
through an entrance aperture thereof toward the film plane. 
The zone focusing optical system of the invention comprises means for 
defining an opaque housing structured to admit light from a scene into the 
apparatus light path entrance. The housing includes an open-ended section 
having spaced apart inlet and outlet apertures optically aligned with 
respect to one another and with the apparatus light path entrance along an 
axis which extends through the center of the apparatus light path 
entrance. Included in the open-ended section are intermediate opaque 
convergent portions, which connect the inlet and outlet apertures thereof, 
for excluding light from entering the housing. The outlet aperture is 
positioned adjacent the apparatus light path entrance and is spaced 
forwardly thereof by a predetermined distance. 
Also included is a prime lens of predetermined positive power. The prime 
lens is mounted in optical registration with the inlet aperture and is 
structured to refract all the chief rays from all image forming bundles of 
rays which originate from a predetermined object distance, less than 
infinity, from the prime lens so that such chief rays pass through the 
center of the outlet aperture and are imaged over the film plane. 
Additionally included is a lens disk which has a plurality of angularly 
spaced apart light refracting zones each of which is structured to 
optically cooperate with the prime lens to in combination therewith image 
an object at a different distance from the prime lens than the 
predetermined object distance for which the prime lens is structured. 
The lens disk, which is preferably molded of a transparent optical plastic, 
is mounted behind the outlet aperture in the predetermined space between 
the outlet aperture and the apparatus light path entrance for rotation 
such that each light refracting zone thereof can be selectively indexed 
into optical registration with the outlet aperture. The outlet aperture 
operates to define the active light refracting area of each of the light 
refracting zones of the lens disk and to define a maximum aperture stop 
for each of the light refracting zones in combination with the prime lens.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
In its preferred embodiment, the zone focusing optical system of the 
present invention is shown as part of a virtually fully automatic type 
camera which utilizes self-processable type film and which is designated 
generally at 10 in FIG. 1. Although shown incorporated in the camera 10, 
it is to be understood that the optical system of the invention, which is 
designated generally at 22 in FIG. 2, is not limited in use to only those 
types of photographic apparatus represented by the camera 10. However, as 
will be discussed below, the camera 10 does have certain features which 
make the invention at least in part particularly suitable for use with it. 
As best seen in FIG. 1, the camera 10 is a rigid, non-folding body type 
which includes a generally prismatic shaped major housing 12, a generally 
L-shaped front housing 14, and a generally rectangularly-shaped film 
loading door 16 which collectively define its outward appearance and serve 
to house and protect its interior components. The aforementioned housings, 
12 and 14, and the film loading door 16 are all preferably molded of an 
opaque plastic to preclude unwanted light from entering the camera 
interior. 
The base of the prismatic housing 12 is adapted in a well-known manner to 
releasably receive and hold a film cassette 18 in which is disposed a 
stacked array of self-processable film units, each of which is processed 
by the camera 10 in a well-known manner after photoexposure, and a flat, 
thin battery which is positioned underneath the array of film units 
(neither shown). The film cassette battery is used to supply power to 
operate the various electrical components of the camera 10. An example of 
such film cassettes is described in considerable detail in U.S. Pat. No. 
3,872,487 issued to Nicholas Gold on Mar. 18, 1975 and entitled 
"Photographic Film Assemblage and Apparatus" and of such film units in, 
for example, U.S. Pat. Nos. 3,415,644; 3,594,165 and 3,761,268. Thus, the 
camera 10 is provided with means for facilitating the positioning of film 
in a plane in which it can be exposed. 
As best seen in FIG. 2, the zone focusing optical system 22 is arranged 
along an optical axis, OA, intermediate an opening 20 (FIG. 1), which is 
located in a vertical forward wall 21 of the L-shaped housing 14 and which 
faces the scene to be photographed, and an entrance aperture 26 located in 
an opaque exposure chamber 24 (partly shown) which is positioned in a 
well-known manner inside the prismatic shaped housing 12 and also has a 
generally prismatic shape. 
Located within the exposure chamber 24 is a trapezoidal-shaped mirror 54 
(FIGS. 1 and 2) that is arranged at a predetermined angle with respect to 
the optical axis, OA, and the camera film plane to provide a folded light 
path of predetermined length therebetween along which image forming scene 
rays from the zone focusing optical system 22 travel to the film within 
the cassette 18 during a camera exposure cycle. The exposure chamber is of 
the type which is described in considerable detail in U.S. Pat. No. 
4,057,815 issued to Bruce K. Johnson on Nov. 8, 1977 and entitled 
"Anti-Flare Structure For Photographic Optical System". 
Film exposure is regulated by a well-known automatic exposure control 
system which operates to control the amount of exposure delivered to the 
film by selectively controlling the movement of a shutter blade mechanism 
generally designated at 28 in FIG. 1. The blade mechanism 28 comprises a 
pair of counter reciprocating blades, 30 and 32, each of which includes an 
aperture, 34 and 36 respectively, that are made to overlap one another to 
provide a preprogrammed set of aperture values and shutter speeds over the 
entrance aperture 26 to the camera light path. The blades, 30 and 32, are 
situated immediately forward of the camera light path entrance aperture 26 
for this purpose and are of the type more fully described in U.S. Pat. No. 
3,942,183 issued to George D. Whiteside on Mar. 2, 1976 and entitled 
"Camera With Pivoting Blades". 
The exposure control system of the camera 10 operates in either an ambient 
mode in which available light provides the source for illuminating the 
scene or in an artificial light source mode in which an electronic strobe 
light 38 (FIG. 1), which forms a permanent part of the camera 10, serves 
as the scene illumination source. 
Also provided in the camera 10, but not shown, is a well-known ultrasonic 
ranging system which operates on well-known principles. Ultrasonic energy 
is transmitted by the system toward a subject to be photographed and is 
thereafter reflected by the subject back toward the camera 10. 
Characteristics of the transmitted and received signals are then compared 
to derive a control signal representative of the subject distance. The 
control signal is thereafter utilized to drive a lens disk 56 which forms 
part of the zone focusing optical system 22. The lens disk 56 is 
preferably driven by the arrangement shown and described in U.S. Pat. No. 
4,167,316 issued to Bruce K. Johnson et al. on Sept. 11, 1979 and entitled 
"Sonar Controlled Lens Focus Apparatus" the contents of which are 
specifically incorporated herein by reference as a "means for 
automatically indexing the lens disk 56 between angular positions". 
Although reference should be had to the aforementioned U.S. Pat. No. 
4,167,316 for complete details, the lens arrangement described therein 
comprises a plurality of lens elements mounted for displacement between a 
plurality of focal positions by a lens holding disc member disposed for 
rotation about a fixed center axis. The plurality of lens elements in the 
'316 patent are disposed in the lens holding disc member in 
circumferentially spaced-apart relation with respect to each other about 
the disc center axis. A scanning shutter blade arrangement similar to the 
blade apparatus 28 herein includes a walking beam to which the shutter 
blades are pivotally attached for movement thereby. The walking beam is 
pivotally disposed to impact upon an actuator member which, in turn, 
operates by way of a torsion spring to impact the lens holding disc member 
and thereby rotate the lens holding disc member so as to sequentially move 
each of its lens elements into their respective focal position. 
One of the requirements for the above described sonar controlled lens 
focusing apparatus is that the lens disc which is to be used therewith 
must be of low inertia so that it can be properly driven by the lens disk 
actuator and also preferably will be as compact as possible so that the 
size of the system will be at a minimum. The lens disk 56 of the zone 
focusing optical system 22 of the invention satisfies these requirements 
as well as that of providing, in combination with the other components of 
the optical system 22, an inexpensive means of focusing the camera 10 so 
as to provide a well-corrected photographic image at the camera film plane 
for photographic subjects whose distance from the camera 10 can range from 
24 inches to infinity. As will be seen from the description to follow, the 
zone focusing optical system 22 satisfies these requirements by providing 
a useful image that covers a semi-field angle of substantially 27 Deg. at 
an f-number of 10. 
