JPH01142518A - Double focus switching lens system - Google Patents

Abstract

PURPOSE:To improve the fluctuation in lens back by a temp. change and to prevent an increase of cost by providing at least a piece of plastic lens having a positive refracting power as a main lens and providing at least a piece of plastic lens having a negative refracting power as a rear converter lens. CONSTITUTION:The main lens I is so constituted as to have at least a piece of the plastic lens having the positive refracting power and the rear converter lens II is so constituted as to have at least a piece of the plastic lens having the negative refracting power. The quantity of the fluctuation in the lens back of the main lens by the temp. change and the quantity of extension of the body by the temp. change are canceled by the quantity of the fluctuation generated in the rear converter lens II. The increase in the cost of a camera is thereby not resulted even if the quantity of the fluctuation in the lens back by the temp. change is decreased.

Description

[Detailed description of the invention] The present invention relates to a bifocal switching lens system.

Conventionally, in order to reduce costs, it has been considered to use plastic lenses in lens systems, which are lightweight, but
When a plastic lens is used, the lens pack fluctuates greatly due to changes in temperature, resulting in large fluctuations in the image point.This situation also applies to the bifocal switching lens system according to the present invention. In this type of lens system,
In particular, this fluctuation becomes thicker when a rear converter lens is inserted.

In a bifocal switching lens system, if a plastic lens is used only for the main lens, no plastic lens is used for the rear converter lens, and lens back fluctuations caused by the plastic lens that occur in the main lens due to temperature changes are not corrected, the long focal length The state, that is, the fluctuation of lens back when both the main lens and rear converter lens are on the optical axis is as follows.

ΔLBT=ΔLBXff” −・−・(A) However, here, ΔLBT is the amount of lens pack fluctuation of the entire system in the long focus state, ΔLB is the amount of lens pack fluctuation of only the main lens, and the expansion of the a beam 7 converter lens. In other words, in the short focal length and α state, the amount of lens back variation (ΔL
Even if B) is within the allowable range, the lens pack fluctuation amount (ΔLBT) in the long focus state may exceed this allowable range. This becomes more difficult when the magnification is high.

Furthermore, in the long focal state, in addition to the manufacturing error of the main lens, the manufacturing error of the rear converter lens, the positional error between the main lens and the I77 converter lens, etc. are added to the total error. Lens pack variation amount (
ΔL 8T) becomes increasingly severe.

In addition, in order to solve lens back fluctuations due to temperature in a bifocal, αgJIF lens system, it is necessary to limit lens back fluctuations due to temperature changes in the main lens to approximately θ, and also to approximately zero in the rear converter lens.
However, reducing the amount of lens pack fluctuation due to temperature changes in each case would increase the number of lenses and complicate the configuration.Also, it would be necessary to compensate for lens back fluctuations due to temperature changes on the body side. Although it is possible to do so, this also increases the cost of the camera.

The present invention has been made in view of the above problems, and it is an object of the present invention to provide a bifocal switching lens system that satisfactorily solves lens back fluctuations due to temperature changes and does not increase costs.

The present invention will be explained in more detail below.

As is clear from FIG. 3.7.11 showing the long focal state of each embodiment, the bifocal switching lens system according to the present invention has a main lens (I) with positive refractive power and an optical axis behind it. In a bifocal switching lens system that has a negative refractive power Nori-Afunpater lens (n) that changes the focal length of the entire lens system by moving it in and out of the top, the main lens (1,) has a small The rear converter lens (n) is characterized by having a plastic lens having a refractive power and at least one plastic lens having a negative refractive power.

In the present invention, a plastic lens is used in the rear converter lens (II) in addition to the main lens (1),
The main lens (1) is configured to generate a lens pack variation amount of the opposite sign (direction) to the lens pack variation amount (ΔLB) due to the temperature change in the rear converter lens (II). The amount of lens pack variation (ΔLB) of the lens or, in addition, the amount of body expansion due to temperature changes can be calculated using this rear converter lens (
This is canceled by the amount of lens pack fluctuation that occurs in II).

Furthermore, in the present invention, the refractive power of the plastic lens used for the main lens (1) is positive and the rear converter 1/lens (
A configuration is adopted in which the refractive power of the plastic lens used in II) is negative. Here, for comparison, starting from the object side,
A first lens is a plus lens with positive refractive power, a second lens is a glass lens with negative refractive power, a third lens is a glass lens with positive refractive power, and a plastic lens has positive refractive power. A rear converter lens (II) consisting of a main lens (1) consisting of a certain fourth lens, a tJII5 lens which is a glass lens having positive refractive power, and a sixth lens which is a plastic lens having negative refractive power. Consider a bifocal switching lens system having the following.

In Japanese Patent Application No. 61-311448, the present applicant proposed that the composite refractive power of the plastic lens in the rear wing converter lens (■) be positive.

This is because when the magnification in the long focal length state is large, that is, when the focal length of the rear converter lens is short, if the composite refractive power of the plastic is negative, the rear This is because the Petzval sum of the converter lens becomes negative and the curvature of field becomes large in the long focal state. When the focal length is relatively long, even if the composite refractive power of the plastic lens in the rear converter lens is negative, the curvature of field in the long focus state can be kept small. Consists of force in the negative.

On the other hand, in order to reduce the amount of image point movement due to temperature changes, it is desirable to do the following.

The amount of image point movement (L) due to temperature change is given by David
S.

A Lherwalization by Gray
of Optial Systems (JO8A
, 1948), where: N: number of lenses in the lens system, fi: focal length of the i-th lens, hi: height of incidence of paraxial rays on each lens, nl(T ,
), nl(T), nl(T2): refractive power at each temperature (T, <T<T□), and the smaller the value of L, the smaller the amount of image movement due to temperature change. Become.

In the lens system mentioned above as an example, the image point movement amounts (L) in the long focus state and the short focus state are as follows.

f4II+4 r　a　　w4　　　　f5　wgHowever, here, LH: Image due to temperature change in short focus state, amount of air movement, LT: amount of image point movement due to temperature change in long focus state, It is.

Here, the third lens, the second lens, the third lens, and the fifth lens
The lens is a glass lens, and each temperature dispersion number (w +
) is larger than the 4.6th lens made of plastic and can be ignored. At this time, the second term in the above equation (C) is the value of the sixth lens made of a negative plastic lens, which is a negative value, so in order to reduce LT in the equation (C), (
The value of LM in equation B) must be positive. In this case, the value of LH in the short focus state must be below a certain reference amount, and the value of LH and (
C) By balancing the value of the second term of the equation and making the value of LT below a certain reference value, the amount of movement of the image point due to temperature change can be kept within a practically acceptable range.

Furthermore, in the present invention, it is desirable that the following conditions be satisfied at a predetermined reference temperature.

(1) 0.3<φb/φR<7.0(2)
0.1<φa/φM<2.0 However, here, φa: Composite refractive power of the plastic lens in the main lens, φM: Composite refractive power of the main lens, φb: Composite refraction of the plastic lens in the rear converter lens power, φR: composite refractive power of the rear converter lens.

As mentioned above, when the magnification of the rear converter lens is relatively small, that is, when the combined focal length of the 7 converters is large, the negative plastic lens installed in the rear converter lens whose refractive power of the entire system is negative. By keeping the combined refractive power within a certain range, the Petzval sum, which tends to take a large value in the negative direction, can be kept relatively small.

Condition (1) is for this purpose. 0 If the lower limit of condition (1) is exceeded, the second term in the above equation (C) becomes too small and has the opposite sign that cancels out the amount of image point movement due to temperature change of the main lens. The amount of movement of the image point becomes insufficient, and the Petzval sum tends to take a large value in the negative direction.

On the other hand, if the upper limit of condition (1) is exceeded, the amount of image point movement with the opposite sign becomes too large.

Condition (2) is a condition for determining the refractive power of the plastic lens in the main lens under condition (1). conditions(
If the lower limit of 2) is exceeded, the amount of movement of the image point of the main lens due to the temperature of the entire system can be reduced, but when the condition (
Under 1), the amount of lens back fluctuation of the rear converter lens in the negative direction becomes too large. Conversely, if the condition (
If the upper limit of 2) is exceeded, the amount of movement of the image point due to temperature changes in the main lens, that is, in the short focus state, will become unacceptably large.

Hereinafter, examples of the present invention will be shown, and the numerical values in the examples are 20℃
* L + t L 21 L s =
・is the lens counted from the object side, rllr2tr3...
is the radius of curvature of the surface counted from the object side, d, , d, , d,
... is the axial distance counted from the object side, n1yl12wn
i... is the refractive index of the lens counted from the object side, shi, shi2
．． ν, . . . indicate Atsube's number.

The surface marked with "East" indicates that it is an aspheric surface, and its shape is expressed by the X coordinate in the optical axis direction, and .

If the Y coordinate is taken in the vertical direction and the paraxial curvature is ri, then @
It is expressed as CY'+DY'+EY16+FY12. However, A, B, C, D, E, F... are aspheric coefficients.

f represents the focal length, and 2ω represents the angle of view.

