JPH0321885B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a plastic lens holding mechanism, and more particularly to a lens holding mechanism that holds a plastic lens between a lens barrel mounting surface of a lens barrel and a presser ring.

Figures 1A-1E illustrate examples of the prior art. When fixing the plastic lens 1 to the metal lens frame 2, the lens 1 is brought into contact with the lens frame mounting portion 4 through the lens frame fitting portion 3. Next, screw in the holding ring 5 having the holding ring outer threaded part 6 that engages with the internal threaded part 7 of the lens frame, and as shown in FIG. 1B, the lens holding ring contact part 8
is brought into contact with the lens 1 and the lens 1 is fixed within the lens frame 2.

If the lens 1 and lens frame 2 assembled at room temperature are brought to a high temperature state, the linear expansion coefficient of the material forming the lens 1 is larger than that of the material of the lens frame 2 and the holding ring 5, so the lens 1 The gap between the outer peripheral surface of the lens frame fitting portion 3 and the lens frame fitting portion 3 becomes smaller. Furthermore, since there is no gap at the abutting portion 8 of the lens holding ring 5 shown in FIG. 1B during assembly, the surface of the lens 1 at the abutting portion 8 is depressed due to expansion of the lens 1.

That is, when the temperature increases, the lens 1 relatively expands in the radial direction. However, the first B of the lens holding ring 5
In the abutting portion 8 shown in the figure, since there is no gap during assembly, expansion is restricted and thermal stress is generated inside the lens. The lens begins to deform in the direction of the optical axis without restriction. A cross section of the lens 1 in the axial direction including the optical axis is shown in FIG. 1C, and since the length of the chord AB is constant,
The length of arc AB increases, and the arc is exaggerated with a dotted line.
The shape becomes AO′B, and the radius of curvature becomes smaller. Assuming that the length of the arc at room temperature is AB, the length of the arc at t° C. higher than room temperature is A'B', and the coefficient of linear expansion of the lens is α, the approximate equation is given by the following equation.

A'B'=AB・(1+αt) Next, if the lens 1 and the lens frame 2 shown in FIG. shrinks relative to. At this time, since the outer periphery of the lens 1 is restricted by the contact portion 8 of the holding ring 5, thermal stress is generated inside the lens, causing it to deform in the optical axis direction. As shown in FIG. 1D, the length of the arc AB is reduced to an arc length AO'B indicated by a dotted line. If the arc length AB is at room temperature, the arc length is A″B″ when the temperature is t°C lower than normal temperature, and the linear expansion coefficient of the lens material is α, then the approximate formula for arc length A″B″ is as follows: become.

A″B″AB・(1−αt) For the reasons mentioned above, if a plastic lens is fixed in the lens frame using the conventional method, the radius of curvature changes due to temperature changes, and the radius of curvature changes at high temperatures. is small and increases at low temperatures. Therefore, the focus position deviates from that at room temperature, leading to worsening of various aberrations.

The example of Utility Model Application No. 55-138606 shown in FIG. 1E has two lenses 11,
An alignment member 14 is inserted between the centering members 12 and attached to the lens barrel 13, and held by a retaining ring 15.

This only reduces the friction between the two lenses 11 and 12, and the outer diameter of the lens is regulated by the lens barrel 13 or the retainer ring 15, which is the same as in the previous example, and it is not affected by temperature changes. This results in a change in the radius of curvature of the plastic lens.

As another known example, in the lens barrel described in Utility Model Application No. 49-11740, the lens holding ring presses the outer peripheral part of the lens via an O-ring, and the objective is to reduce the influence of manufacturing tolerances of the holding ring. do. The lenses in this case are not limited to plastic lenses, and are mainly intended to be ordinary glass lenses. In the case of plastic cleansing, there are no regulations when the temperature reaches low temperatures, but
When the temperature is high, the gap between the lens barrel and the outer circumference of the lens disappears, and the radius of curvature changes.

Furthermore, in this configuration, since the surface that the O-ring contacts is the slope of the lens, tightening of the retainer ring causes distortion torque to act on the plastic lens, resulting in a tendency for the radius of curvature of the lens to decrease. There is therefore a significant negative effect when the temperature rises.

SUMMARY OF THE INVENTION An object of the present invention is to provide a holding mechanism for a plastic lens which does not have the above-mentioned drawbacks and whose predetermined shape changes significantly when the temperature changes and which maintains the performance of the lens by fixing it to a lens frame.

Another object of the present invention is to provide a plastic lens holding mechanism that does not require additional adjustment devices such as a focus correction device within the practical maximum and minimum temperature range.

