Lens attchment for forming wide-ranging images

The invention provides a lens attachment adapted for use as a supplemental attachment to optical instruments, such as cameras, enlargers, when they are employed to form wide-ranging images upon a wide screen for example. According to the invention, the lens attachment comprises a master lens having focal length f.sub.M and a front member having focal length f.sub.A and a rear member having focal length f.sub.B, each member including cylindrical lenses, said front member and said rear member as a whole being located in front of said master lens, wherein said f.sub.B satisfies: 4f.sub.M .gtoreq..vertline.f.sub.B .vertline..gtoreq.2f.sub.M In addition, the lenses are readily combined on a mount in fitting relationship with the use of tenons and recesses adapted to receive said tenons, thereby securing precise centering of the lenses. Thus, the distance between the rear member and the master lens is extremely shortened, and the diameters of both lenses are made substantially equal.

FIELD OF THE INVENTION 
The present invention relates to a lens attachment used for optical 
instruments, such as photograph camera, motion-picture cameras, 
motion-picture projectors and enlargers, when they are employed to form 
wide-ranging images like those on a cinemascope. 
DESCRIPTION OF THE PRIOR ART 
When a main lens or lenses of an ordinary type (hereinafter referred to as 
the master lens) having a projective range of 6.degree. to 7.degree. is 
employed to form wide-ranging images upon a cinemascope for example, the 
common practice is to attach an extra lens unit to the master lens, the 
extra lens unit being commonly called a converter (hereinafter referred to 
as the converter). The converter consists of cylindrical lenses capable of 
forming horizontally widened images. 
In such cases, however, the converter cannot be directly attached to the 
master lens because of the large effective diameter and weight of its rear 
member, thereby requiring the converter to be mounted on a special fixture 
adapted to be secured to the main instrument body by screws. Under this 
arrangement, a high degree of skill is required for securing precise 
centering of the lenses. In addition, attaching and detaching are 
time-consuming labor. To solve the difficulty of securing precise 
centering of the lenses through the converter to the master lens, it is 
previously arranged in the converter that each focal length of the front 
and rear members is relatively large; however, this means that the lenses 
in each member are accordingly spaced, thereby resulting in an increased 
effective diameter of the lenses. Thus, the converter as a whole 
unavoidably becomes large and heavy. 
For a better understanding of the conventional converter system, it will be 
more particularly explained: 
Normally, the tolerance in centering lens axes between the converter and 
the master lens is .+-.0.02 mm at maximum, and a permissible eccentricity 
is about 2' in which no appreciable degree of adverse effect will result. 
Now, let us suppose that an 8 mm motion-picture camera has a master lens 
having a focal length (f.sub.M) of 25.0 mm; then the permissible 
eccentricity of the rear member, in terms of focal length, will be: 
##EQU1## 
In the case of a cinemascope, the magnifying power of the converter 
(.beta.) may be 0.5; then the focal length of the front member (f.sub.A) 
will be: 
##EQU2## 
FIG. 1 shows the conventional arrangement of lenses on the actual scale, in 
which the front member 1', the rear member 2', the master lens 3' and a 
film 4 are respectively arranged. As evident from the drawing, the rear 
member 2' has a relatively large effective diameter compared with that of 
the master lens 3', and the distance therebetween is also 
disadvantageously large. 
When forming wide-ranging images on a wide screen, the optical instrument 
requires the provision of cylindrical lenses capable of directional 
widening, and in order to achieve it, all the lenses must be properly 
centered, that is, the center of curvature of all the lens surfaces should 
line on the lens axis, so as to constitute a unitary optical system. 
However, it is difficult to properly combine these lenses in a mount 
especially when they are made of glass. In addition, when such a complete 
set of lenses including cylindrical lenses is attached to the main optical 
instrument with the use of screws or any other fastening means in the same 
manner as when a convertible lens or any other attachment is mounted, it 
may happen that wide-ranging images are projected on the wide screen in 
their tilting posture although the lenses are properly centered. 
DISCLOSURE OF THE INVENTION 
A feature of the present invention lies in that: 
When the focal lengths of the front member and the rear member of the 
converter, and of the master lens are f.sub.A, f.sub.B and f.sub.M, 
respectively, a relationship among them can be established: 
EQU 4f.sub.M .gtoreq..vertline.f.sub.B .vertline..gtoreq.2f.sub.M ( 1) 
and that the focal length (f.sub.B) of the rear member is determined such 
that the above Formula (1) is satisfied. As a result, the diameter of the 
rear member is reduced substantially to that of the master lens, and 
additionally, the diameter of the front member and the length of the 
cylindrical mount are considerably reduced compared with those under the 
conventional converter system. From Formula (1), it will be understood 
that if f.sub.B is larger than 4f.sub.M, the converter as a whole will be 
increased in size, and that if f.sub.B is smaller than 2f.sub.M, the 
difficulty of compensating aberration results, and additionally, the 
arrangement of lenses become complicated. 
