JPH06186466A - Photographing device having temperature compensation function - Google Patents

Abstract

PURPOSE:To obtain a photographing device having a temperature compensation function and capable of reducing the variation of an image forming position due to the temperature change and maintaining the excellent picture quality. CONSTITUTION:In a lens system having at least one convex lenses whose temperature coefficients of refractive index are negative, when the lateral magnification of an optical unit on the object side partitioned by an air gap where the sensitivity in the lens system is negative is defined as betai and the lateral magnification of an optical unit on the image plane side is defined as betak, the condition that (1-betai<2>).betak<2>>0.5 is satified, and the variation of an image forming position due to the temperature change is reduced by using a material in which the coefficient of linear expansion of a main body barrel 22 for holding lens holding barrels 21a, 21b is larger than that of the material of the lens holding barrels 21a, 21b holding the optical unit partitioned by the air gap.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photographing device having a temperature compensation function, for example, a photographic camera, a video camera,
Then, in a fixed focal length lens in which a secondary spectrum of axial chromatic aberration is corrected by using fluorite or anomalous dispersion glass used for a television camera or the like, a lens holding barrel and a main body holding the lens holding barrel The present invention relates to an image pickup apparatus having a temperature compensation function that suppresses a change in image forming position (image forming performance) due to a temperature change by using a material having an appropriate linear expansion coefficient for a lens barrel.

[0002]

2. Description of the Related Art In conventional fixed focal length lenses used for photographic cameras, video cameras, television cameras and the like, anomalous dispersion glass is used in addition to ordinary dispersion optical glass for chromatic aberration correction. ing.

In particular, a telephoto lens having a long focal length and a fixed focal length lens for a three-plate video camera are often constructed by using anomalous dispersion glass and fluorite in order to suppress axial chromatic aberration.

For example, the flange back is converted into air (in
In a lens system of a three-plate type broadcasting camera whose air is about 48 mm, the axial chromatic aberration is B (blue light) -G (green light) =
30 μm, R (red light) -G (green light) = about 4 μm.

In such a case, the zoom lens can relatively easily correct chromatic aberration in accordance with this standard.

However, in a fixed focal length lens, it is necessary to make the entire lens system more compact than in a zoom lens, so that it is not possible to use only glass having a normal secondary dispersion of axial chromatic aberration. It is difficult to correct it well. Therefore, in many cases, anomalous dispersion glass, fluorite, etc. are often used.

[0007]

Generally, in optical glass having ordinary dispersibility, the temperature of the material changes when the environmental temperature changes, which causes a change in the refractive index and a change in the focal length of the element. It has optical properties. As a result, there is a problem that the image forming state such as the image forming position on the image forming surface changes.

The temperature coefficient with respect to the refractive index of optical glass (the ratio of the change in the refractive index to the change in temperature) is generally positive.
Therefore, a convex lens (positive lens) and a concave lens (negative lens)
By appropriately combining and to form the lens system, it is possible to cancel the change in the imaging position due to the temperature change to some extent.

On the other hand, as described above, anomalous dispersion glass used in a telephoto lens or the like (for example, FPL51 and FPL5 in a catalog manufactured by Ohara Optical Glass Co., Ltd.)
(2, FPL53, PHM52, etc.) and fluorite have a negative temperature coefficient of refractive index. Therefore, the optical influences of the convex lens and the concave lens are overlapped with each other, and the change of the image forming position becomes very large when the temperature changes.

As a result, there is a problem in that the optical performance is greatly deteriorated due to inconveniences such as image blurring due to temperature change and displacement of the distance scale during focusing.

Therefore, in the case of a lens system using anomalous dispersion glass, fluorite, or the like, there is a need for a means for suppressing the fluctuation of the image forming position when the temperature changes by some correction means.

