JPS63106620A - Electronic image pickup optical system - Google Patents

Abstract

PURPOSE:To execute a direct photometry without increasing a back-focal distance, by forming as one body an optical path split member and a moire preventive filter, and decreasing the number of optical members placed between a photographic lens and an image pickup element. CONSTITUTION:As for a crystal low-pass filter 8, a half mirror surface 9 inclined by 45 deg. against the optical axis is provided in its inside and used as a half mirror prism for a direct photometry. Accordingly, a half mirror and the crystal low-pass filter 8 are formed as one body and the number of optical members decreases by one piece, comparing with a conventional example, therefore, a back-focal distance requested to a photographic lens 1 is shortened to about 24-26mm by an air reduced length. In this case, the crystal low-pass filter is formed by cutting a conventional crystal low-pass filter to 45 deg., and thereafter, polishing its cutting plane, performing half mirror coating, and thereafter, sticking it. In such a way, the direct photometry can be executed without increasing the back-focal distance requested to the photographic lens.

Description

[Detailed description of the invention] [Industrial application field] TECHNICAL FIELD The present invention relates to electronic imaging optical systems.

[Problems to be solved by conventional technology and invention] CC
In electronic imaging optical systems using solid-state imaging devices such as D, sampling of image intensity is discrete, so moiré tends to occur on images with frequencies near the sampling frequency.To prevent this moiré, Nowadays, crystal low-pass filters are often used.

In addition, in electronic still cameras, in addition to these low-pass filters, infrared cant filters and quick return mirrors to guide light to the viewfinder are often placed behind the photographic lens, giving the photographic lens a very long back focal length. For example, when considering a 273-inch solid-state image sensor, the back focus required for a standard lens focal length of about 130 is approximately 24 to 26 m in air equivalent length. This is a major obstacle when designing photographic lenses, and wide-angle lenses in particular end up with lens systems that have a very large number of lenses.

Furthermore, in electronic still cameras, there is a strong demand for the use of so-called direct photometry, which uses reflected light from the image plane, in the photometry system.However, in the case of solid-state image sensors such as COD, unlike silver-halide film, film Since the light that hits the camera is not scattered very much and is mostly reflected specularly, it is difficult to achieve a di-reflection + side light system in which the photometric element is placed off the optical axis like in silver halide cameras. Therefore, in order to perform direct photometry with an optical system using a solid-state image pickup device, it is necessary to arrange a prism including a half mirror, a pellicle mirror, or the like in the middle of the image pickup optical system. in this case,
The back focus required of the photographic lens will further increase, and the number of elements in the photographic lens will increase further.

Figure 3 shows the layout of a conventional direct photometry type electronic still camera imaging optical system that incorporates the above points. Filter 4
, crystal low-pass filter (generally several filters are bonded together to prevent moiré in multiple directions) 5 and C
Contains a CD protective glass 6. With this configuration, the back focus BF required for the photographic lens is extremely long, approximately 28 to 30 mm in air equivalent length.

SUMMARY OF THE INVENTION In view of the above problems, it is an object of the present invention to provide an electronic imaging optical system that enables direct photometry without increasing the bank focus required for a photographic lens.

[Means and effects for solving the problems] The electronic imaging optical system according to the present invention includes an optical path dividing member and an optical path splitting member that guide split light to a photoelectric conversion element arranged outside the imaging optical path, between the imaging lens and the imaging element. In an electronic imaging optical system, the optical path dividing member and the moire prevention filter are integrated, and the optical member is disposed between the photographing lens and the image sensor. This is a reduction in the number of .

〔Example〕

Hereinafter, the present invention will be described in detail based on the illustrated embodiment, with the same reference numerals assigned to the same members as in the above-mentioned conventional example.

FIG. 1 shows the configuration of a first embodiment of the present invention,
8 is a half mirror tilted at 45 degrees with respect to the optical axis inside.
This is a crystal low-pass filter that has a surface 9 and is used as a half mirror prism for direct photometry. According to this configuration, the half mirror and the crystal low-pass filter are integrated, and the number of optical members is reduced by one compared to the conventional example, so the back focus required for the photographic lens 1 is shortened to about 24 to 260 in terms of air equivalent length. Become.

Note that in this embodiment, the crystal low-pass filter 8 is
The crystal low-pass filter 5 shown in the figure is cut at 45 degrees, the cut surfaces are polished, a half mirror coat is applied, and the filters are bonded together.

As you can see from Figure 1, the crystal low-pass filter 8
If the interior of the is a half-mirror surface 9, the moire prevention effect will remain unchanged for transmitted light, but the moire prevention effect will not work well for reflected light, and the image may become blurred. There is no problem in doing so.

FIG. 2 shows the configuration of a second embodiment of the present invention,
10 is an infrared cant filter 11. This is a block in which a crystal low-pass filter 12 is bonded together, and a half mirror surface 14 tilted by 30° from the direction perpendicular to the optical axis is provided inside the block. The light reflected by the half mirror surface 14 is totally reflected by the object side surface of the lock 10, and then enters the photometric element. Furthermore, in this example, this block 1
0 also doubles as a protective glass for the COD, and the mirror that guides light toward the finder is also a half mirror 15. Therefore, the number of optical members is reduced by three compared to the conventional example, and the angle of the half mirror surface 14 is also 30 degrees from the direction perpendicular to the optical axis, which is smaller than in the first embodiment. The required back focus becomes even shorter, approximately 17 to 19 cages in terms of air length.

Incidentally, it goes without saying that the block does not have to be used also as the protective glass for the COD. Regarding the angle of the half mirror, in the above embodiments, angles of 45 degrees and 30 degrees were shown, but various variations can be considered by devising the shape of the block.

In addition, if the thickness of the half-mirror surface is not sufficient when placing it inside the crystal low-pass filter, it is better to form a block by bonding a glass member to the crystal low-pass filter and provide the half-mirror surface on this block. Furthermore, although the above description has been made regarding a direct photometry type optical system in an electronic still camera, the present invention is not limited to this, and for example, it is necessary to split the optical path to a light receiving element for white balance in a video camera. It goes without saying that the present invention can also be used in other optical systems that are equipped with a moiré prevention filter in the optical path and require optical path division, such as optical systems.

〔Effect of the invention〕

As described above, the electronic ↑ layer imaging optical system according to the present invention has the practically important advantage of being able to perform direct photometry without increasing the bank focus required of the photographing lens.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the configuration of a first embodiment of the electronic imaging optical system according to the present invention, FIG. 2 is a diagram showing the configuration of the second embodiment, and FIG.
The figure shows the configuration of a conventional example. 1...Photographing lens, 2...Quick return mirror, 4.11...Infrared cant filter, 6...
・・CCD protective glass, 7・・・・CCD, 8.12・
...Crystal low-pass filter, 9.14...Half mirror surface, 10...Block, 15...Half mirror 1BF...Back focus. 1-1Figure 1-2

Claims (1)

[Claims] In an electronic imaging optical system, an optical path dividing member that guides divided light to a photoelectric conversion element disposed outside the photographic optical path and a moire prevention filter that optically prevents moire are arranged between a photographic lens and an image sensor. An electronic imaging optical system characterized in that the optical path splitting member and the moire prevention filter are integrated.