JPH02134611A - Symmetrical wide-angle lens system for copying - Google Patents

Abstract

PURPOSE:To reduce the size of a copying machine main body by forming at least two symmetrical surfaces of a 1st negative lens and an 8th lens in an aspherical surface shape of rotational symmetry. CONSTITUTION:A lens system of eight-group, eight-element consists of a 1st negative lens, a 2nd positive lens, a 3rd negative lens, a 4th positive lens, a stop, and a 5th positive lens, a 6th negative lens, a 7th lens, and an 8th negative lens which are symmetrical about the stop. Then, at least two symmetrical surfaces of the 1st negative lens and 8th lens are in aspherical surface shapes of rotational symmetry. Namely, the 1st negative lens and 8th negative lens which are at long distances from the stop and large in shift in the passing position of an off-axis main light beam due to a view angle are made aspherical, and the off-axis aberration, specially, astigmatism and distortion of field are easily compensated. Consequently, a superwide view angle is obtained and the whole device is reduced in size.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a full exposure type copying lens system that allows a projection lens system to have a wide angle of view, thereby reducing the size of the entire apparatus.

[Prior Art] The exposure methods of commonly used copying machines are broadly classified into slit scanning type and full exposure type. In the former case, the angle of view of the slit with respect to the scanning direction is small, and the bending by the scanning mirror can be performed using a long mirror, so the design is easy. Therefore, there is an advantage that the common distance from the original surface to the exposure surface of the photoreceptor can be made relatively large, and the projection lens system does not need to have an extremely wide angle of view.

On the other hand, a drawback of the slit scanning type is that since it includes a scanning section, there is a limit to the copying speed.

The latter full-surface exposure type does not have a complicated scanning movement mechanism, so it has the advantage of being able to copy at a much faster copying speed than the former. However, since this results in an increase in the size of the entire system and an increase in cost, a method of direct projection without using a folding mirror or the like has been adopted.

[Problems to be Solved by the Invention] In the above-mentioned full-surface exposure type copying apparatus, the overall size of the copying apparatus is limited to the document l on the document table 2 and the belt photoreceptor 3, as shown in FIG. Common distance between upper exposure surface 1ll
It will be greatly influenced by L. Note that the reference numeral 4 is a projection lens system.

In order to downsize the main body of the copying machine, it is necessary to
In practice, it is necessary to make L small and the projection angle of view to be 2ω=60” or larger.

This invention was made in view of the above points, and has a projection angle of view of 2ω = 86°, which is an ultra-wide angle of view, and F = 1.
The purpose of the present invention is to provide a lens system for projection that is as bright as 0.

[Means for Solving the Problems] The present invention includes a first lens having a negative side from the object side, a second positive meniscus lens having a convex surface facing the object side, and a third lens having a negative meniscus having a convex surface facing the object side. , a positive meniscus fourth lens with a convex surface facing the object side, an aperture, a fifth lens arranged symmetrically with the fourth lens with respect to the aperture, and a sixth lens also arranged symmetrically with the third lens. , a seventh lens also arranged symmetrically with the second lens, and an eighth lens also arranged symmetrically with the first lens, the first lens of the negative lens and the eighth lens.
This is a symmetrical French angle of view lens system for copying, in which at least two symmetrical surfaces of the lens have a rotationally symmetrical aspherical shape.

[Example] First, the effect when a negative lens is placed on the magnification side will be explained with reference to the drawings. The paraxial arrangement of the entire system is symmetrical with respect to the aperture S, as shown in FIG. If the maximum object length is y (y<O), and the distance from the front principal plane H to the object surface 1 is a (a<O), then the converted inclination α of the principal ray at the maximum angle of view that enters the lens is. becomes α0 =−(α.<0).

The first negative lens of this invention is the A group, and the second positive lens is t
If the JS3 negative lens and the fourth positive lens are collectively considered to be group B, it can be considered as a lens system consisting of four groups, negative, positive, positive, and negative, symmetrical about the aperture S, as shown in FIG.

