JPH0353733B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electron gun suitable for application to a cathode ray tube such as a monochromatic or color television picture tube.

A typical color television picture tube is equipped with single-beam type electron guns for each of red, green, and blue. Typical configurations of the main electron lens in these electron guns include a bipotential lens, a unipotential lens, and a tripotential lens.

FIG. 1 shows the electrode configuration of a single-beam electron gun using a bipotential main electron lens system. In this case, on the axis O, there are a cathode K, a first grid G ₁ , a second grid G ₂ , Third Grid G ₃ ,
and a fourth grid _G4 are arranged in sequence. The fourth grid _G4 is supplied with a high anode voltage V _A , and the third grid _G3 is supplied with this anode voltage V _A.
A focus degree V _F of about 20% to 38% is given, and a bipotential main electron lens is constituted by the third grid _G3 and the fourth grid _G4 .

FIG. 2 shows the electrode configuration of a single-beam electron gun using a unipotential main electron lens system. In this case, on the axis O, there are a cathode K, a first grid G ₁ , a second grid G ₂ , Third Grid G ₃ ,
A fourth grid G ₄ and a fifth grid G ₅ are arranged in sequence. 3rd grid G ₃ and 5th grid G ₅
Anode voltage V _A is applied to the fourth grid G ₄ , a focus voltage V _F of about 0% to 40% of the anode voltage V _A is applied to the fourth grid G 4 , and the third to fifth grids G ₃ to G ₅ constitutes a unipotential main electron lens. In this case, the length l of the focus electrode, that is, the fourth grid _G4 , is selected to be 0.2D to 2.5D, where D is the diameter of the fourth grid.

FIG. 3 shows the electrode configuration of a single-beam electron gun using a tripotential main electron lens system. In this case, the cathode K, the first grid G ₁ , the second grid G ₂ , A third grid G ₃ , a fourth grid G ₄ , a fifth grid G ₅ and a sixth grid G ₆ are arranged in sequence. In the 6th grid G ₆ ,
An anode voltage V _A is applied to the fourth grid G ₄ , a focus voltage V F of about 40% of the anode voltage V _A is applied to the fourth grid G 4 , and a focus voltage V _F of about 40% of the anode voltage V A is applied to the fourth grid G ₄ .
G ₅ has an intermediate voltage of about 30% of the anode voltage V _A
V _M is commonly given and the third to fifth grids G ₃
~The first unipotential electron lens was installed in _G5 ,
Further, the fifth and sixth grids _G5 and _G6 constitute a second bipotential type electron lens, and a main electron lens is constituted by combining both lenses.

In addition, in any of the electron guns shown in FIGS. 1 to 3, the second grid G ₂ and the third grid G ₃
A prefocus electron lens is constructed by the following.

However, in the various conventional main electron lens systems described above, aberrations are large, and in particular, when the beam current becomes large, spherical aberration becomes large and the beam spot blooms. This blooming phenomenon significantly deteriorates the reproduced image of the cathode ray tube.

The present invention provides an electron gun, particularly a single beam type electron gun, with small aberrations, especially spherical aberrations, so that such drawbacks can be avoided.

That is, in the present invention, in the single-beam electron gun, the main electron lens system is composed of first and second electron lenses Lens1 and Lens2 whose electron lens action areas are separated from each other. In particular, in the present invention, the first lens system Lens1 has a deceleration type bipotential lens configuration, and the second lens system Lens2 has an extended electric field type acceleration lens configuration. Then, the aperture of the first lens system is made smaller than the aperture of the second lens system.

The electron gun according to the present invention will be explained below.

FIG. 4 shows the arrangement of electrodes in an example of an electron gun according to the present invention.

Also in the present invention, as usual, a cathode and
An electron gun is composed of a prefocus electron lens and a main electron lens, and therefore, as shown in FIG. 4, for example, a cathode K,
A first grid G ₁ and a second grid G ₂ are arranged, and behind these, similarly on the axis O, for example,
The first to fourth electrodes, that is, the third to sixth grids G ₃ ~
Each grid forming the main electron lens consisting of G ₆ is arranged.

In this case, the first electrode (third grid G 3 ) and fourth electrode (sixth grid G ₃ ) constituting the main electron lens
As the applied voltages V ₁ and V ₄ to G ₆ ), the fluorescent surface voltage, that is, the highest voltage anode voltage V _A is given,
The voltage V ₂ applied to the second electrode (fourth grid G ₄ ) is
0.20V _A to 0.40V _A is applied, for example V ₂ =0.3V _A. Further, the voltage V ₃ applied to the third electrode (fifth grid G ₅ ) is set to 0.4V _A to 0.7V _A , for example, V ₃ =0.5V _A.

In this way, the first and second electrodes (third grid G ₃ and fourth grid G ₄ ) of the main electron lens system
The first lens Lens1 is composed of a deceleration type bipotential lens, and the second electrode (fourth grid G ₄ ), the fourth electrode (sixth grid G ₆ ),
Furthermore, by a third electrode (fifth grid G ₅ ) interposed between the two and making the potential gradient between the two gentle,
A second lens Lens2 is constituted by a so-called extended electric field type accelerating lens.

The aperture D ₁ of the first lens Lens1 (i.e. the diameter of each opposing end of the third grid G ₃ and the fourth grid G ₄ ) is:
The aperture D ₂ of the second lens Lens2 is smaller than the diameter of each end of the fifth grid G ₅ , the fourth grid G ₄ facing thereto, and the sixth grid G ₆ .
In practice, the first and second lenses Lens1 and Lens2
The ratio K=D ₁ /D ₂ of the apertures D ₁ and D ₂ is 0.3k<
Selected as 1.0. Here, k is selected to be 0.3 or more because, for example, when the neck diameter of the tube body of a color cathode ray tube is 29 mm, three electron guns corresponding to red, green, and blue are inserted into this neck. Because of the necessity, the diameter of each electron gun must be kept within 6 mm, so the larger lens diameter D ₂ is set to 6 mm.
Must be within mm. On the other hand, since D ₁ is required to be 1.8 mm or more due to beam diameter requirements, k is actually required to be 0.3 or more.

In addition, the first lens Lens1 and the second lens
Lens 2 is configured such that its lens action areas are separated from each other. Therefore, assuming that the distance between the first lens Lens1 and the second lens Lens2 is L, the distance from Lens1 to the step between the small diameter part and the large diameter part of the fourth grid _G4 is λ. ₂ , and furthermore, from this step part, the fourth and fifth grids G ₄ and
The distance to the center between G ₅ is λ ₃ , and the fourth and fifth
If λ 4 is the distance between the center between grids G ₄ and G ₅ and the center between the fifth and sixth grids G ₅ and G ₆ , then L′=λ ₂ + _{λ 3 =} L−λ ₄ /22.0D ₂ is selected.

Also, both ends of the fifth grid _G5 and the fourth and sixth grid
The distance λ ₄ between the centers of grids G ₄ and G ₆ is determined by the fact that the second lens Lens 2 constitutes an extended electric field type lens, and it is necessary to obtain a potential gradient sufficient to perform a lens action. The ratio λ ₄ /D ₂ between the distance λ ₄ and the aperture D ₂ of Lens2 is selected to be 0.3λ ₄ /D ₂ 1.0.

First and second lenses with such a configuration
By the main electron lenses consisting of Lens1 and Lens2,
The magnification and arrangement position are selected so that a crossover point created by the cathode lens system is used as an object point, and a real image thereof is formed on the fluorescent surface of the cathode ray tube.

In the above-described electron gun according to the present invention, the main electron lens is constructed by combining the first lens system Lens1 and the second lens system Lens2, and this main electron lens is a lens with small spherical aberration. Therefore, when this electron gun is used in a cathode ray tube, blooming of the beam spot on the fluorescent surface can be effectively avoided.

