JPS6079313A - Holding device of plastic lens - Google Patents

Abstract

PURPOSE:To reduce generation of a stress in a lens, which is caused by a variation of a temperature, and to prevent deterioration of an optical performance by interposing an elastic member between a plastic lens and a lens barrel. CONSTITUTION:When a temperature rises, since an expansion quantity of each plastic lens 1, 2 and 3 is larger than that of a lens barrel 6 and interval rings 4, 5, a distance between the lens barrel 6 and each lens 1, 2 and 3, and between a lens holder 7 and the lens 1 becomes narrower than that of the time of a normal temperature. By this variation, elastic members 8, 9 are compressed, but by these elastic members 8, 9, a stress applied to the outside diameter of the lenses 1, 2 and 3, and the optical axis direction can be suppressed to a small one, therefore, a deformation of a lens surface can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a lens assembly suitable for video cameras, still cameras, etc., and particularly relates to a holding device for a plastic lens when the lens is a plastic lens. It is something.

[Prior art]

Because the lens surface is easy to mold, has excellent impact resistance, is lightweight, and is inexpensive, plastic lenses have become popular in place of glass lenses, and are also used as constituent lenses in lens sets for video cameras, still cameras, etc. It has come to be used.

However, on the other hand, plastic lenses have a variety of advantages, but on the other hand, they undergo a large amount of deformation due to thermal expansion, and therefore, when exposed to high temperatures, they have the disadvantage that their initial optical performance deteriorates significantly even after returning to room temperature. be.

Figure 1 is a one-sided view showing an example of a conventional assembled lens consisting of plastic lenses.
In l, 1.2.3 is a plastic lens, 4.5
6 is a spacing ring, 6 is a lens barrel, 6α is a lens receiver, and 7 is a lens presser.

A spacing ring 4.5 is fitted into the i11 cylinder 6, and a collar portion of a plastic lens 1.2°3 is inserted between these spacing rings 4.5. The outer diameter of the plastic lens 1.2.3 is manufactured with a tolerance of 20 μm to 30 #m, and the lens is positioned in the radial direction by fitting into the inner diameter of the lens barrel 6.

On the other hand, the lens holding tool 7 tightens the plastic lenses 1 and 2.3 to the lens receiving part 6G via the N11 septum 4.5 with a load of 5 to 10 kg, thereby positioning the lenses in the optical axis direction. , which prevents the lens from tipping over.

By the way, if the camera is exposed to high temperatures (e.g. 80 degrees Celsius), the plastic lens will expand in the radial direction J.
tjD is ΔD-DXα×ΔT, where the diameter of the plastic lens is α, which is the coefficient of thermal expansion of the D1 plastic lens, and the temperature difference from room temperature (20°C) is ΔT°C.
...(11) In this formula (11), if the lens diameter is 20a1, the thermal expansion coefficient α of styrene resin, an acrylic resin commonly used for plastic lenses, is 57×10~10XIO/'C1 Temperature difference from room temperature, il
Since T is 60C, the plastic lens will expand 84 to 1004 m in the radial direction.

This thermal expansion occurs not only in the radial direction but also in all parts such as the lens surface and the optical axis direction of the lens. Of these, the change in the radius of curvature due to thermal expansion of the lens surface is not a problem because the dryness is compensated for in advance in the optical design, but thermal expansion in both the radial direction and the optical axis direction of the lens impairs optical performance. This is a contributing factor to the decline. In particular, when the lens barrel 6 is made of a metal such as aluminum whose coefficient of thermal expansion α is sufficiently smaller than that of a plastic lens, if the amount of thermal expansion of the plastic lens in the radial direction exceeds the above-mentioned official value (20 to 30 μm). , the plastic lens is restrained by the lens barrel, and as a result, stress is generated within the plastic lens, and this stress deforms the lens surface.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide a plastic lens holding device that eliminates the drawbacks of the prior art described above, reduces stress generation within a plastic lens caused by temperature fluctuations, and does not cause deterioration in optical performance.

[Summary of the invention]

In order to achieve this object, the present invention interposes an elastic member between the plastic lens and the lens barrel, and the elastic member provides pressure so as to absorb the stress generated within the plastic lens due to temperature fluctuations. The points are distinctive.

[Embodiments of the invention]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 2 is a cross-sectional view showing an embodiment of the assembled lens according to the present invention. FIG. 3 is a cross-sectional view taken along line A-5 in FIG. 2, and parts corresponding to those in FIG. There is.