Another feature of the present invention is that the front member and the 
rear member consisting of cylindrical lenses are all made of optical 
plastics, thereby securing a light weight, easy assembling and 
trouble-free adjustment of the lens axis. This leans to a reduced 
production cost. More concretely, the front member and the rear member are 
provided with tiny tenons at their rim portion, and the mount includes 
recesses adapted to receive the tenons, so as to combine the lenses in a 
correct relationship with no special care in adjustment. This also 
eliminates the necessity for a supplemental inspection instrument and a 
lens fixing apparatus.

DESCRIPTION OF A PREFERRED EMBODIMENT 
By taking an example for an 8 mm motion-picture camera, a preferred 
embodiment will be described: 
Likewise, let us suppose that the focal length of the master lens (f.sub.M) 
is 25.0 mm, and that the focal length of the rear member of the converter, 
i.e. f.sub.B is equal to the upper limit in Formula (1), that is: 
EQU f.sub.B =4f.sub.M =100.0 mm 
Table 1 numerically shows the mode of lens arrangement in this embodiment. 
In Table 1, R(mm) is the curvature of lens surface, D(mm) is the distance 
from a first lens surface to the neibouring second lens surface, N is the 
refractive index of an object in front of the first lens surface, .gamma. 
is the gamma value of the object, and .phi. (mm) is the effective diameter 
of the lens. The cardinal number 1, 2, 3 . . . shows the lens number, 
which is appended to each lens. 
From Table 1, it will be understood that the effective diameter of the 
front member of the converter, i.e. .phi..sub.1 is 28.0 mm and that the 
total length of the converter 
##EQU3## 
FIG. 2 shows the arrangement made on the basis of the data in Table 1, in 
which the front member 1 and the rear member 2 consist of cylindrical 
lenses while the master lens 3 consists of an ordinary non-directional 
type of lenses. Reference numeral 4 denotes a film. 
In FIG. 3, a more concrete arrangement of the lenses is shown. The front 
member 1 includes lenses G.sub.1 and G.sub.2, and the rear member 2 
includes lenses G.sub.3 and G.sub.4. The master lens 3 includes lenses 
G.sub.5, G.sub.6, G.sub.7 and G.sub.8. 
The lenses G.sub.1, G.sub.2, G.sub.3 and G.sub.4 are made of optical 
plastics, each consisting of a lens portion and a rim portion produced in 
one body. The lens G.sub.1 is provided with a pair of recesses 8, each 
being located at diametrically opposite side of the rim. Reference numeral 
5 denotes the inner end face of the lens G.sub.1 adapted to meet the outer 
end face 6 of the lens G.sub.2 in which tenons 9 are provided so as to fit 
in the recesses 8. The inner end face 7 of the lens G.sub.2 includes a 
pair of tenons 10, each being located at diametrically opposite side of 
its rim. Likewise, the lens G.sub.3 of the rear member is provided with a 
pair of tenons 14, each being located at diametrically opposite side of 
its rim, in which reference numeral 11 denotes the outer end surface of 
the lens G.sub.3. The lens G.sub.3 includes a pair of recesses 15 in its 
inner end surface 12, so as to receive tenons 16 provided in the outer end 
face 13 of the lens G.sub.4. These tenons and recesses are produced 
axially with the common lens axis in the peripheral surface of the rims of 
each lens. In producing the tenons and recesses, it must be noted that no 
projection is permitted on the peripheral rim surface. 
In connecting the front member 1 to the rear member 2, a cylindrical 
coupler or mount 17 is employed, consisting of dividable two parts 
17.sub.A and 17.sub.B. The rear part 17.sub.B is rotatably inserted in the 
front part 17.sub.A, and can be secured thereto by means of set screws 19, 
wherein the rear part 17.sub.B is stopped from its further insertion by a 
ring-shaped flange 18 produced on the inside wall of the front part 
17.sub.A. When the set screws 19 are unfastened, the front part 17.sub.A 
can also be rotated with respect to the rear part 17.sub.B. The front part 
17.sub.A is provided with a pair of recesses 20, each being located at 
diametrically opposite side of the rim, which recesses are adapted to 
receive the tenons 10 of the lens G.sub.2. Likewise, the rear part 
17.sub.B is provided with a pair of recesses 21, so as to receive the 
tenons 14 of the lens G.sub.3. Preferably, the front part 17.sub.A and the 
rear part 17.sub.B are fastened to each other by means of the set screw 
19 such that the recesses 20 and 21 position on the same plane passing 
through the lens axis. 
When the lenses G.sub.1 to G.sub.4 are to be combined on the coupler 17, 
they are connected from one to another by fitting one tenon in the recess 
of the neiboring component. In this way the assembling is readily finished 
with no use of any special skill and experience. When the lens is found to 
be improperly mounted, it can be easily corrected by loosening the set 
screw 19, thereby facilitating precise setting of the lenses. FIG. 2 shows 
that the lenses are properly combined, in which the coupler 17 is omitted 
for simplicity. 
The coupler 17 is covered with a cylindrical casing composed of dividable 
first part 28 and second part 29 jointed to each other by means of threads 
30. The first part 28 covers the lenses G.sub.1 and G.sub.2, a protector 
glass plate 24 fitted in front of the lens G.sub.1, and the front part 
17.sub.A of the coupler. The second part 29 covers the lenses G.sub.3 and 
G.sub.4, the lenses G.sub.5 to G.sub.6 of the master lens, and the rear 
part 17.sub.B of the coupler. The second part 28 includes a shoulder 
portion 32 adapted to face a main optical instrument 27. The first part 28 
is provided with a ring-shaped rubber band 31; prefereably, the rubber 
band has a dented surface as shown in FIG. 3, so as to impart friction to 
an operator's hand. 
The second part 29 of the casing extends beyond the shoulder portion 32 
(hereinafter referred to as the rearward portion). This rearward portion 
is provided with two ring-shaped bands of soft material, such as blanket 
material, flocked cloth, non-woven cloth, and is rotatably supported in a 
sleeve 26, which is secured to the main optical instrument 27 in a known 
suitable manner. The sleeve 26 is provided with a retractible screw 34, 
and the rearward portion is provided with ring-shaped groove 33 adapted to 
receive the screw 34 therein. Owing to the interposition of the bands 25, 
a ring-shaped space is slightly produced between the rearward portion and 
the sleeve 26, thereby reducing friction likely to occur during the 
rotation of the rearward portion in the sleeve. In addition, the rearward 
portion is precisely rotated about its own axis under the guidance by the 
screw 34 fitting in the ring-shaped groove 33, thereby allowing of no 
deviation thereof in the axial direction. Thus, a distance between the 
lenses and the film 4 is maintained in its proper state. 
APPLICATIONS OF THE INVENTION 
The lens attachment according to the present invention is used as a 
convertible lens for a photograph camera, a motion-picture camera, and an 
enlarger, and also it is used as a supplemental lens unit for attachment 
to the main master lens. 
TABLE 1 
__________________________________________________________________________ 
Type of Refractive Effective 
Lenses 
Lens No. 
Curvature mm 
Distance mm 
Index .nu. value 
Diameter mm 
__________________________________________________________________________ 
Front 
G.sub.1 
R.sub.1 = 159.35 
D.sub.1 = 6.0 
N.sub.1 = 1.0 
.nu..sub.1 = 1.0 
.phi..sub.1 = 28.0 
Member R.sub.2 = -159.35 
D.sub.2 = 0.2 
N.sub.2 = 1.58600 
.nu..sub.2 = 34.8 
.phi..sub.2 = 28.0 
G.sub.2 
R.sub.3 = .infin. 
D.sub.3 = 3.3 
N.sub.3 = 1.0 
.nu..sub.3 = 1.0 
.phi..sub.3 = 28.0 
R.sub.4 = 18.56 
D.sub.4 = 37.64 
N.sub.4 = 1.49200 
.nu..sub.4 = 57.8 
.phi..sub.4 = 28.0 
Rear G.sub.3 
R.sub.5 = .infin. 
D.sub.5 = 3.0 
N.sub.5 = 1.0 
.nu..sub.5 = 1.0 
.phi..sub.5 = 22.0 
Member R.sub.6 = 88.22 
D.sub.6 = 1.1 
N.sub.6 = 1.58600 
.nu..sub.6 = 34.8 
.phi..sub.6 = 18.0 
G.sub.4 
R.sub.7 = -268.26 
D.sub.7 = 5.0 
N.sub.7 = 1.0 
.nu..sub.7 = 1.0 
.phi..sub.7 = 18.0 
R.sub.8 = -27.56 
D.sub.8 = 1.0 
N.sub.8 = 1.49200 
.nu..sub.8 = 57.8 
.phi..sub.8 = 18.0 
Master 
G.sub.5 
R.sub.9 = 33.2 
D.sub.9 = 2.9 
N.sub.9 = 1.0 
.nu..sub.9 = 1.0 
.phi..sub.9 = 17.8 
Lens R.sub.10 = 904.6 
D.sub.10 = 0.2 
N.sub.10 = 1.62041 
.nu..sub.10 = 29.5 
.phi..sub.10 = 18.0 
G.sub.6 
R.sub.11 = 16.7 
D.sub.11 = 6.9 
N.sub.11 = 1.0 
.nu..sub.11 = 1.0 
.phi..sub.11 = 17.0 
R.sub.12 = 81.8 
D.sub.12 = 0.8 
N.sub.12 = 1.65160 
.nu..sub.12 = 58.5 
.phi..sub.12 = 14.0 
G.sub.7 
R.sub.13 = -132.75 
D.sub.13 = 7.0 
N.sub.13 = 1.0 
.nu..sub.13 = 1.0 
.phi..sub.13 = 14.0 
R.sub.14 = 9.1 
D.sub.14 = 3.1 
N.sub.14 = 1.72825 
.nu..sub.14 = 28.3 
.phi..sub.14 = 9.0 
G.sub.8 
R.sub.15 = 16.2 
D.sub.15 = 6.4 
N.sub.15 = 1. 
.nu..sub.15 = 1.0 
.phi..sub.15 = 10.5 
R.sub.16 = -21.1 
N.sub.16 = 1.71300 
.nu..sub.16 = 53.9 
.phi..sub.16 = 10.5 
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