(Margin below) Table 1 (Example 1) Main lens f = 34.9 FNO = 3.59 2ω = 63.6° Radius of curvature Core thickness Refractive index (Nd) Atsbe number (
I'd)φ1/φ, ='0.7 Table 2 (Example 1) Composite lens system of main lens and rear converter lens f=
43.75 FNO=4.50 2ω=52,6
° Radius of curvature Core thickness Refractive index (Nd) Atsube number (νd) φb/φR = 4.23 Table 3 (Example 2) Main lens f = 35. OFNO=2.90 2ω=63.4°Curvature radius Core thickness Refractive index (Nd) Atsube number (Md) A=0,0 B=0.44114X10-'C=-0.42658X10-' D=0. 17518X10-1 E=0. 83532X10-'F=-0.13894xlO・φa/φ,=0.75 Table 4 (Example 2) Composite lens system of main lens and rear converter lens.

f=54. OFNO=4.47 2ω'=43.
7゜A=0.0 B=0.44114X10-'C=-0,42658X10"D=0,17518X10-'E=0.83532X10"F=-0,13894X10" φb/φR=3.03 Fifth Table (Example 3) Main lens f = 38. OFNO = 3,50 2ω = 59.3° Radius of curvature Core thickness Refractive index (Nd) 7-point number (
νd)ry oo (aperture) A=0.0 B=-0,18494X10-'C=-0,90341X10-"D=0.77677X10-1' E=0.85473X10-12 φ, /φ, = 1 .84 Table #6 (Example 3) Composite lens system of main lens and 7 component lenses f = 5
7. OFNO = 5.25 24kl = 41.6゜ Life rate cow diameter rP a m refractive index (Nd) 7 f < number (ld
)^=0.0 B=-0,18494X10°C=-0,90341X10-"D=0.77677X10" E=0.85473X10°l3 -b/φ,=5.88 In all examples Tables 7 and 8 show lens pack fluctuations due to temperature changes of the main lens, main lens, and rear converter lens, respectively.

For example, in the first* example, the fourth lens out of four lenses
The lens is a plastic lens, but if you calculate the amount of change in lens back at 50 degrees Celsius based on the lens pack at 20 degrees Celsius, it will be +0.138 m5, and the amount of change at -10 degrees Celsius is -0,
It is 138m5. In addition, the sixth lens in the rear converter lens consisting of the fifth lens and the sixth lens is a plastic lens, but the lens pack value when the temperature changes from 50 degrees Celsius to -10 degrees Celsius in the long focus state is 50 degrees Celsius based on 20 degrees Celsius.
Calculating the amount of variation of lens pack in °C is -0,029m
5. The amount of variation at -10℃ is +0.028m-, jI
In the first embodiment, the amount of lens pack fluctuation due to temperature change in the main lens system is allowed. The main lens and rear converter lens are configured to have a smaller amount of fluctuation in the long focal state where they are on the optical axis.

Table 7 Main Lens Table 8 Main Lens + Rear Converter Lens (Unit: 5-
) (margin below)

[Brief explanation of the drawing]

Figure 1111 is a cross-sectional view showing Kiren K of Example 1 of the present invention,
Figure 2 is an aberration diagram of the main lens, Figure 3 is a sectional view showing the entire lens system when a rear converter lens is attached to the main lens of Example 1, and Figure 4 is an aberration diagram of the entire lens system. , FIG. 5 is a sectional view showing the main lens of Example 2 of the present invention, FIG. 6 is an aberration diagram of the main lens, and FIG. A sectional view showing the entire lens system, FIG. 8 is an aberration diagram of the above-mentioned entire lens system, and FIG. 9 is a sectional view showing the main lens of Example 3 of the present invention, $
Figure 10 is an aberration diagram of the main lens, Figure #111 is Example 3.
FIG. 12 is a sectional view showing the entire lens system when a rear converter lens is attached to the main lens of , and FIG. 12 is an aberration diagram of the entire lens system. (1); Main lens, 1■; Rear converter lens. Applicant Mi/Rutaka/F Co., Ltd. Figure 1 r Figure 2 Ball → L! 1. ri r, east, qc L
Running percentage 3rd drawing I Akira 7th ink, soo L main straddle 9th
Figure ■ Figure 10 Construction method ° Visit Mata Arai Jun 1. Kidney 1JL1
1! ] %Figure II Figure 12

Claims (1)

[Claims] 1. A bifocal switching lens system having a main lens with positive refractive power and a rear converter lens with negative refractive power that switches the focal length of the entire lens system by moving it in and out on the optical axis behind the main lens. 2, wherein the main lens has at least one plastic lens with positive refractive power, and the rear converter lens has at least one plastic lens with negative refractive power.
Focus switching lens system. 2. 2 as set forth in claim 1, which satisfies the following conditions at a predetermined reference temperature.
Focus switching lens system: 0.3<φb/φR<7.0 0.1<φa/φM<2.0 However, here, φa: composite refractive power of the plastic lens in the main lens, φM: composite refractive power of the main lens Composite refractive power, φb: Composite refractive power of the plastic lens in the rear converter lens, φR: Composite refractive power of the rear converter lens.