The structure and optical performance of the optical system 22 will best be 
understood by referring now to FIG. 2 wherein the optical system 22 can be 
seen to comprise an opaque housing section 42 which cooperates in a 
well-known manner with the prismatic-shaped housing 12 and the L-shaped 
housing 14 to enclose, protect and support various camera components. 
Included in the housing section 42 is an open-ended section 44 that is 
structured to admit light from a scene through the camera light path 
entrance aperture 26. For this purpose the open-ended section 44 has inlet 
aperture 46 and an outlet aperture 48 both of which are optically aligned 
along the optical axis, OA, with respect to one another and with the 
camera light path entrance aperture 26. Connecting the inlet and outlet 
apertures, 46 and 48, are intermediate convergent wall portions for 
excluding light from entering the camera housing and those portions are 
provided with internal serrations 50 which extend transverse to the 
optical axis, OA, and operate to intercept stray radiation thereby 
reducing the effects of unwanted or glare light. The open-ended section 44 
as can be seen is a funnel-like section preferably shaped in the form of a 
truncated right quadrangular pyramid with the apertures, 46 and 48, 
thereof lying in planes corresponding to the bases of the pyramid and 
wherein the intermediate connecting portions thereof correspond to the 
sides of the pyramid. 
The open-ended section outlet aperture 48 is positioned adjacent the camera 
light path entrance aperture 26 and is spaced forwardly thereof to provide 
a predetermined space for the blades, 30 and 32, and the lens disk 56. 
Mounted in optical registration with the open-ended section inlet aperture 
46 is a prime positive meniscus lens 52. The meniscus lens 52 is optically 
structured, preferably from an optical plastic, to refract all the chief 
rays from all image forming bundles of rays originating at a predetermined 
object distance, less than infinity, from it so that those chief rays pass 
through the center of the open-ended section outlet aperture 48 and are 
imaged over the plane in which the film resides. 
To provide its optical function, the meniscus lens 52 has an index, 
n.sub.d,=1.492; an Abbe number, V,=57.2; front and rear surface basic 
vertex radii, R.sub.F =0.775 and R.sub.R =1.185 inches respectively; an 
axial thickness, t,=0.125 inches. The rear surface of the meniscus lens 52 
is aspheric and is described by the following formula: 
##EQU1## 
wherein Z represents the distance of a point on the aspheric surface 
measured from a reference plane perpendicular to the system optic axis, 
OA, and passing through the rear vertex of the lens 52 and y is the radial 
distance of the point away from the optic axis, OA. The aspheric rear 
surface of the meniscus lens 52 is structured primarily to correct the 
meniscus lens 52 for off-axis aberrations. With the foregoing structure, 
the meniscus lens 52 has an effective focal length of 4.144 inches (9.5 
diopters) and, by itself, has the performance, in terms of field sags and 
RMS blur, indicated respectively in FIGS. 3 and 4 which will discussed 
further hereinafter. 
The size of the cone of energy that reaches the camera film plane is 
defined by the joint action of the aperture 48 and the aperture defined by 
the blades 30 and 32. When the aperture defined by the blades, 30 and 32, 
is a maximum, either the aperture 48 or the aperture defined by the 
blades, 30 and 32, can be considered to be the aperture stop of the system 
22, but when the aperture defined by the blades, 30 and 32, is smaller 
than that provided by the aperture 48, then the aperture defined by the 
blades, 30 and 32, can be considered to be the system aperture stop. The 
aperture 48 (FIG. 2) is spaced behind the meniscus lens 52 by a distance, 
S.sub.1, measured from the meniscus rear surface vertex, of 0.369 inches 
and has a diameter of 0.372 inches. 
The lens disk 56 is mounted for rotation in a well-known manner about a hub 
58 thereof and includes a plurality of angularly spaced apart meniscus 
lens elements or light refracting zones indicated as the Roman numerals I 
through IV as shown in FIG. 1 and in part in FIG. 2. The rotational 
mounting arrangement of the lens disk 56 permits its meniscus elements, I 
through IV, to be selectively aligned in registration with and immediately 
behind the aperture 48. 