In order to solve the above-mentioned problems, the present invention has a negative sensitivity (ratio of change in image forming position with respect to change in air gap) (when the air gap is widened, the image forming position changes to the lens side). Direction) and the absolute value of which is relatively large, the entire lens system is divided into a plurality of optical units at the boundary, and the material of the lens holding barrel for holding the plurality of divided optical units and the lens. By using a material having an appropriate linear expansion coefficient as the material of the main body barrel that holds the holding barrel, even if the temperature changes and the refractive index of each lens constituting the lens system fluctuates, the imaging position It is an object of the present invention to provide an image pickup apparatus having a temperature compensation function, which is capable of constantly maintaining high optical performance by reducing the fluctuation of

[0013]

A photographing apparatus having a temperature compensation function of the present invention is a lens system having at least one convex lens having a negative temperature coefficient of refractive index, and the sensitivity in the lens system is negative. When the lateral magnification of the optical unit on the object side is β _i and the lateral magnification of the optical unit on the image plane side is β _k with the air space as the boundary, then (1-β _i ² ) × β _k ² > 0 ........................ (1) Hold the lens holding barrel more than the linear expansion coefficient of the material of the lens holding barrel that holds the optical unit divided by the air gap as the condition (1). It is characterized by using a material having a large linear expansion coefficient of the main body barrel to reduce the amount of fluctuation of the imaging position due to temperature change.

[0014]

EXAMPLE 1 FIG. 1 is a schematic view of a main part of a lens barrel main body having a lens system of a numerical example to be described later in Example 1 of the present invention.

In the figure, 1, 3, 6, 7, 9, 11,
Reference numerals 13 and 14 denote convex lenses (positive lenses), which are made of extraordinary dispersion glass. By using these, the secondary spectrum of the axial chromatic aberration is satisfactorily corrected.
The lens 1 is made of FPL03, 3 is PHM52,
6,9,11,14 are FPL01, 7 and 13 are FPL0
The temperature coefficient of the refractive index is negative in both cases.

Reference numerals 2, 4, 5, 8, 10, and 12 are concave lenses (negative lenses), which are made of optical glass having a larger dispersion than general glass, and are combined with the positive lens described above to balance chromatic aberration. Correcting. The temperature coefficient of the refractive index of the material of these concave lenses is positive.

The lens system in this embodiment is sensitive to the air gap (ratio of the change in the image forming position to the change in the air gap).
Is divided into two subsystems (optical unit) of a front lens unit A and a rear lens unit B with an air gap D9 between the concave lens 5 and the convex lens 6 having the largest negative value as a boundary. .

In this embodiment, if the conditional expression (1) described later is satisfied, the position (air interval) at which the lens system is divided is not limited to this position.

Reference numeral 21a is a lens holding barrel for holding the front lens unit A, and 21b is a lens holding barrel for holding the rear lens unit B.

It is desirable that the material of the lens holding barrels 21a and 21b has a linear expansion coefficient similar to that of glass.

In this embodiment, iron (coefficient of linear expansion = 11.8 ×
10 ^-6 : Numerical values from the science chronology, the same applies below).

The lens holding lens barrel 21 is made of iron having a linear expansion coefficient similar to that of the glass as the lens holding member.
Since a and 21b are in direct contact with the lenses 1 to 14 made of anomalous dispersion glass or optical glass, if the difference in linear expansion coefficient with the glass is large, the glass will break when a large temperature change occurs, for example. This is to prevent this.

The linear expansion coefficient of glass is 5 × 10 ⁻⁶ to 15
It is about 10 ⁻⁶ . In particular, glass with anomalous dispersion is
Care must be taken as it has a large linear expansion coefficient and is brittle and easily cracked. The material of the lens holding barrel is preferably within ± 70% of the linear expansion coefficient of the lens material used.

Reference numeral 22 denotes a main body barrel, which is a lens holding barrel 2.
It holds 1a and 21b. The body barrel 22 is made of a material such as zinc (coefficient of linear expansion = 30.2 × 10 ⁻⁶ ) which is larger than the linear expansion coefficient of the lens holding barrel. It is desirable that the ratio of the linear expansion coefficient between the main body barrel and the lens holding barrel is about 1.5 times or more.

Reference numeral 23 is a stop, 24 is an image plane, and L1 and L2 are spans of lens barrel materials. In this embodiment, L1 is used.
= 87 (mm) and L2 = 100 (mm).

In this embodiment, when a temperature change is caused by utilizing the difference in expansion coefficient between two kinds of lens barrel materials having different linear expansion coefficients, the refractive index of the glass lens fluctuates and the image forming position. Even if the change occurs, the lens barrel material expands and the air gap with negative sensitivity changes, so that the amount of fluctuation of the image forming position is suppressed to be small.

In the present embodiment, the sensitivity when the air distance from the i-th lens surface of the i-th surface to the (i + 1) -th lens surface counting from the object side is changed is obtained as follows.

That is, the lateral magnification of the partial system (front lens unit A) on the object side of the i-th lens surface is β _i , and the lateral magnification of the partial system (rear lens unit B) from the (i + 1) th lens surface to the final lens surface. Is β _k , the sensitivity M is M = − (1-β _i ² ) × β _k ² .

In order to satisfactorily correct the image forming position by utilizing the difference in linear expansion coefficient between the two lens barrel materials as in the present embodiment, it is preferable that the sensitivity M is large. That is, in this embodiment, two lens systems are arranged at an air gap that satisfies the condition that the value of the sensitivity M is (1-β _i ² ) × β _k ² > 0.5 (1). It is divided into subsystems.

Conditional expression (1) defines the value of the sensitivity of the air gap when the lens system is divided into two subsystems. If the conditional expression (1) is not satisfied, it becomes difficult to correct the fluctuation of the imaging position due to the temperature change to a small extent, and it becomes difficult to maintain a good image quality, which is not preferable.

Here, the effects of this embodiment will be described using specific numerical values. The lateral magnification β _i of the front lens unit A in this embodiment is β _i = 1.053 × 10 ⁻²⁸ , and the lateral magnification β _k of the rear lens unit B is β _k = −0.950, so the sensitivity M is M = ( 1−β _i ² ) × β _k = 0.902. This value satisfies the conditional expression (1) described above.

That is, when the front lens unit A closer to the object side than the air gap moves toward the object side and the air gap widens by Δ, for example, the back focus becomes shorter by -0.902 × Δ.

Now, the air gap between the concave lens 5 and the convex lens 6 is 25 according to the numerical example, and the air gap D9 at this time is
When the temperature is changed from 20 ° C. to 40 ° C. and the correction amount P of the image forming position is calculated, P = 25 × (− 0.9) x 30.2 x 10 ^-6 x 20 + 8
7 x (-0.9) x (30.2-11.8) x ^10-6 x
20 + 100 × (−0.9) × (30.2-11.8)
× 10 ⁻⁶ × 20 = −75.5 μm.

On the other hand, the temperature changes (20 ° C to 40 ° C).
C) The amount of change in the imaging position due to the change in the refractive index of the lens is approximately 80 μm.

That is, the final amount of change in the image forming position according to the present embodiment is 4.5 μm from the above, and this value is within the allowable range of the present apparatus, and there is almost no problem in actual use.

As described above, in the present embodiment, the air gap is appropriately changed by effectively utilizing the difference in the expansion coefficient between the two lens barrel members having different linear expansion coefficients, so that the result due to the temperature change can be obtained. The fluctuation of the image position can be suppressed to a small level, thereby maintaining good image quality.

In this embodiment, the lens holding barrel 2
Although iron is used as the material of 1a and 21b, a material having a linear expansion coefficient similar to that of glass such as aluminum or permalloy may be used, and brass or bronze is used instead of zinc as the material of the main lens barrel 22. The present invention can be applied in the same manner as the above-mentioned embodiment even if a material having a large linear expansion coefficient such as a synthetic resin is used.