The refractive power of the A group (reciprocal of the focal length) is φ, and the refractive power of the B group is φ6. When the thin-wall equivalent surface spacing between groups A and B is e, and paraxial tracking is performed using the principal ray at the maximum angle of view as the incident ray, the converted inclination angle α1 of the ray incident on group B is the height of incidence on group A. as 1.

α,=α0−φ8<0, and since φ,〈0, α,−α. = -φ〈0, the feed value of the converted inclination angle incident on the B group becomes small, and for a symmetric lens group including the B' group, which is arranged symmetrically with respect to the aperture S of the B group, a small image This means that it can be designed with corners.

From another perspective, the object point for group B and the image point for group B' will move away from each other, and the same object length y
This means that the joint yoke length can be virtually increased,
Very advantageous conditions can be created for correcting aberrations.

As shown in FIG. 1, the projection lens system of the present invention includes, in order from the object side, a first negative lens, a second positive lens, a third negative lens, a fourth positive lens, an aperture, and the following are symmetrical with respect to the aperture. Fifth
Positive lens, 6th negative lens.

This is a lens system with eight lenses in eight groups, including a seventh positive lens and an eighth negative lens.

At least two symmetrical surfaces of the first negative lens and the eighth negative lens have rotationally symmetrical aspherical shapes.

Furthermore, the aspherical shape has a shape in which the refractive power increases in the negative direction as the distance from the optical axis increases compared to the reference curvature. Group B and group B' are modified types of orthometa-type.

Furthermore, in order to accommodate a wide angle of view, the first lens and the eighth lens are configured as negative lenses, as described above, and the B
The lens is configured to reduce the angle of view for the groups B and B'.

When the projection lens system of the present invention has an ultra-wide angle of view of 2ω=85' and is compact, the biggest problem is an increase in off-axis astigmatism.

In this invention, the first negative lens and the eighth negative lens, which are located at the farthest position from the aperture S and whose passing position of the off-axis principal ray changes greatly depending on the angle of view, are aspherical, thereby eliminating off-axis aberrations. In particular, it facilitates correction of astigmatism and field curvature.

In particular, as the direction of divination of the aspheric surface, it is effective to have a shape in which the refractive power increases in the negative direction as the distance from the optical axis increases compared to the reference spherical surface.

This corresponds to the direction of reducing the Petzval sum that defines the astigmatism difference, and effectively corrects the image surface property.

Also, the radius of curvature r of the surface of the second lens on the aperture S side, and the third
The lens is configured so that the radius of curvature r5 on the object side satisfies the following conditional expression.

r, > rs... (1) As a result, since it has a relatively wide angle for the B and B' groups, it takes a concentric shape with respect to the aperture S, and by setting r4 > rs. This makes it easy to correct off-axis aberrations.

Furthermore, in this invention, the focal length of the first negative lens is f+
+When the focal length of the entire system is f, -2,5f<f,<-
1.0f...Is it necessary to satisfy the condition (2)?

This conditional expression is a condition for reducing the angle of view of the incident light rays to the B group and B' group, and also for making the total lens length Σd compact. If the lower limit is exceeded, α, and α. The difference between
It becomes difficult to correct off-axis aberrations. If the upper limit is exceeded, the negative refractive power of the negative lens group will be too large, and the overall length of the lens will become large, as seen in, for example, US Pat. No. 3,567,310.

Furthermore, in this invention, by using synthetic resin lenses as the first lens and the eighth lens, which have aspherical surfaces with the largest outer diameters, mass production is possible through molding, which can significantly reduce costs. .

Examples 1 to 6 of specific symmetrical wide-angle lens systems for copying that satisfy these conditional expressions are shown in Tables 1, 3, and 5 below.
Table 7, Table 9, and Table 11 show the corresponding lens system configurations in Figures 1, 3, 5, 7, 9, and 11. . In addition, the respective aberration curve diagrams are shown in Fig. 2, Fig. 4, Fig. 6, Fig. 8, and Fig. 10.
and FIG. 12. Table 6 shows numerical values for each surface of the lens' radius of curvature, axial spacing, refractive index at the d-line, and number of radials.

Furthermore, Table 2 shows the aspheric coefficients of Examples 1 to 6.

The results are shown in Table 4, Table 8, Table 1O, and Table 12, respectively.

The aspherical coefficient A in these six tables is taken as the optical axis, the X-axis, and the orthogonal coordinate y-axis in the plane of x=0.

When taking the Z axis, the aspheric surface is expressed as x=f (y, z), and the value of Ai is given by setting y2+z2=Φ2. However, co is the reciprocal of the radius of curvature.

The first to third examples are examples in which the first lens and the eighth lens are made of glass, and the fourth example to the sixth example are examples in which the first lens and the eighth lens are made of synthetic resin. It is.

(Left below) Table I f=140. IFNO,=IO,0 Radius of curvature Distance between upper surfaces of shaft Refractive index (Nd)rr” −:
153.627 d, 2.260 N, 1.59551r2ff
i 267.305 d21.30? r3:10.696 d37.300 N21.7650Or<57
．． 411 d41.963 rs 39.567 d52.404 N31.68300re 2:
1.036 da 2.767 r, 60.748 d, 3.426 N, 1.7170nra 1
28.142 +1. 5.241 d95.241 rq -128,142 Atsube number (υd) 39.23 υ246.25 υ, 31.52 υ447.86 d,, 2.767 r,, -23,035 d, 22.404 rr2- 39.567 dl:+ 1.96:1 rrx -57,411 d, 47. :100 rr4-:IO,696 d, 51.307 r,,"-267,305 d1=, 2.26O r,," :153.627 N61.68ko0ON, 1.7650ON, 1.59551 υ631.52 v, 46.25 υ, 39.23 f-140,1 th FNO,= 9.0 268.643 30.670 5? , 481 39.596 23.839 60.356 2.337 1.402 7.166 1.960 2.325 2.914 1.59551 N21.7650O N, 1.68:10:19.2:1 υ246 .25 υ3:11.52 r9 -129.525 r8゜ -60,356 rrs -23,039 r,! -39,596 rll -57,481 rr< -30,670 r, "-268,64:1 rrs" 328.140 do 4.910 d, 4.910 dlo 3.476 dt+ 2.914 d,, 2 .325 dl:l 1.960 d,, 7.166 d,, 1.402 dla 2. :137 N51.7170O N6 1.6830O N, 1.7650O N, 1.59551 υ, 47.86 υ, 31.52 υ746.25 V839.23 Σd=52.979 Fifth Table f=140. I FNO, = 8.0 Radius of curvature Distance between upper surfaces of axis Refractive index (Nd) r, W -2
89,649 dl 2.328 N, 1.59551r, 11
269.528 d21.394 r+ 30.647 d, 7.084 N, 1.7650Or,
57.742 d, 1.996 r539.502 ds 2.131 N11.68300rG23.
066 d63.101 rt 59.905 d, 4.336 N, 1.7170Or6 13
1.097 d84.207 dq 4.207 r9 -131.097 t+o 4.336 N51.7170 mouth ",
. -59,905 d1□3.101 r,, -23,066 d,□2.131 N61.68300r, 2-39
．． 502 d,, 1.996 r, 3 -57.742 dI47.084 N? 1.76500r, 4-3
0.647 d, 51.394 r+s"-269,528 dla 2.328 No 1.59551rll+
” 289.649 Σd−53,153 Avbe number (υd) 39.23 υ246.25 υ, 31.52 υ, 47.86 υ, 47.86 υ631.52 υ, 46.25 υ, 39.23 rx" 267J40 d21.307 d41.963 "6 2ko, 036 rt 60.747 ra 121i, 835 2.767 3.426 5.241 5.241 1.720 Roro υ, 54.71 r+o -60,747 d ,, 2.767 r,, -39,566 r+3 -57.413 r+< -30J95 r15ζ267, 34O r,," 353. ．． 633 d, 31.963 a,, 7.300 d, 51.307 dla 2.260 Σd= N71.7620O N, 1.58400 53, :137 υ? 40.36 υ83t, o.