Each of the lens disk meniscus elements, I through IV, is optically 
structured to operate in combination with the prime meniscus lens 52 to 
provide the system 22 with a plurality of effective focal lengths, 
different from one another, for focusing at different photographic subject 
distances. Lens I combines with the meniscus lens 52 to provide a combined 
focal length that best focuses objects located at 3.0 ft. with a subject 
range from 24 to 48 inches; lens II combines with the meniscus 52 to best 
focus objects located at 5.6 ft. with a subject range from 48 to 100.8 
inches; lens III combines with the meniscus 52 to best focus objects at 
12.6 ft. with a subject range from 100.8 to 201.6 inches; and lens IV and 
the meniscus 52 best focus objects at 50.0 ft. with a subject range from 
201.6 inches to infinity (see FIGS. 5, 7, 9 and 11). 
Each of the lens disk meniscus elements, I through IV, is also provided 
with at least one aspheric surface that is structured primarily to 
favorably correct residual spherical aberrations of the prime meniscus 
lens 52. 
The lens disk meniscus elements, I through IV, have the characteristics 
represented by the following tabulated data which refers to FIG. 2. 
______________________________________ 
Lens n.sub.d 
V Radii (in) 
t (in) 
S.sub.2 (in) 
EFL (in) 
______________________________________ 
I 1.592 30.8 R.sub.1 = -2.0 
.0562 
.0793 29.974 
(3.0 ft) R.sub.2 = -1.825 
II 1.592 30.8 R.sub.3 = -10.0 
.0553 
.0712 128.71 
(5.6 ft) R.sub.4 = -8.695 
III 1.592 30.8 R.sub.5 = -10.0 
.0549 
.0712 -413.9 
(12.6 ft) R.sub.6 = -10.506 
IV 1.592 30.8 R.sub.7 = -10.0 
0.547 
0.0712 
-106.7 
(50.0 ft) R.sub.8 = -12.016 
______________________________________ 
wherein n.sub.d is the index of refraction, V is the Abbe number, R.sub.1, 
R.sub.2 . . . R.sub.8, represent basic radii of surfaces, t is the axial 
thickness, and S.sub.2 is the axial distance from the aperture 48 to the 
vertex of a respective element; EFL is effective focal length; and wherein 
the front surface of element I is an aspheric surface described by the 
formula: 
##EQU2## 
and elements II, III and IV all have aspheric front surfaces described by 
the formula: 
EQU Z=-0.05y.sup.2 -0.151589y.sup.4 +0.824884y.sup.6 
the Z in all of the foregoing aspheric formulas representing the distance 
of a point on the aspheric surface measured from a reference plane 
perpendicular to the system optic axis and through the vertex of a 
respective optical element and y is the radial distance of the point away 
from the optic axis. 
The lens disk 56 and the meniscus lens elements, I through IV, are 
preferably integrally molded of a transparent optical plastic and the 
aperture 48, being spaced forward of each lens disk meniscus, provides a 
masking function by defining the active refracting area of each lens disk 
meniscus element when such an element is brought into registration with 
the aperture 48. 
Moreover, as illustrated in FIG. 2, the clear openings of the converging 
section inlet aperture 46 and aperture 48, and the spacing separating them 
are selected so that the usable refracting area of the prime meniscus lens 
52 exceeds the usable refracting area of each of the lens disk meniscus 
elements, I through IV, by as much as optical considerations permit in 
order to minimize the overall space requirements for the lens disk 56. In 
the preferred embodiment, the prime meniscus refracting area is 
approximately 4.16 times larger than each lens disk meniscus element 
refracting area thus permitting the lens disk 56 to be quite small and of 
low inertia. 
Referring now generally to FIGS. 3-12, there are shown a series of graphs 
which represent the results of well-known computer generated spot diagrams 
for the prime meniscus lens 52 with and without the lens disk meniscus 
elements, I through IV, as those elements are described in the above 
tabular data. Each curve is plotted from spot diagrams for theoretical 
object point sources on-axis, at 0.4, 0.7, and full field (1.0=27 Deg.). 
