JPS61245130A - Cloud preventing device - Google Patents

Abstract

PURPOSE:To prevent effectively a lens from being clouded with extremely simple constitution by fitting a transparent member which has a smaller heating value than a lens to the front surface of the lens and forming an air layer which has small heat conductivity between the lens and transparent member. CONSTITUTION:A preventing device 4 which prevents the surface 30a of the 1st lens 30 from being clouded up is fitted detachably atop of a lens barrel 2, and a film 6 of acryl which has the small heating value is fitted to the holding ring 5 for the preventing device to form the air layer 7 which has the small heat conductivity between the lens 30 and film. Therefore, when the lens 30 is exposed to, for example, outside air of high temperature, the film 6 rises in temperature to the outside temperature speedily, but the surface temperature of the lens 30 does not vary so much and water becomes hard to condensate on the surface of the lens 30. Consequently, the extremely simple constitution prevents effectively the lens from being clouded up.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field of the Invention) The present invention relates to an anti-fogging device for preventing fogging on the surface of an optical member.

(Background of the Invention) Conventionally, techniques for preventing fogging on the surface of an optical member (for example, the surface of a lens on the outside air side of a photographic lens) include (1) optical members in which a surfactant or a hydrophilic substance is brought into contact with the outside air; (2) A method of preventing fogging by coating the surface of an optical member so that the moisture attached to the surface forms a film rather than turning into droplets; (2) a method of heating the surface of an optical member that is in contact with the outside air with hot rays or hot air; There is a method of preventing fogging by preventing moisture in the outside air from condensing on the surface of an optical member.

However, in the above-mentioned conventional technology (1), there are problems in that the mechanical strength of surfactants and hydrophilic substances is weak, and light interference occurs due to a film of moisture attached to the surface of the optical member. There was a problem in that optical performance deteriorated due to deterioration of transmittance.

Further, in the above-mentioned conventional technique (2), since a device for the heating is required, the entire device becomes large and complicated, leading to an increase in manufacturing cost.

(Object of the Invention) The present invention has been made by focusing on such conventional problems, and has an extremely simple structure and can prevent fogging on the surface of an optical member without deteriorating optical performance. The purpose is to provide an anti-fog device.

(Summary of the Invention) The gist of the present invention to achieve the above object is to provide an anti-fogging device for preventing fogging on the surface of an optical member, in which the amount of heat required to raise a unit volume by a unit temperature is A smaller transparent member is attached to the optical member in order to isolate the surface of the optical member from the outside air, and a calendar whose thermal conductivity is smaller than that of the optical member is provided between the transparent member and the surface of the optical member. The invention resides in an anti-fogging device characterized by the following.

In the anti-fogging device, when the optical member comes into contact with high temperature outside air, the transparent member has a smaller amount of heat (the amount of heat required to raise a unit volume by a unit temperature) than the optical member. The temperature quickly approaches the temperature of the outside air, and the temperature of the outside air on the surface of the optical member does not drop much.

Therefore, moisture condensation is less likely to occur on the surface of the optical member, and clouding is prevented from occurring on the surface of the optical member.

(Example) Each embodiment of the present invention will be described below based on one drawing.

1 and 2 show a first embodiment of the invention.

As shown in FIG. 1, a lens barrel 2 is attached to a camera l by a mount portion 2a. A photographing lens 3 is held in the lens barrel 2.

An anti-fogging device 4 is attached to the tip of the lens barrel 2 to prevent the surface 30a of the lens 30, which is the optical member of the photographic lens 3 that is closer to the outside air, from fogging up.

This anti-fogging device 4 includes a retaining ring 5 that is detachable from the tip of the lens barrel 2, and an acrylic film 6 attached to the retaining ring 5 to isolate the surface 30a of the lens 30 from the outside air 8. It consists of an air layer 7 formed between the acrylic film 6 and the surface 30a of the first lunches 30.

The acrylic film 6 constitutes a transparent member in which the amount of heat required to raise a unit volume by a unit temperature is smaller than that of the lune 30, and is formed in the shape of a disc, and is attached to the inner circumference of the retaining ring 5. is fixed to.

The air layer 7 constitutes an ephemeris whose thermal conductivity is smaller than that of the lunes 30.

The thermal properties of acrylic, which is the material of the acrylic film 6, and the thermal properties of glass, which is the material of the lune 30, are shown in Table 1 for reference.

Table 1 The operation of the anti-fogging device 4 having the above structure will be explained with reference to FIGS. 2 and 3.

Here, FIG. 2 shows the acrylic film 6 viewed from the outside air 8 side.
, the air layer 7, and the second lune 3o are arranged in this order, and the vertical axis shows the temperature, and the horizontal axis shows the position of each member in the optical axis direction.

Figure 3 is used for comparison with Figure 2;
The second r! It is a temperature distribution diagram similar to lI.

Photographing lens 3 of camera l shown in FIG. 1 whose temperature is Tl
When the anti-fogging device 4 attached to the front surface of the device, also at a temperature of TfL, comes into contact with the outside air 8 having a temperature Th, the anti-fogging device 4 attached to the front surface of the outside air 8. The temperature distribution of the acrylic film 6, the air layer 7, and the lune 30 is as shown in FIG. 2(a).

Also, when there is no acrylic film 6, the outside air 8 immediately after coming into contact with the outside air 8. The temperature distribution of the lunches 30 is as shown in FIG. 3 (JL).

Here, in the figure, T2n is the temperature at the interface between the outside air 8 and the acrylic film 6, and T0n is the temperature at the interface between the outside air 8 and the acrylic film 6.
This is the temperature at the interface with 0. Also, temperature 72a, T0
The saturated vapor pressure of outside air 8 at n is P 2a,
Let it be P 3a.

That is, as shown in FIG. 2(a) and FIG. 3(a),
Immediately after the photographic lens 3, the anti-fogging device 4, or the first lens 30 is brought into contact with the outside air 8, there is no time for heat to flow from the outside air 8 into the acrylic film 6 or the second lens 30, so that the temperature T 2a , T 3a has the relationship 72a'=T 3a': T 1 , and the saturated vapor pressures P2a, P3a at this time
Is it P2a? The relationship is P3a.

If Δ seconds have passed since the photographing lens 3, the anti-fogging device 4, or the lens 30 came into contact with the outside air 8, the temperatures T2a and T0n each become the temperature T2.
b, becomes Tab.

In addition, the temperature distribution obtained by subtracting Δ seconds after the photographing lens 3 and the anti-fogging device fi4 come into contact with the outside air 8 is shown in FIG. 2(b).
The temperature distribution at Δ seconds after the photographing lens 3 comes into contact with the outside air 8 is shown in FIG. 3(b).

The temperatures T2b and T3b at this time are 1 sentence<T3b<T2b<Th This is the relationship.

This is due to the following reasons.

That is, (1) as shown in Table 1, acrylic has a lower thermal conductivity than glass, and the air layer 7, which is a layer with a lower thermal conductivity than the first lune 30, is formed between the acrylic film 6 and the second lune 30. Because the acrylic film 6 is interposed in between, it is difficult for the surface heat to be transmitted to the inside compared to the glass lunches 30, and it is difficult for the heat to escape from the surface to the inside, as shown in (2) Table 1. For acrylic, the product of specific heat and specific weight, that is, the amount of heat required to raise a unit volume by a unit temperature, is smaller than that of glass.

In addition, since the acrylic film 6 can be made sufficiently thinner and smaller in volume than the second rung 30, the temperature of the acrylic film 6 increases more with less heat flowing in than the second rung 30.

If the saturated vapor pressures of the outside air 8 at the temperatures T2b and T3b are P2b and P3b, respectively, then T
From the relationship 3b<T 2b, P2b and P3b are.

P 3b< P 2b , and moisture condensation occurs on the surface of the acrylic film 6 less than on the surface of the lunches 30 without the acrylic film 6, and therefore it is less likely to become cloudy. .

In the first embodiment, instead of the air layer 7, a layer having a lower heat transfer coefficient than the first lunion 30 is used as the air layer 7.
The anti-fogging device may be constructed by vapor depositing a transparent member on the surface of the vapor deposited layer, and forming a transparent member on the vapor deposited layer with a smaller amount of heat required to raise a unit volume by a unit temperature than the first lens 30. .

Next, a second embodiment of the present invention will be described based on FIG.

In this second embodiment, the anti-fogging device 4 is constructed by arranging a reinforced glass 9 having high mechanical strength near the acrylic film 6 to supplement the mechanical strength of the acrylic film 6. .

Further, the anti-fogging device 4 according to the second embodiment is also attached to the tip of the lens barrel 2 in the same manner as in the first embodiment, and prevents the surface 30a of the lens (optical member) 30 from fogging. It is something.

As shown in FIG. 4(a), an acrylic acid film 6 and a reinforcing glass 9 are attached to the retaining ring 50.