A holding mechanism for a plastic lens according to the present invention to achieve the above-mentioned object is such that, in the above-mentioned holding mechanism, a protrusion is formed on the extension line of the lens curvature on the holding ring side of the lens, and the plastic lens is pressed through the protrusion. It is composed of

With the above-described structure, the lens can freely slide relative to the barrel portion and the presser ring with a low coefficient of friction when the operating temperature changes. Therefore, no energy accumulation occurs that changes the radius of curvature when the temperature changes, and changes in the lens shape are extremely small. Therefore, the deviation of the focus position is also within a practically acceptable range, and there is no need for a correction device. Therefore, within the practical temperature range, plastic lenses can be designed exactly like glass lenses.

The protrusions may be a plurality of hemispherical protrusions arranged evenly as required, or may be elongated rod-shaped or arc-shaped protrusions with a semicircular cross section.

Embodiments and drawings illustrating the present invention will be described. Similar parts or components are indicated by the same reference numerals in the following figures.

2A and 2B show a first embodiment of the present invention,
A barrel part 22 and a fitting part 23 are formed on a metal lens frame 21 to engage a plastic lens 24 according to the present invention. A retaining ring 26 is screwed into an internal thread 25 formed on the lens frame 21 to hold the lens 24 in a predetermined position.

According to the present invention, the protrusion 27 is formed on the extension line of the lens curvature on the holding ring side of the lens 24. In the example shown in FIG. 2B, the projections 27 have height dimensions along the optical axis direction, with their axes aligned in the normal direction on the slope of the lens surface, and arranged at equal intervals on a circumference centered on the optical axis. be a plurality of substantially hemispherical protrusions with the same diameter. The lens-side surface 28 of the holding ring 26 is an annular surface perpendicular to the optical axis.

With the above-described configuration, the lens 24 is attached to the presser ring 26.
The surface 28 is brought into contact with the tops of the plurality of protrusions 27 on the hemisphere over a minute area, and slides with low frictional resistance during relative thermal expansion and contraction. Presser ring 2
The surface 28 of the lens frame 21 is parallel to the barrel portion 22 of the lens frame 21, and resistance does not increase or decrease during relative sliding of the lens. Therefore, upon relative expansion and contraction due to temperature changes, the lens 24 is free to move radially, and therefore no energy buildup occurs that would cause a change in the lens radius of curvature. Fitting portion 23 of lens frame 21
The inner diameter of the lens is such that the outer circumferential surface of the lens does not come into contact with the inner surface of the fitting portion until a predetermined maximum practical temperature, for example, approximately 45° C. is reached. Therefore, in the practical temperature range, the change in the radius of curvature of the lens is extremely small, and the resulting deviation in focus is within a predetermined tolerance range, eliminating the need for a temperature correction device for focus.

3A and 3B show an example in which a protrusion 31 is formed on the lens also on the side of the lens frame barrel attachment portion 22. Since the contact between the lens and the barrel portion is not a plane-to-plane contact but a very small area contact at the top of the hemispherical protrusion 31, the frictional resistance experienced by the lens is further reduced.

By adopting the holding mechanism of the plastic lens of the present invention, the design temperature change range (e.g. -23℃~
The change in the radius of curvature of the plastic lens at temperatures between
It was 3 to 1/10.

Because the change in the radius of curvature is small, the change in the air distance between adjacent lenses is also very small, and the movement of focus due to temperature changes is also very small, 1/3 to 1/3 of that of conventional lenses.
1/4, and there is no longer a need for a correction device for temperature changes in practice. For this reason, it has become possible to treat plastic lenses in exactly the same way as glass lenses in the practical temperature range.

[Brief explanation of the drawing]

1A to 1E show the known configuration, FIG. 1A is a partial sectional view showing a part of the lens frame and the lens holding mechanism, FIG. 1B is an enlarged view of part B in FIG. 1A,
FIG. 1C is a diagram showing the deformation of the lens due to an increase in temperature, FIG. 1D is a diagram showing the deformation of the lens due to a decrease in temperature, FIG. 1E is a partial sectional view showing another known configuration, and FIG. 2A is a diagram showing the deformation of the lens due to a decrease in temperature. Partial sectional view of the lens holding mechanism using the lens according to the first embodiment, Part 2B
The figure is an end view of the lens in the direction of the arrow in Figure 2A;
Figure A is a sectional view showing a modification of the lens in Figure 2A;
FIG. 3B is a right end view of the lens of FIG. 3A.

Claims (1)

[Scope of Claims] 1. In a lens holding mechanism that holds a plastic lens between a lens barrel mounting surface of a metal lens frame and a presser ring, the lens curvature is located on an extension line of the lens curvature on the presser ring side of the lens. protrusions having axes in the normal direction, spaced apart from each other on a circumference centered on the optical axis, and having the same height dimension along the optical axis, the tops of which are approximately hemispherical or semicircular in cross section. A lens frame having a lens fitting part that forms a gap up to the highest practical temperature between the lens and the outer peripheral surface of the lens, and a holding ring having a lens pressing surface parallel to the lens barrel mounting surface. A lens holding mechanism, characterized in that the protruding portion of the lens is slidably pressed by a pressing surface of a holding ring.