Next, the spherical aberration of the electron gun according to the present invention will be analyzed. This analysis uses third-order aberration theory and combined lens imaging theory.

First, the imaging relationship of the electro-optic thick lens system is explained in the fifth section.
Let's look at the diagram. Now, the focal length of this lens system is
f ₁ and f ₂ , and a plane symmetrical plane is displayed as a reference plane R. Then, the distance from this surface R to the focal point is F ₁ ,
_F2 , the distance from the reference plane R to the object point is P, and the distance to the image point is Q. Incidentally, in a cathode ray tube, there is a crossover point at a position P, and a fluorescent surface is located at a position Q. In this lens system, the following equation holds true from Newton's thick lens formula.

(P−F ₁ )(Q−F ₂ )=f ₁ ·f ₂ Furthermore, when the image magnification is M, the following equation holds true.

M=-f ₁ /P-F ₁ =Q-F ₂ /-f ₂ (1) Next, we will look at the imaging relationship including aberrations caused by this lens system.

Figure 6 shows the convergence state of the electron beam emitted from the infinitesimal point on the axis, and the paraxial light converges at the Gaussian image plane.
A ray of light emitted from the axis at an angle α becomes a circle with a radius Δr on the Gaussian image plane, and this Δr is Δr＝MCSα ³ ₀ ...(2) where α ₀ is the maximum divergence angle from the object point. C _S represents the third-order spherical aberration coefficient, which has a length dimension.

On the other hand, the potential distribution of the axially symmetric electric field of the electrostatic lens can be found by solving the following equation under given boundary conditions.

∂ ² V/∂r ² +1/r(∂V∂r)+∂ ² V∂z ² =0...(3) Here, V=V(r, z) is the potential of the axially symmetric electrostatic field where z is the axial coordinate of the lens and r is the radial coordinate. The boundary condition gives the potential on the electrodes.

As is well known, the equation of motion of an electron in this electric field is given by the following equation when the electron moves near an axially symmetrical axis.

∂ ² r／∂z＋V′／2V∂r／∂z＋V″／4Vr＝0…
...(4) Here, (r, z) represents the coordinates in the orbit of the electron. And this formula can be rewritten as follows.

d ² R/dz+3/16 (V′V) ² R=0 (5) Here, R(z) is given as follows.

R=rV ^1/4 ...(6) Additionally, a second-order differential equation generally has two independent solutions. The general solution can be expressed as follows by a linear combination of these two solutions.

U (z) = αr ₁ (z) + βr ₂ (z) ...(7) Here, r ₁ (z) and r ₂ (z) are two independent solutions of the differential equation, and α and β are is an arbitrary constant.

On the other hand, the spherical aberration coefficient of an axisymmetric lens is generally
It is given by the following formula.

C ₃ (P) = 1/16V ₀ ^1/2 ∫ ^∞ _-∞ V ^-1/2 [X ⁴ {3T ⁴ +5T′ ²
−11/2T ² T′} ⁺ X ³ X′・4TT′〕dz……( ₈ ) Here,
(z) + βr ₂ (z), T(z) = V'(z)/V(z)
It is. Now, if we select two rays as shown in Fig. 7 as r ₁ (z) and r ₂ (z), the ray U(z) emitted from the object point P shown in Fig. 8 by combining them is It is shown by the following formula.

U (z) = (P-Pi) r ₁ (z) + r ₂ (z) = v ₁ (z) + 1/Mv ₂ (z) ... (9) v1 (z) = (F- Pi) r ₁ (z) + r ₂ (
_z ), v ₂ (z) = −f ₁ r ₁ (z) This formula is: X (z) = X ₁ (z) + 1/MX ₂ (z) ...(10) ₁ V ^1/4 , X ₂ = v ₂ V ^1/4 , and [X ⁴ {3T ⁴ +5T′ ² −
11/2T ² T′}+X ³

I=I ₀ +I ₁ M ^-1 +I ₂ M ^-2 +I ₃ M ^-3 +I ₄ M ^-4
...(11) It is also known that the spherical aberration coefficient CS can be easily expressed as a function of the magnification M of the electron lens as follows. (Reference: E. Harting
and FHRead, Electrostatic Lenses Optics
(Elsevier, Amsterdam '1976)) Cs (M) = C _S0 +C _S1 M ^-1 +C _S2 M ^-2 +C _S3 M ^-3 +C
_S4 M ^-4 ...(12) Here, M is the magnification of the electrostatic lens, and the aberration coefficients C _S0 , C _S1 , C _S2 , C _S3 , and C _S4 differ depending on the electrode arrangement and voltage arrangement. Takes a value.

In this way, the spherical aberration coefficient takes different values depending on the position of the object point or image point.

Next, as shown in FIG. 9, we will calculate the change in the spherical aberration coefficient Cs due to the magnification M in a bipotential type lens using a pair of electrodes arranged with a distance S and applied with voltages V ₁ and V ₂ , respectively. If you look at it, it will look like the one shown in Figure 10. In this case, the ratio S/D between the inter-electrode spacing S and the aperture D was set to 1/5, and the ratio V ₁ /V ₂ of both applied voltages was set to 0.2 to set the acceleration mode.

Furthermore, next, we will look at the relationship between the intermediate electrode length L and the spherical aberration coefficient in a universal lens having the electrode configuration shown in FIG. Figure 12 shows the aberration coefficients C _S0 , C _S1 , C _S2 , C _S3 , and
It shows the relationship between C _S4 and L/D, in this case,
Since it is a symmetric system, C _S0 and C _S4 are equal, and C _S1
and C _S3 are equal. FIG. 13 shows the relationship between the aberration coefficient Cs and L/D when the magnification M changes. As is clear from looking at these relationships, it can be seen that the spherical aberration coefficient monotonically decreases as L/D increases, and becomes a substantially constant value at L/D 2.0. This means that the electric fields of the front lens (deceleration lens) and rear lens (acceleration lens) of the unipotential lens almost never cancel out at L/D 2.0.
That is, there is a drift region, that is, a region in which there is no lens action, between both lenses, and both lenses are independent and individual lenses, and furthermore, this L/D2.0
Spherical aberration becomes small in the range of .

Next, the two lenses Lens1 and
Let's look at the spherical aberration in the composite lens system using Lens2. Now, the spherical aberration coefficients of the two lenses are
Assuming C ¹ _S and C ² _S , the spherical aberration coefficient of the composite lens system of these two lenses, that is, the total aberration coefficient Cs, is Cs=kC ¹ _S +1/M ₁ ⁴・(V ₁ /V ₂ ) ^{3/ 2}・C ² _S ……(1
3) It can be expressed as Here, k is the front lens aperture D ₁
and the rear lens aperture D ₂ , M ₁ is the magnification of the front lens, and V ₁ and V ₂ are the voltages of the first and second electrodes. From equation (13), the aberration amount Δr can be expressed as follows.

Δr＝M ₁・M ₂ {kC ¹ _S (φ ₁ ) + 1/M ₁ ⁴ (φ ₁ ) ^3/2 C ² _S (φ
₂ )}(1/φ ₀ ) ^3/2 α ³ ₀ ...(14) Here, φ ₀ =V ₁ /V ₃ , φ ₁ =V ₂ /V ₁ , φ ₂ =
V ₂ /V ₃ .

From this equation (14), it can be seen that in order to effectively reduce the overall amount of aberration, the ratio k between the aperture D ₁ of the front-stage lens and the aperture D ₂ of the rear-stage lens is made small.