In Fig. 2, 1, 2.3 are plastic lenses with flange parts made of acrylic resin, styrene resin, etc.;
4 and 5 are aluminum spacing rings, and 6 is a lens receiving part 6α.
7 is an aluminum lens holder, 8 is an annular elastic member made of silicone rubber, etc., and 9 is an annular elastic member made of fluororubber. .9 was cut into a desired length after extrusion and continuous vulcanization. Each plastic lens 1.2.3 and each spacing ring 4.5 have elastic members 8
is inserted into the lens barrel 6 through the lens receiving portion 6α of the lens barrel 6.
and a lens holder 7. The optically required lens position and lens spacing are based on the lens receiver 65, the thickness of the brim of each plastic lens 1.2.3, the distance between the rings 4.5, and the elastic member 9 and K. ℃
, is defined and maintained at a predetermined position within the mirror @6.

In this configuration, if the temperature now rises,
As mentioned above, since the amount of expansion of each plastic lens 1.2.3 is larger than that of the lens barrel 6 and the spacing ring 4.5, the space between the lens barrel 6 and each plastic lens 1.2.3, and the lens The distance between the presser 7 and the plastic lens 1 is 1, and the temperature is f.
) become narrower than at times. This fluctuation causes the elastic member 8.
9 is compressed, but the stress applied to the outer diameter and optical axis direction of the plastic lens 1.2.3 can be suppressed to a small level due to the elasticity Al14'8.9, so that the deformation of the lens surface of the plastic lens can be suppressed. It can be prevented.

Now, if the outer diameter of the plastic lens 1.2.3 (or the outer diameter of the collar if it has a collar) is D#II, then as a result of the experiment, the stress Prk applied to the outer diameter of the plastic lens is Prk.
It was found that until g/- is Pr<D15 (2), the amount of deformation of the lens surface is small (the change in spherical accuracy due to the laser interference part is within 5 interference fringes). . The stress exerted on the outer diameter part K of the plastic lens can be regarded as the stress generated in the elastic member 8, that is, the compressive stress caused by the elastic member 8 being compressed by the thermal expansion wind generated from equation 11 as described above. , it goes without saying that if the elastic member 8 is already compressed by stress in the initial (reference temperature) state, the above-mentioned compressive stress due to the temperature rise is added to this initial compressive stress. Although it is not easy to accurately measure compressive stress, especially when the elastic member 8 is thin, compressive stress can be easily measured because it is approximately proportional to the hardness or elastic modulus of the elastic member. As described above, by using the elastic member 8 whose generated compressive stress satisfies the above-mentioned formula (2), deformation of the lens surface of the plastic lens can be prevented.

Similarly, the plastic lens 1.2.3 has a spacing ring 4.5
Assuming that tm is the sum of the thicknesses of the parts sandwiched by
It was found that the amount of deformation of the lens surface was small until Ic9/t was Pz<2t (8). This stress pz can also be reduced in the same way as pr mentioned above, but since the stress in the optical axis direction also serves to support and fix each plastic lens 1, 2.3, if the stress is too small, If an impact force is applied to the assembled lens, the plastic lens may move and cause core scratches or fall, resulting in a deterioration of optical performance. Such a phenomenon also occurs when one camera is exposed to low temperatures and the amount of thermal contraction of the thickness of the plastic lens becomes larger than the thermal contraction wind of the lens barrel 6.

Therefore, the minimum necessary stress applied to the plastic lens exists at IYt and Te in the optical axis direction. This minimum stress is caused by the aforementioned T-fin (a plastic lens is sandwiched between spacing rings, etc.).

If all the constituent lenses of the lens set are plastic lenses, t15kg, tt
m'', and in the case of a lens assembly in which most of the constituent lenses are glass lenses and a small number of plastic lenses, t
/2~t kl / am". Therefore, when considered together with the limit value when exposed to high mK shown in equation (3), t15 < Pz (2t --- (4) To do this, it is necessary to remove the elastic member 9 during assembly at room temperature.
Within the range that satisfies equation (4) (approximately t Icy / +
It is necessary to apply a preload of "m").

- As an example, plastic lenses 1, 2, 3 (7)
In this example, the outer diameter is 29 mm and the thickness of the brim of each lens is 1.5 mm, the hardness is 80 according to JISK6301.
The elastic mi material 8 made of silicone rubber is made so that the inner diameter is slightly larger (approximately 30 μm) than the outer diameter of the lens brim, the wall thickness is 1.51111 mm, and the outer diameter is in contact with the inner surface of the lens barrel 6. None, and hardness 6 with a cross-sectional shape of 1# helical angle
The elastic member 9 is made of 0 fluororubber with a thickness of 0
．． When assembled and compressed to 7 IIm, even if this assembled lens is exposed to a temperature environment in the range of -20 to 80 degrees Celsius,
It was introduced that no deterioration in optical performance was observed and there was no problem in practical use.