Next, numerical examples of the lens system shown in FIG. 1 will be shown. In the numerical examples, Ri is the radius of curvature of the i-th lens surface in order from the object side, Di is the i-th lens thickness and air gap from the object side, and Ni and νi are respectively from the object side of the i-th lens. Refractive index and Abbe of glass, FNo is aperture ratio, f is focal length, ω is half angle of view, and fb is back focus.

(Numerical Example) FNO = 1: 1.4 f = 100 ω = 2.90 fb = 22.20 R 1 = 175.79 D 1 = 10.00 N 1 = 1.438750 ν 1 = 94.97 R 2 = -131.61 D 2 = 0.50 R 3 = 65.48 D 3 = 3.00 N 2 = 1.712995 ν 2 = 53.84 R 4 = 56.68 D 4 = 13.00 N 3 = 1.618000 ν 3 = 63.39 R 5 = 2474.82 D 5 = 29.29 R 6 = -95.33 D 6 = 2.00 N 4 = 1.620410 ν 4 = 60.28 R 7 = 38.94 D 7 = 8.55 R 8 = -22.45 D 8 = 4.80 N 5 = 1.785896 ν 5 = 44.19 R 9 = 78.35 D 9 = 19.00 R10 = ∞ D10 = 6.00 R11 = -251.22 D11 = 9.69 N 6 = 1.496999 ν 6 = 81.61 R12 = -32.09 D12 = 0.70 R13 = -129.15 D13 = 9.21 N 7 = 1.455999 ν 7 = 90.31 R14 = -36.53 D14 = 2.20 N 8 = 1.691002 ν 8 = 54.84 R15 = -63.40 D15 = 0.50 R16 = 140.18 D16 = 10.15 N 9 = 1.496999 ν 9 = 81.61 R17 = -58.00 D17 = 2.20 N10 = 1.696797 ν10 = 55.53 R18 = -236.52 D18 = 0.50 R19 = 75.48 D19 = 6.98 N11 = 1.496999 ν11 = 81.61 R20 = -865.55 D20 = 43.00 R21 = 89.26 D21 = 2.50 N12 = 1.834807 ν12 = 42.72 R22 = 45.09 D22 = 0.86 R23 = 52.97 D23 = 9.01 N13 = 1.455999 ν13 = 90.31 R24 = -112.94 D24 = 0.50 R25 = 44.78 D25 = 4.83 N14 = 1.496999 ν14 = 81.61 R26 = 106.33 D26 = 5.00 R27 = ∞ D27 = 30. 00 N15 = 1.603420 ν15 = 38.01 R28 = ∞ D28 = 16.20 N16 = 1.516330 ν16 = 64.15

[0040]

According to the present invention, as described above, the lens system is divided into a plurality of optical units with an air gap having a negative sensitivity and a relatively large absolute value as a boundary, and the divided optical units. By using a material having an appropriate linear expansion coefficient for the lens-holding barrel that holds the lens and the main-body barrel that holds the lens-holding barrel, it is possible to suppress fluctuations in the imaging position due to temperature changes. As a result, it is possible to achieve an image pickup apparatus having a temperature compensation function capable of maintaining good image quality.

[Brief description of drawings]

FIG. 1 is a schematic view of a main part of a first embodiment of the present invention.

[Explanation of symbols]

1,3,6,7,9,11,13,14 Convex lens (positive lens) 2,4,5,8,10,12 Concave lens (negative lens) 21a, 21b Lens holding lens barrel 22 Main lens barrel 23 Aperture 24 Image plane

Claims (1)

[Claims] 1. In a lens system having at least one convex lens having a negative temperature coefficient of refractive index, the lateral magnification of an optical unit on the object side is set at the boundary of an air gap having a negative sensitivity in the lens system. β _i , where the lateral magnification of the optical unit on the image plane side is β _k , the condition of (1-β _i ² ) × β _k ² > 0.5 is satisfied, and the air gap is used as a boundary. A material having a larger linear expansion coefficient than the material of the lens holding barrel that holds the optical unit than the linear expansion coefficient of the main body barrel that holds the lens holding barrel is used. An imaging device having a temperature compensation function characterized by reducing the number of