The acrylic acid film 6 and the reinforcing glass 9 are arranged with an air layer 70 in between by a spacer lO, and a presser ring t
It is fixed to the retaining ring 50 by i. The air layer 70 is
It is thinner than the air layer 7.

The retaining ring 50 is formed with a threaded portion 50a that is screwed into a threaded portion (not shown) formed at the tip of the lens barrel 2.

In the anti-fog device M4 according to the second embodiment having the above configuration, when an external force P is applied to the acrylic acid film 6 as shown in FIG. 4, the acrylic acid film 6 deformed by the external force P is Since it comes into contact with the reinforcing glass 9, the acrylic acid film 6 is prevented from being damaged and the mechanical strength of the acrylic acid film 6 is supplemented.

Furthermore, since the air layer 70 is thinner than the air layer 7, natural convection of air inside the air layer 70 is less likely to occur than inside the air layer 7.

Therefore, in the case of this second embodiment, the amount of heat transferred from the acrylic acid film 6 to the air layer 70 is smaller than in the first embodiment, and the heat of the acrylic acid film 6 is less likely to be lost. The acrylic acid film 6 easily follows temperature changes in the outside air 8, and the surface of the acrylic acid film 6 is less likely to become cloudy.

Note that the anti-fog device 4 of each of the above embodiments is not limited to the lens 30 of the lens barrel 2 of the camera I.

Needless to say, the present invention can be applied to other optical members.

For example, by attaching the anti-fogging device 4 to the eyepiece of a camera, it is possible to prevent the cold surface of the eyepiece from fogging up due to water vapor emitted from the human body.

In each of the above embodiments, acrylic was used as the material of the film 6 as a transparent member, but the material of the film 6 is not limited to acrylic. It is preferable that the material has a smaller amount of heat and thermal conductivity than the first lens 30 as an optical member, and is transparent.

(Effects of the Invention) According to the anti-fogging device according to the present invention, a transparent member that requires less heat to raise a unit volume by a unit temperature than an optical member is used to isolate the surface of the optical member from the outside air. By simply attaching it to an optical member and providing a layer with a lower thermal conductivity than the optical member between the transparent member and the surface of the optical member, the optical member can be It can prevent fogging,
The configuration is extremely simple and manufacturing costs can be reduced.

Moreover, the optical performance of the optical member is not deteriorated.

Furthermore, by configuring the transparent member to be removably attached to the optical member, it is possible to provide an easy-to-handle anti-fogging device, and when used in a photographic lens of a camera, etc., it can be handled in the same way as a general filter. It is extremely convenient.

[Brief explanation of drawings]

1 and 2 show a first embodiment of the present invention, FIG. 1 is a partial sectional view showing only the lens barrel of the camera, and FIG. FIG. 2(a) is a temperature distribution diagram of each optical member immediately after contact with the outside air. Figure 2 (b) is a temperature distribution diagram Δ seconds after contact with the outside air, and Figure 3 is used for comparison with Figure 2. Figure 3 (a) is a temperature distribution diagram similar to Figure 2 when the film (transparent member) is removed, Figure 3 (a) is a temperature distribution diagram immediately after contact with outside air, and Figure 3 (b) is a temperature distribution diagram after contact with outside air. Fig. 4 is a cross-sectional view showing the main part of the second embodiment of the present invention, and Fig. 4(a) is a temperature distribution diagram after Δ seconds from Δ. FIG. 4(b) is a cross-sectional view showing a state in which an external force is applied to the center of the acrylic acid fill (transparent member). 4... Anti-fog device 6... Acrylic acid film (transparent member) 7; 70.
... Air layer (layer with lower thermal conductivity than the optical member) 8... Outside air 30... Runes (optical member) Fig. 5 (θ) Cylinder 4 (b) Fig.

Claims (3)

[Claims] (1) In an anti-fogging device that prevents fogging on the surface of an optical member, a transparent member that requires a smaller amount of heat to raise a unit volume by a unit temperature than the optical member is used to isolate the surface of the optical member from the outside air. 1. An anti-fogging device characterized in that the anti-fogging device is attached to the optical member, and a layer having a thermal conductivity lower than that of the optical member is provided between the transparent member and the surface of the optical member. (2) The anti-fogging device according to claim 1, wherein the transparent member is removably attached to the optical member. (3) The anti-fogging device according to claim 1, wherein the transparent member is made of a material having a lower thermal conductivity than the optical member.