Next, we will analyze using specific numerical values. Now, the first
As shown in Figure 5, we will look at a lens system in which two bipotential lenses are placed back to back. In this lens system, in order for the first lens Lens1 and the second lens Lens2 to be independent, the distance L between both lenses must be greater than or equal to the sum of the apertures _D1 and _D2 of both lenses. , that is, LD ₁ +D ₂ . This is because, in general, in an electrostatic lens made by arranging a pair of cylindrical electrodes, the lens action area is the area that extends into each electrode from the opposing ends by a distance corresponding to the aperture. This is due to the fact that Here, there are various possible voltage relationships among V ₁ , V ₂ , and V ₃ , but as an example, let V ₁ = V ₃ and let V ₃ be the highest anode voltage in a normal color cathode ray tube. do. Also,
V ₂ is at a lower pressure than V ₃ and is in the range of 20 to 60% of V ₃ .
Incidentally, the image magnification of the main electron lens is usually 10 to 10 in color cathode ray tubes with three electron guns in either the so-called in-line type or delta (Δ) type arrangement.
The main electron lens's role is to form a real image of the crossover created by the cathode lens system on the phosphor surface, and the distance Q between this lens and the phosphor surface is the distance between the cathode rays. Q is usually in the range of 200 to 400 mm, although it varies depending on the size. Assuming that a lens is used under these conditions, a particular example is when the image magnification M of the main lens is M = 12 and Q = 300 mm (this image formation relationship is approximately the same as that of a 17-inch type color cathode ray with 90° deflection). Calculating the spherical aberration coefficient Cs of the tube (corresponding to the tube), we get
The result is shown by the curve shown by the solid line in FIG.
In this case, assuming that the diameter of the cathode ray tube neck is 29 mm, the maximum diameter D of the lens is D = 6.0 due to the geometric dimension constraints when inserting three electron guns.
mm. In FIG. 16, the horizontal axis represents the value of V ₂ /V ₃ . Spherical aberration coefficient in this case
Cs is the overall spherical aberration coefficient defined by equation (14) above, and in the figure, C ₁ and C ₂ are indicated by broken lines and chain lines.
are the respective spherical aberration coefficients C ¹ S and C ² _S of the first and second lenses expressed by the first and second terms of equation (13 ₎ above.
This corresponds to In addition, FIG. 16 shows the case where the aperture diameters of both lenses are the same (D ₁ /D ₂ =1) and the case where D 1 /D 2 = ₁ .
The values of both spherical aberration coefficients in the case of D=0.3 are shown. At any of the focus voltages shown as V ₂ /V ₃ in FIG. 16, the image magnification is 12 times and Q=
In order to form an image on the fluorescent surface at a position of 300 mm, it is necessary to change the distance L between both lenses, and each V ₂ /V ₃ to obtain the above-mentioned imaging relationship.
The values of the interval L with respect to the values of are shown in FIG. Further, FIG. 18 shows the respective image magnifications of the two lenses Lens1 and Lens2 in the imaging state of the lenses at each voltage ratio V ₂ /V ₃ . In the case of an equal-diameter lens (D ₁ /D ₂ = 1), the imaging relationship can only be obtained in the range of V ₂ /V ₃ from 0.35 to 0.37, so in Figs. 16 to 18,
The graph for D ₁ /D ₂ =1 is drawn only within this range. In contrast, in the case of a lens with D ₁ /D ₂ =0.3, an imaging relationship exists in a wide voltage range, indicating that there is a large degree of freedom in setting the focus voltage. Furthermore, as is clear from the aberration coefficient curve in FIG. 16, when the diameter D ₁ of the lens 1 on the cathode side is made smaller, the amount of aberration of this Lens 1 becomes smaller at the same voltage. That is, from this numerical result, regarding the amount of spherical aberration, the first lens
The smaller the aperture D ₁ of Lens 1, the smaller the value. In fact, if the aperture D ₁ of the first lens Lens1 is set below a certain level, other aberrations other than spherical aberration become large, so there is an optimum value for D ₁ . The aberration coefficient of the first lens Lens1 increases quadratically as the focus voltage expressed by V ₂ /V ₃ increases, but the aberration coefficient of the second lens Lens 2 tends to decrease. ing. However, as is clear from FIG. 18, as the focus voltage increases, the magnification M ₁ of the first lens Lens1 increases and the magnification M ₂ of the second lens Lens2 decreases. That is, at a high focus voltage, the lens action of the second lens Lens2 is relatively weaker than that of the first lens Lens1. In practice, the focus voltage that produces the minimum aberration coefficient and the dimensions of each lens are determined from changes in the imaging relationship with respect to changes in focus voltage, but for a lens with D ₁ /D ₂ = 0.3, , it can be seen from FIG. 16 that the total aberration coefficient Cs exhibits a minimum value when V ₂ /V ₃ is around 0.39. Incidentally, the total aberration coefficient Cs at this time is 840 mm, and the second
The aberration coefficient of the lens Lens2 is _C2 is 750mm, and the first
The aberration coefficient C ₁ of the lens Lens1 is 90 mm, and C ₁ is Cs
It is around 10%. Even in the case of a lens with D ₁ /D ₂ = 1.0, the aberration coefficient C ₁ of the first lens Lens1 is a relatively small value of about 17% of the total aberration coefficient at the focus voltage that obtains the minimum total aberration coefficient Cs. becomes.

Next, if the voltage arrangement of V ₁ is slightly changed with the two bipotential lenses shown in Fig. 15,
Let's look at how the aberration characteristics of the lens change. V ₃ is the electrode voltage at the final stage of the electron gun, so in a normal color cathode ray tube, this voltage
V ₃ is the surface voltage of fluorescence, that is, the highest anode voltage, but the voltage V ₁ can be selected to be lower than the voltage V ₃ , so this voltage V ₁ is
Let's consider the case where V ₁ < V ₃ . Like this V ₁
If <V ₃ , the divergence angle of the beam entering the first lens Lens1 becomes large, so the first lens Lens1
The amount of aberration increases. Also, this first lens
Since the lens action of Lens1 becomes weaker, it becomes necessary to increase the image magnification of the second lens Lens2 in order to maintain the same image magnification.
It is thought that the amount of aberration of Lens 2 will also increase. As a result, the overall aberration coefficient is larger in the case of V ₁ < V ₃ than in the lens with V ₁ = V ₃ mentioned above.
It is thought that the characteristics will deteriorate.

Therefore, as described above, the main electron lens is composed of the first and second lenses that are independent of each other, and the first lens is a bipotential lens with a small aberration coefficient as shown in Fig. 15. Although the configuration is the same as that of the first lens of the type, when the second lens is an extended electric field type accelerating lens as shown in the example of Fig. 4, the amount of aberration of this should be made sufficiently small. As a result, the overall aberration coefficient can be made smaller, and the overall amount of aberration can be effectively improved.

Now, as in the example shown in Figure 4, the second
Let's take a look at the characteristics when using an extended electric field accelerating lens as Lens2.

FIG. 19 shows the voltage V ₃ of the third electrode (fifth grid G ₅ ) constituting the main electron lens system in FIG.
and the ratio of the voltage V ₄ (i.e., anode voltage) of the fourth electrode (sixth grid G ₆ ), V ₃ /V ₄ , is the focus voltage, and it shows the spherical aberration coefficient with respect to the focus voltage, and this total image magnification is −12 Double the distance Q between the lens fluorescent surfaces to 300 mm, and set the lens system D to D = D ₁ = D ₂ =
6.0mm, V ₁ = V ₄ , V ₂ = 0.3V ₄ , the first
In Figure 9, curve 10 represents the overall aberration coefficient Cs when λ ₄ /D=0.871, and curves 11 and 12 represent
It shows aberration coefficients C ₁ and C ₂ of the first and second lenses Lens1 and Lens2, respectively. In addition, in FIG. 19, curve 13 shows the overall aberration coefficient Cs when λ ₄ /D=0.586, the other conditions being the same as when λ ₄ /4=0.871, and curves 14 and 15 show the first
and each aberration coefficient of the second lens Lens1 and Lens2
It shows C ₁ and C ₂ . As shown in this figure, the minimum value of the total aberration coefficient Cs is as small as approximately 500 mm, and the total aberration coefficient of the structure shown in FIG. 15 is improved by more than 40%.

Figure 20 shows total magnification M=-10, Q=300mm,
The total aberration coefficient Cs when D = D ₁ = D ₂ = 6.0, V ₁ = V ₄ and V ₂ = 0.3V ₄ is curve 16 in Fig. 20,
17 and 18 have λ ₄ /D of 0.3 and 0.443, respectively.
This is the case when it is set to 0.871.

As is clear from the curves of each coefficient Cs in FIGS. 19 and 20, V ₃ /V ₄ is 0.4 to 0.7.
The aberration coefficient Cs becomes relatively small within the range of .

In this case as well, by setting D ₁ >D ₂ , the aberration becomes smaller than the total aberration.

Further, FIGS. 21 and 22 respectively similarly show the combination lens of the first bipotential lens and the second extended electric field type lens shown in FIG. 4, with total magnification M=-12, Q=300 mm, V ₁ = V ₄ , V ₂ =
This shows the relationship between the distance L between the lenses and the image magnifications M ₁ and M ₂ of the first and second lenses with respect to V ₃ /V ₄ when the voltage is 0.3V _4. Curve 19 in FIG. 21 shows k=
When D ₁ /D ₂ is 1.0, curve 20 in the same figure is k=0.6
This is the case. As is clear from this, at any focus voltage, the distance L between the lenses is at least twice, for example, about four times, the inner diameter of the lens. Further, in FIG. 22, curves 21 and 22 indicate the values of magnification M ₁ and |M ₂ |, respectively.

As is clear from the above description, according to the electron gun configured according to the present invention, it is possible to maintain a practical imaging relationship and effectively improve aberrations.

[Brief explanation of drawings]

Figures 1 to 3 are configuration diagrams of conventional electron guns;
FIG. 4 is a configuration diagram of an example of an electron gun according to the present invention, FIGS. 5 to 22 are diagrams for explaining the present invention, and FIG. 5 is a diagram showing the imaging relationship of a thick lens system.
FIG. 6 is an optical path diagram showing the state in which spherical aberration occurs, FIGS. 7 and 8 are ray diagrams for explaining the situation, and FIG.
The figure is a diagram of the electrode configuration of a bipotential lens, Figure 10 is a curve diagram showing the relationship between magnification and spherical aberration coefficient, Figure 11 is a diagram of the electrode configuration of a unipotential lens, and Figure 12 is the distance between lenses and lens aperture. Figure 13 is a curve diagram showing the relationship between the ratio L/D and the spherical aberration coefficient Cs, Figure 13 is a curve diagram showing the relationship between L/D and Cs/D, Figure 14 is a configuration diagram of the composite lens system, Figure 1
Figure 5 is a diagram of the electrode configuration of the composite lens system, Figures 16, 17, and 18 are the spherical aberration coefficients with respect to the focus voltage when the required imaging relationship is obtained, respectively.
Figures 19, 20, 21, and 22, which show the relationship between the distance between lenses and the magnification of the two lenses, show the required image formation in the main electron lens system with the configuration shown in Figure 4, respectively. The spherical aberration coefficient, inter-lens distance, and image magnification of the two lenses are shown with respect to the focus voltage in a state where a relationship is obtained. K is a cathode, and G ₁ to G ₆ are first to sixth grids.

Claims (1)

[Claims] 1. A main electron lens system is constituted by a first lens system and a second lens system whose electron lens action areas are separated from each other, and the first lens system has a deceleration type bipotential lens structure. , wherein the second lens system has an extended electric field accelerating lens configuration, and the aperture of the first lens system is selected to be smaller than the aperture of the second lens system.