Each spot diagram is produced by 300 rays traced in three colors (100 in 
each color and with C, D and F lines given equal weighting) with each ray 
originating at one of the point sources and landing on a reference plane 
coincident with the camera film plane. 
FIG. 4 shows the RMS (Root Mean Square) blur of the prime meniscus lens 52 
operating by itself at f-numbers of f/10 defined by the apertures 48 and 
26 and f/14 which can be provided by the blades 30 and 32. 
RMS blur corresponds to the circle of confusion and represents the combined 
effect of all aberrations except distortion. RMS blur is calculated in a 
well-known manner by first determining the centroid of the spot diagram 
and then the length of vectors drawn from the spot diagram centroid to 
each spot, the point where the ray lands in a reference plane. The 
root-mean-square magnitude of the vectors is then calculated to yield the 
RMS blur, a radius. If the reference plane is the camera film plane, as 
here, and the film is flat, blur will become visible at an RMS blur value 
of 0.0018 inches which corresponds to the conventional circle of confusion 
diameter of 0.005 inches. An RMS blur radius of 0.005 inches or less is 
desirable for optimum photographic image quality, particularly within the 
0.7 angular field limit where most of the photographic subject is usually 
found, but RMS blur values in excess of 0.005 inches can be tolerated 
outside the 0.7 angular field limit. On this basis, the meniscus lens 52 
could not be used by itself at f/10 but could be used at f/14 (see FIG. 
4). 
FIG. 3 represents the field sag of the meniscus lens 52 again, by itself, 
at f-numbers of f/10 and f/14. Each graph describes the field coverage of 
the lens, its astigmatism and its state of focus. Sagittal points on the 
graphs are connected with dash and dot lines; tangential points are 
connected with dash lines. The combined effects of all aberrations, except 
distortion, from the reference plane is the RMS blur graph plotted with 
solid lines. The solid line is the best RMS image surface or, in other 
words, the locus of the circle of least confusion in the RMS sense. The 
vertical axis of FIG. 3 is the same as the horizontal axis of FIG. 4. The 
horizontal axis of FIG. 3 represents axial displacement of the RMS blur 
away from the reference plane. 
FIGS. 6, 8, 10 and 12 represent the RMS blur for each of the lens disk 
meniscus elements I through IV in combination, respectively, with the 
prime meniscus lens 52 and RMS blur was calculated as described above for 
best focus and for two other focus distances corresponding to the subject 
distance range for the particular combination. 
FIGS. 5, 7, 9 and 11 show the field sags for each of the lens disk meniscus 
elements I through IV in combination, respectively, with the prime 
meniscus lens 52. 
FIGS. 13-15 represent the RMS blur for the 3 ft. lens disk meniscus, 
element I, in combination with the prime meniscus 52 at the focus 
distances indicated and as a function of f-number. Similarly, FIGS. 16-18 
represent the RMS blur for the 5.6 ft. lens disk meniscus, element II, in 
combination with the prime meniscus 52. 
Although the RMS blur performance for the optical system 22 is somewhat 
degraded, i.e., above a 0.005 circle of confusion, at semifield angles 
greater than 0.7 of full field when operating at an f-number of f/10, the 
exposure control system of the camera 10 is preferably programmed so that 
the blades, 30 and 32 (see FIG. 2), under both ambient and artificial 
light source exposure modes and in all but extreme exposure conditions, 
like very low available light in the ambient mode or far subject distances 
in the artificial light source illumination mode, define f-numbers larger 
than f/10. Under normal scene illumination conditions the optical system 
22 will not operate at f/10 and therefore the RMS performance beyond the 
0.7 semi-field angle is not a significant consideration for most purposes 
likely to be encountered. 
Certain changes may be made in the above-described embodiment without 
departing from the scope of the invention, and those skilled in the 
optical arts may make still other changes according to the teachings of 
the disclosure. For example, the size of the optical system 22 may be 
scaled up or down in a well-known manner so long as the changes in optical 
performance which attend such scale changes do not exceed the allowable 
limits for the particular photographic application. Therefore, it is 
intended that all matter contained in the above description or shown in 
the accompanying drawings shall be interpreted as illustrative and not in 
a limiting sense.