f-140,1 9th FNO,=IO,0 295,7:14 30.758 55.308 :19.296 23.329 66.366 146.950 jg -146,950 rlo -66,366 r,, -23,329 rr2-39.296 r, 3-55.308 r+4-:IO,758 r,,"-295,734 d, 0.600 d, 7.338 d, 1300 ds 2.456 d62.765 d, 3.426 d85.268 d95.268 d,, 3.426 dl, 2.765 dl22.456 dl31.300 d,, 7.338 d1% 0.60 mouth N2 1.76200 1.68:10 mouth N, 1.7200O N5 1.7200O N, 1.6830O N, 1.76200 υ240.36 υ331.52 υ, 54.71 υe, 54.71 υ631.52 υ, 40.36 Σd= 51.306 "3 :IO,741 d21゜285 39.344 (L 2.213 61.378 da 3.248 r, -128,474 d, 3.902 r,, -2:1.101 d,, 3.248 r13 - 58.754 rls"-, 261,032 Σd= 54.642 [Effects of the Invention] As explained above, the symmetric wide-angle lens system for copying of the present invention has an ultra-wide angle of view of 2ω = 86 degrees. , it is possible to miniaturize the entire device by using it in a full exposure type copying device.In addition, although it is an ultra-wide angle (lens total length) /
The lens system has a compact (focal pressure ft of the entire system) of about 0.38, and has extremely good projection performance over the entire screen as shown in each aberration curve diagram.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing the lens configuration of Example 1 of the present invention. FIG. 2 is an aberration curve diagram of the lens system shown in FIG. 1 above. Figure $3 is a cross-sectional view showing the lens configuration of Example 2 of the present invention. Fig. 4 is an aberration curve diagram of the lens system shown in Fig. 3 above, Fig. 5 is a sectional view showing the lens configuration of Example 3 of the present invention, and Fig. 6 is shown in Fig. 5 above. An aberration curve diagram of the lens system. Figure f:fS7 is a sectional view showing the configuration of the lens a of Example 4 of the present invention. Figure 8 is an aberration curve diagram of the lens system shown in Figure 7 above. The figure is a sectional view showing the lens configuration of Example 5 of the present invention, Figure 1O is an aberration curve diagram of the lens system shown in Figure 9 above, and Figure 11 is the lens of Example 6 of the present invention. 12 is an aberration curve diagram of the lens system shown in FIG. 11, FIG. 13 is a schematic diagram showing the exposure system of a copying apparatus which is the background of the present invention. FIG. 14 is a paraxial layout diagram for explaining the present invention in detail. FIG. 15 is a paraxial arrangement diagram for explaining the passage of off-axis extra-generated rays when the entire system is configured with four groups.

Claims (1)

[Claims] 1. A first lens with a negative side toward the object side, a second lens with a positive meniscus with a convex surface facing the object side, a third lens with a negative meniscus with a convex surface facing the object side, and a third lens with a negative meniscus with a convex surface facing the object side. A fourth lens with a positive meniscus directed toward the diaphragm, a fifth lens arranged symmetrically with the fourth lens with respect to the diaphragm, also the third lens
A sixth lens arranged symmetrically with the lens, a seventh lens also arranged symmetrically with the second lens, and an eighth lens also arranged symmetrically with the first lens, the negative lens A symmetrical wide-angle lens system for copying, characterized in that at least two symmetrical surfaces of the first lens and the eighth lens have a rotationally symmetrical aspherical shape. 2. The symmetrical wide-angle lens system for copying according to claim 1, wherein the aspherical surface has a shape in which the refractive power increases in a negative direction as the distance from the optical axis increases compared to a reference curvature. 3. The radius of curvature r_4 of the aperture side surface of the second lens and the third
The radius of curvature r_5 on the object side of the lens is r_4>r_5・
(1) The symmetrical wide-angle lens system for copying according to claim 1, which satisfies the conditional expression. 4. Claim 1 which satisfies the conditional expression -2.5f<f_I <-1.0f (2), where the focal length of the first lens is f_I and the focal length of the entire system is f. The described symmetrical wide-angle lens system for copying. 5. The symmetrical wide-angle lens system for copying according to claim 1, wherein the first lens and the eighth lens are made of synthetic resin.