JPH04341Y2 - - Google Patents

Description

[Detailed description of the invention] [Field of industrial application] The present invention relates to the amount of transmitted light of a photographic lens that has an iris diaphragm and a mirror for extracting a part of the transmitted light flux to the outside of the lens barrel near the iris diaphragm. The present invention relates to an adjusting device, and more particularly to a transmitted light amount adjusting device that has a larger transmitted light amount adjustment range than a general iris diaphragm.

[Prior art]

In recent years, image pickup tubes incorporated into video cameras and the like have become highly sensitive, and a photographing lens attached to the tube is required to have a wide adjustment range for the amount of transmitted light.

On the other hand, the iris diaphragm is the most widely used conventional device for adjusting the amount of transmitted light in a photographic lens. However, the adjustment range of transmitted light amount of this iris diaphragm is limited to
The adjustment range was about 250 times, which caused the problem that the adjustment range was too narrow.

Another example of adjusting the amount of transmitted light of a conventional photographic lens is that the photographer inserts and removes a neutral density filter on the optical axis depending on the brightness of the subject at that time, and adjusts the adjustment range of the amount of transmitted light using the iris diaphragm. It is known to shift the value by several steps. However, inserting and removing the neutral density filter on the optical axis is troublesome, and is particularly undesirable for amateurs.

As yet another example of a conventional photographic lens transmission light amount adjusting device, one that combines a so-called star filter and an iris diaphragm is known. The star filter is 100% transparent at the periphery, the transmittance decreases stepwise or gradually toward the center, and the center is star-shaped and has the lowest constant transmittance, The dimensions are determined so that all the light beams transmitted through the iris diaphragm having the minimum aperture value pass through the star-shaped portion. However, the manufacturing cost of a filter with partially different transmittances is high, and the intermediate transmittance part forming an annular band in the middle only affects the middle part of the transmitted light amount adjustment range. Doesn't help with expansion.

[Purpose of invention]

The present invention was devised in view of the above-mentioned problems with conventional photographic lens transmitting light amount adjustment devices, and provides a transmitted light amount adjusting device that has a simple structure, is low in cost, and can continuously adjust the amount of transmitted light over a wide range. The purpose is to

[Structure of the idea]

The present invention has the following structural features to achieve the above object. That is, the present invention provides a photographic lens having an iris diaphragm and a mirror near the iris diaphragm for extracting a part of the transmitted light flux to the outside of the lens barrel, which has an outer shape different from the iris diaphragm aperture, and has at least A plastic neutral filter having a substantially uniform transmittance and having a size that allows all the light beams transmitted through the iris diaphragm having the minimum aperture value to pass therethrough is attached to a mirror support member for supporting the mirror. This is a device for adjusting the amount of transmitted light for a photographic lens.

〔Example〕

Hereinafter, embodiments of the present invention will be described based on the drawings. As shown in FIG. 1, the photographing lens 1 includes a plurality of lenses 2 supported by a lens barrel 4, an iris diaphragm having aperture blades 6, an autofocus device (not shown), and a viewfinder (not shown). (not shown) has a first mirror 8 and a second mirror 10 for extracting a necessary luminous flux.

The first mirror 8 is supported by a support member 14 together with the filter 12, as shown in FIGS. 2 and 3. The support member 14 is approximately U-shaped, and has a filter 12 attached to a vertical surface portion 16 at the center, and a first mirror 8 attached to an inclined portion 18. The support member 14 has screw holes 20 at both ends for attaching it to the lens barrel 4.

The filter 12 is shown in three examples A, B, and C in FIG.
As shown, the transparent part 20 and the support part 22 are integrally molded from the same material. Now, assuming that the iris diaphragm can be adjusted from F1.4 to F22, the transparent part 20 is its inscribed circle 24 (shown by the dotted line in FIG. 4).
A regular triangle A, a star B, a regular pentagon C, or any other shape is used so that the diameter of the iris diaphragm is equal to the diameter of the iris diaphragm adjusted to F8. The built-in filter 12 is located very close to the diaphragm blades 6, so that the width of the light flux that passes through the transmission section 20 is approximately equal to the width of the light flux that passes through the iris diaphragm.