It should be noted that the elastic member 8.9 has a compressive stress generated above (2).
), as long as it satisfies formula (4), there are no particular restrictions on the material, but care should be taken to ensure that it does not corrode or deteriorate the plastic lens. For example, it is possible to appropriately select from the material (7) used in the above example, chloroprene rubber, butyl rubber, urethane rubber, nitrile rubber, etc. Each of these rubbers can be carbon compounded, so there is a degree of freedom in selecting the material. is big.

FIG. 4 is a sectional view showing another embodiment of the present invention in which a glass lens and a plastic lens are used together as constituent lenses. In FIG. 4, 1° and 2′ are glass lenses, 3 is a plastic lens, 10 is an elastic layer, 11 is an elastic member, and 12 is a lens receiver screwed into the lens barrel 6. , others, ff1252IIC da 1
Corresponding parts (・) are given the same reference numerals and their explanation will be omitted.

In the case of this embodiment, it is the elastic layer 10 that absorbs the thermal expansion of the plastic lens 3 in the optical axis direction.

This elastic layer 10 is made by shot-plasting the processed surface of the spacer ring 5 made of metal grains such as aluminum or brass, and then applying a vulcanized adhesive such as chlorinated rubber or urethane to this processed surface and drying it. As shown in FIG. 5, an elastic layer 10 is formed at one end of the spacer ring 5.
It is integrally formed. In FIG. 5, the elastic layer 1
It is the thickness X that acts as an elastic member, and care must be taken that this portion satisfies the above-mentioned equation (4). Note that when the spacing ring is used in such a manner that it comes into contact with the spherical surfaces of the two plastic lenses, if the elastic layer 10 is formed at both ends of the spacing ring,
This is preferable because it does not damage the spherical surface of the lens during assembly. In this case, it goes without saying that the sum of the thicknesses of the elastic layers 10 at both ends acts as an elastic member.

Further, in the case of this embodiment, it is the elastic member 11 that absorbs the thermal expansion of the plastic lens 3 in the radial direction. As shown in FIG. 6, this elastic member 11 has a U-shaped cross-sectional shape that is open inward, and is obtained by compression molding pressure. Care must be taken to ensure that the elastic member 11 satisfies the equation (2) described above as a member that absorbs the thermal expansion of the plastic lens 3. FIG. and FIG. 8 is a sectional view taken along the line B--B in FIG. 7, where 12 is a plastic lens and 13 is a spacing ring.

There are 90 protrusions 14 around the plastic lens 12.
It is provided on 4 sides at every turn. On the other hand, the spacing ring 13 is provided with a concave portion 15 and a convex portion 16, and e417 is provided on the inner bottom of the concave portion 15 every 90 degrees [4 sides]. The plastic lens 12 has six grooves 17 in each protrusion 14 on the periphery.
It is held in the spacing ring 1.3 by fitting into the spacing ring 1.3. At this time, the gap C between the protrusion 14 and the groove 17 is set to be 10 μm or less, and this K prevents the plastic lens 12 from misaligning with respect to the spacing ring 13VC.

FIG. 9 is a sectional view of a lens assembly using the plastic lens 12 and the spacing ring 13, where 18 is a 1111
Sl 9 is another plastic lens. To incorporate these plastic lenses 12.19 into the mtllxs, insert the convex part 16' of the other spacing ring 13' that holds the plastic lens 19 into the four parts 15 of the spacer ring 13 that holds the plastic lens 12, and then Other time gA Bu 1
3° recess 15° and another protrusion 1 on the spacing ring 13'
6". In this way, the four parts and the convex part of one adjacent spacing ring sandwich the brim part of the plastic lens, so that each plastic lens has a length of m
Defined and held at a predetermined position within 1xs.

If a lens assembly having such a structure is now exposed to crystal wetting, the projections 14 will extend in the radial direction of each lens due to thermal expansion of each plastic lens 12 and 19. This extension of the protrusion 14 causes the protrusion 1
4 will slide within the groove 17, and no misalignment will occur, and the spacing ring 13 and plastic lens 12 will slide within the groove 17.
Plastic lens 1 is non-contact except for 14.
2 is not restrained not only by the lens barrel 18 but also by the spacer ring 13.

Similarly, the protrusion 14 extends in the optical axis direction due to thermal expansion of the plastic lens 12, but since the thickness of the protrusion 14 is usually between 1 and 31, the thermal expansion of the protrusion 14 The thickness is about 18 μm even for the three dragons.

Therefore, if the gap between the convex part 16' of the spacing ring 13' and the protruding part 14 is given in advance as 18 μm as indicated by IO, deformation of the lens surface can be prevented. Then, even if this gap is zero, it will not be a problem.

In this way, in this first example, the absorption of 1 tension P of the plastic lens is carried out by the protrusion 14 provided on the outer periphery of the plastic lens, and this protrusion 14 absorbs R'r.
Since the structure is designed to both center the lens during eA and prevent misalignment at high temperatures, the optical performance of the assembled lens at room temperature can be maintained even at high temperatures. The above is a brief explanation of thermal expansion at high temperatures, but the same applies to contraction at low temperatures.
Optical performance can be maintained by a similar effect.

Since the spacing ring 13 used in the above embodiment has a groove 17 provided at the inner bottom of the four parts 15, the groove 17 must be milled using an end mill, which is not good in productivity. Therefore, it is also possible to improve productivity by forming grooves 17 with a metal saw in the ring 13 at one interval, as shown in FIG. 10. However, in this case, the light incident on the lens assembly bends through the groove 17 and reaches the mirror ftJ18 shown in FIG.
It is necessary to apply anti-reflection treatment such as black painting to the inner peripheral wall of j+18.

FIG. 11 is a front view of a spacer ring and a plastic lens showing still another embodiment of the present invention, and in this figure,
Reference numeral 20 indicates a synthetic rubber adhesive, and the partial pressures corresponding to the 7th and 9th figures are designated by the same reference numerals, so that the explanation thereof will be omitted.

In the case of this embodiment, the Il#J septum 13 is
Using the same eAK processing as the actual case explained in the figure, each protrusion 14 provided around the plastic lens 12 is
After fitting into each groove 17 of the spacing ring 13, a synthetic rubber adhesive 2o is poured into the groove 17 to fix the protrusion 14 to the spacing ring 13. A plurality of plastic lenses 12 and spacing rings 13, which have been fixed in this way, are inserted into one lens barrel 18 as shown in FIG. 12 to assemble a lens assembly. The differences between this embodiment and the embodiments shown in FIGS. 7 to 9 described above are as follows.
Plastic lens 12.1 is formed by fitting the spacer rings together.
Since each plastic lens 12, 19 is independently fixed at each interval ml 3 and 1 go, instead of holding 9, the intervals ml 3 and 1 are fixed to each other, so that it is sufficient to simply press the intervals between the rings. Therefore, this embodiment has a particularly remarkable effect when the thickness of the protrusion 14 of the plastic lens is 5n or more and the amount of change in the protrusion 14 due to temperature changes becomes large. Since machining of fitting recesses and protrusions is not required, the rings 13 with one interval can be manufactured at low cost.

〔Effect of the invention〕

As explained above, one aspect of the present invention is that the structure is such that the thermal expansion of the plastic lens due to temperature fluctuations is absorbed by the elastic member, so that the stress generated within the plastic lens can be reduced, and therefore the optical performance can always be improved. It becomes possible to provide a lens assembly that does not deteriorate.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view showing an example of a conventional plastic lens holding device, FIG. 2 is a cross-sectional view showing an embodiment of the plastic lens holding device according to the present invention, and FIG. 3 is a line A-A in FIG. @ sectional view, FIG. 4 is a sectional view showing another embodiment of the plastic lens holding device according to the present invention, FIG. 5 is a perspective view of the spacing ring and elastic layer shown in FIG. 4, and FIG. FIG. 4 is a perspective view of the elastic member shown in FIG. 4, FIG. 7 is a front view showing still another embodiment of the plastic lens holding device according to the present invention, FIG. The figures are a sectional view of a lens assembly using the spacing ring shown in FIG. 7, FIG. 10 is a perspective view showing another embodiment of the spacing ring, and FIG. 11 is a further embodiment of the plastic lens holding device according to the present invention. A front view showing the embodiment, and FIG. 12 is a sectional view of a lens assembly using the spacer ring shown in FIG. 11. 1.2.3, 12.19... Plastic lens, 4.5.13... Spacing ring, 6, 18...
...lens barrel, 8.11.20...elastic member. f1 figure to L 72 town 13 figure 1'5 year old figure 4 figure O6 trouble 79 Roa 11 ship

Claims (1)

[Claims] In a lens set in which a plurality of lenses are each positioned within a lens barrel by spacer rings, and at least one of the lenses is a plastic lens, an elastic member is interposed between the lens barrel and the plastic lens. Characteristic plastic lens holding device.