JPS59176716A - Condenser lens - Google Patents

Abstract

PURPOSE:To obtain a condenser lens which has an excellently compensated curvature of field by specifying the conditions of a lens group of six elements having positive, positive, negative, positive, positive, and negative refracting power successively from an object side. CONSTITUTION:This lens system has six-element constitution of the 1st positive lens, the 2nd positive lens, the 3rd biconcave lens, the 4th biconvex lens, the 5th positive lens having a large-curvature surface on the object side, and the 6th negative lens having a large-curvature surface on the image side successively from the object side. This lens system meets requirements shown by inequalities I -IV, wherein (f) is the focal length of the whole system and ri is the radius of curvature of the (i)th surface.

Description

[Detailed Description of the Invention] (Field of Application of Dashiba) This invention has a large numerical aperture and is capable of scanning with a condensing lens with well-corrected step curvature, especially an optical deflector such as a rotating polygon mirror. The present invention relates to a condensing lens suitable for condensing a luminous flux onto a sub-image recording object.

(Prior Art) In recent years, as video discs and digital audio discs have become widespread, many condensing lenses with large apertures and diffraction-limited performance have been proposed.

However, in the optical system for playing back video discs and digital audio discs, the condensing lens is moved in the optical axis direction and 7 focussing is always performed, so even if the edge surface is curved, out-of-focus does not occur, and the edge surface The appearance of curvature is disapproved.

For this reason, it is not possible to obtain the necessary angle with these ■ lenses.

Furthermore, although the upward curvature of the microscope lens is corrected, the position of the front focal point is located very centrally from the front surface of the lens.

For this reason, when using a microscope lens for the purpose of condensing the radial light scanned by a rotating polygon mirror or carbanomirror onto a thousand-sided recording medium, in order to prevent clarification of the light flux, the incident light flux must be compared to the lens shape. This results in a need to increase the thickness and reduce the efficiency of light use.

Furthermore, in order to use it as an optical 7-Lier conversion lens, it is necessary to place an object at the object side focal point, so it is very difficult to substitute a microscope lens as a 7-Lier conversion lens.

(Objective of the Invention) This invention has a large numerical aperture of N, A = 0.45, has well-corrected tufted hooks, has diffraction-limited performance, and is used as a 7-lier transformation lens. The aim is to obtain a condensing lens that has sufficient performance.

(Structure of the invention) As shown in FIG. 5th point of stop pointing towards the object side
The lens has a six-lens configuration consisting of a negative sixth lens with the surface with strong curvature facing toward the edge, where f: focal length of the entire system rl: radius of curvature of the first surface -2,5f <rs < -1,Of・・・・・・(
1) 0, 5 f < r, < 0.9 f
−(2)1, Of < r <
4. Of -... (3) 0 0, 5 f< (r6+r12)/2 < 1. O
f-.-(4) ■It satisfies the condition.

Condition (1) is for properly correcting spherical aberration. If the upper limit is exceeded, high-order positive spherical aberration will occur, and the residual spherical aberration in the intermediate annular zone will be large.If the lower limit is exceeded, the spherical aberration will be undercorrected, and it will be necessary to try to correct this forcefully. The sine condition becomes true.

Condition Q) is a condition for correcting astigmatism.

If the upper limit is exceeded, astigmatism will be overcorrected. On the other hand, if the lower limit is exceeded, astigmatism becomes difficult to compensate for, and to compensate for this, it is necessary to extremely lengthen the air distance d6 between the third lens and the fourth lens. Undesirable.

Condition (3) is for correcting the sine condition. If the upper limit is exceeded, the sine condition will be over-corrected; on the other hand, if the lower limit is exceeded, the sine condition will be under-corrected. If this is attempted to be corrected using the rib surface, higher-order spherical aberration will occur, and residual annular aberration will become larger.

Condition (4) is for compensating for caravan curvature.

If the upper limit is exceeded, the edge surface curvature will be insufficiently corrected and the angle of view with diffraction-limited performance will be small, making it impossible to achieve the object of the present invention. If the lower limit is exceeded, higher-order spherical aberration,
If the coma aberration is large, the lens cannot be bent into a large aperture.

The lens of the present invention preferably satisfies the following 0 conditions.

0, 3 f < d6 < 0.7 f −・
(5) The sixth lens of the υ lens of the present invention not only corrects the field curvature θ but also has the function of moving the front focal point as far toward the object side as possible. However, since the power of the composite thread of the fourth to sixth lenses is positive, increasing d6 means moving the front focal position to the side with respect to the first surface of the lens. Become. Therefore,
d6 is the upper limit, so get big with rotating polygons and galvano mirrors.
It is disadvantageous to use it for the purpose of concentrating the FC light beam scanned by etc. on the body, and it is not suitable for industrial use.
r is limited. On the other hand, if the lower limit is exceeded, higher-order spherical aberration occurs, and even if you try to forcefully correct it, multiple spherical aberrations will appear on the spherical aberration curve. An inflection point occurs, and residual annular spherical aberration becomes large.

(Example) Below, the foil array of this f''υ lens system will be shown.

Iron medium, rl, d4, ni, j/i follow well-known usage,
d.

is the axial thickness ratio of the cover glass (refractive index 1.511-15); The air interval on the υ axis is increased to the plane of and the front focal point, and fB%f
, the direction from the reference point toward the veranda is the stop.

Example f=1. o NA-0,45M-Odc-0,03f
B-0,3363ff=-0,1452(r6+r12
)/2=0.7 1 6 s Example 2 j-1, ONA=0.45 M=Ode=0.03f
B=0.3127 ff-0,1929('6+'+
2) / 2,000, 6384 barley 3 /-1, ONA=0.45 M=Od0=0.03f
H theory 0.2940 //=0.0691 (r6+r,
2)/2=0.6190 Example 4 1. QNA SE 0.45M 雛Q d, = 0.
037B=0.3127 f,=-0,3397(r
6+r, 2)/2=0.7173 Example 5 f-1,ONA-0,45M-Odc-0,03fH=
0.1838 f (= 0.3877 (r6,000 r,
2 )/2=(1,8s 5 9 (Invention Q Effect) As seen in the aberration diagrams shown in FIGS. 2 to 6, the lens system of this invention has excellent extraction of various aberrations, especially at the edges. The Menwan curve is extremely small and has a focal length of 10m.
It has diffraction-limited performance within a large image circle of 1.2 mmφ when yy+.

In the case of a condensing lens for a video disk reproduction phase, the image circle with diffraction-limited performance is at best 0.4 mm diameter due to caravan curvature, but the effect of this invention is quite remarkable. be.

[Brief explanation of the drawing]

Fig. 1 is a cross-sectional view of the lens thread of the present invention, and Figs. 2, 3, 4, 5, and 6 are the first embodiment and It is a convergence diagram of the 2nd practical, the 4th practical, and the 5th actual practical. Patent applicant: Konishi Rokuyohei Kogyo Co., Ltd. Publisher: Patent attorney: Fumi Sato Tsudai
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Claims (1)

[Claims] From the object side, a positive lens, a positive second lens, and a biconcave third lens.
It has a six-element configuration consisting of a biconvex fourth lens, a positive fifth lens with its surface with strong curvature facing the object side, and a negative sixth lens with its surface with strong curvature facing the edge side, f: Focal length ri of the entire system: -2,5f < rs < -1, OfO, 5f when curvature # of the first surface - diameter
<re < 0-9f1, Of<rho
<4. Of o, 5 f< (rb+”12)4 (Condensing lens whose % enemy is to satisfy the condition of 1-Of