The material of the filter 12 is plastic, which has no wavelength selectivity, that is, is neutral.
Furthermore, in order to prevent the transmitted light from diffracting, pigments containing particles or black ink are not used, and dyes or the like are used to lower the transmittance. Further, the filter member 1 cannot be made of metal vapor-deposited material in order to prevent the occurrence of flare or ghost.

Next, the operation of the transmitted light amount adjusting device having the above structure will be explained based on FIG. 5. The horizontal axis of FIG. 5 shows the aperture value of the iris diaphragm, and the vertical axis shows the amount of transmitted light of the present transmitted light amount adjustment device by the aperture value of the iris diaphragm in correspondence with the amount of transmitted light of the iris diaphragm. In other words, the vertical axis
F22 indicates that the amount of transmitted light of this transmitted light amount adjustment device is equal to the amount of transmitted light when the iris diaphragm is adjusted to F22 without the filter 12 and only an iris diaphragm.

In FIG. 5, a graph 30 shows the amount of light transmitted by the present device when the transmittance of the filter 12 is 12.5%, and a graph 22 shows the amount of light transmitted only through the iris diaphragm without the filter 12. It is assumed that the circumscribed circle 34 (indicated by a dashed line in FIG. 4) of the transmission portion 20 of the filter 12 is approximately equal to the diameter of the iris diaphragm when the iris diaphragm is at F4. In the graph 30, at F1.4 to F4 on the horizontal axis, a part of the light beam passing through the iris diaphragm is attenuated by the filter 12 and the support member 14, resulting in F(1.4+α) to F(5.6+β) on the vertical axis. , at F4 to F8 on the horizontal axis, a part of the light flux is attenuated by the filter 12 and becomes F(5.6+β) to F22 on the vertical axis, and F8 on the horizontal axis.
to 22, all of the luminous flux passes through filter 1.
It is attenuated by F22 to F64 on the vertical axis.

Therefore, the range of transmitted light amount adjustment by this device is practically F1.4 to 64, or approximately 2000 times, which is approximately F1.4 to 22, or approximately
This is much larger than 250 times.

In the above embodiment, the filter 12 is directly supported by the support member 14, but in another embodiment, the filter 12 is attached to the vertical surface of the first mirror 8 supported by the support member 14. You can.

[Effect of idea]

As described above, the present invention has a simple configuration in which a single filter member having a uniform transmittance is placed near the iris diaphragm by means of a support member for a mirror for a viewfinder, etc., so that the maximum aperture value and the substantial It has the effect of expanding the adjustment range of the amount of transmitted light by significantly attenuating the amount of transmitted light, and is extremely useful for highly sensitive photosensitive materials and image pickup tubes.
In particular, the above-mentioned filter can be manufactured by only one step of punching out a plastic filter material, which has a significant manufacturing advantage.

[Brief explanation of the drawing]

Fig. 1 is a cross-sectional view of the projection lens of this embodiment, Fig.
The figure is an enlarged front view of the filter support system, and Figure 3 is the second
4 is a front view of the filter, and FIG. 5 is a graph showing the amount of transmitted light in this embodiment. 1... Shooting lens, 2... Lens, 6... Aperture blade, 8... First mirror, 10... Second mirror,
12... Filter, 14... Support member, 20...
Transmissive part, 22... support part.

Claims (1)

[Scope of Claim for Utility Model Registration] A photographic lens having an iris diaphragm and a mirror near the iris diaphragm for extracting a part of the transmitted light flux to the outside of the lens barrel, which has an external shape different from the iris diaphragm aperture. , a plastic neutral filter having a substantially uniform transmittance and having a size that allows all the light beams transmitted through the iris diaphragm having at least the minimum aperture value to pass therethrough is attached to a mirror support member for supporting the mirror; A device for adjusting the amount of transmitted light of a photographic lens, which is characterized by: