JPH0146041B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is applicable to optical equipment such as television cameras.
This relates to a focus adjustment method using TTL photometry.

Conventionally, this type of focus adjustment device has been disclosed, for example, in U.S. Patent No. 4185191 and Nippon Photo Industry Publishing Co., Ltd.'s Photo Industry Special Edition ``Modern Camera and Lens Technology'' (January 1957).
As already explained in considerable detail in pages 107 to 110 of the issue (published on May 20th), light from the subject is guided to an imaging lens, and a focus detection element consisting of a pair of photoelectric conversion elements is used. The subject is captured as two image patterns, at least one of the image patterns is displaced (shifted), the maximum phase shift between the image patterns within the displacement operation range is detected as a day focus amount, and the image pattern is shifted. - A method of adjusting the focus according to the focus amount is known.

However, in the above-mentioned focus adjustment device, there is no problem if the two image patterns α and β are in the pattern state as shown in the attached first drawing, but there is no problem as shown in the attached second drawing a. When trying to adjust the focus on a subject with a monotonous contrast, in this case, two image patterns α and β are created.
As shown in Fig. 2, image patterns α and β, so-called high-frequency patterns, are captured, which have approximately the same contrast ratio and several approximately identical shapes are formed on the same pattern. Therefore, in any of the displacement amounts e ₁ , e ₂ , e ₃ corresponding to the displacement operation range E of the image pattern β, the phase shift of the image patterns α and β becomes almost zero, and a focusing signal can be obtained. . For this reason, depending on which displacement amount is captured, the amount of defocus will vary depending on the phase shift at that time, resulting in a problem that the focusing device may malfunction. For example, in the case of a video camera, in particular, as the zoom state is made wide by the zoom operation of the zoom lens attached to the camera, focus detection is detected by each photoelectric conversion element of the focus detection element. As the area expands and the photoelectric conversion element captures the average contrast in the focus detection area and outputs it as an output signal, the amount of output change between the photoelectric conversion elements becomes monotonous, resulting in the high frequency pattern described above. In addition, the phase shift of the image patterns α and β also tends to become smaller in correspondence with the focal length of the zoom lens that is changed by the zoom operation, and malfunctions in focus detection are likely to occur. It was a lot.

The present invention has been made in view of the above, and is a focus adjustment method using a focus detection method similar to the above,
The focal length of a photographing lens such as a zoom lens attached to an optical device is detected, and the displacement operation range of the image pattern at that time can be variably set according to the focal length, so that at least the above-mentioned high frequency pattern is generated. The purpose of the present invention is to provide a focus adjustment method that can minimize malfunctions on the wide-angle side, which are easy to occur.

Hereinafter, the present invention will be explained in further detail based on an embodiment shown in the attached third drawing.

In the figure, L is a photographic lens such as a zoom lens,
Consists of L ₁ a focal lens group, L ₂ beam splitter, L ₃ master lens group,
Further, f _L is the focal length of the photographing lens L, and N is a zoom ring that supports a zoom lens group such as the zoom lens, and is provided in a correlation with the focal length f _L of the photographic lens L. This is focal length information. M is a mirror, Q is an imaging lens (imaging lens group), and K is a focus detection element, which is composed of a pair of photoelectric conversion element groups A and B, and the focus detection element K is controlled by the beam splitter _L2. If a part of the light from the subject (for example, a cold filter is used as a reflector of a beam splitter to mainly utilize the infrared light component), the problem of light intensity reduction to the imaging device can be solved. ), and the object is captured by the imaging lens Q as two image patterns α and β. I is a focus detection control unit which receives the output signals of the image patterns α and β captured by the focus detection element K, receives the signal of the focal length information N, and performs a displacement operation according to the focal length information N. The amount of displacement in the range E is variably set, for example, e ₁ in wide mode and e ₃ in tele mode, and the image patterns α and β are set within the displacement operation range E. At least one of the image patterns α and β is displaced, and the day focus amount Δp of the subject at that time is detected from the phase shift between the two image patterns α and β, and the a-focal lens L of the photographing lens L is adjusted according to the day focus amount Δp. ₁ or an imaging device (Z: for example, an imaging tube, a CCD,
Solid-state imaging devices such as BBD, MOS, and CID)
The focus is adjusted by driving and controlling at least one of the two in an appropriate direction.

That is, according to the focal length information N of the photographic lens L, the displacement operation range E of the image pattern is determined according to the focal length f _L of the photographic lens L, and the defocus amount Δp determined from the maximum phase shift at that time.
is set, and the microcomputer of the focus detection control unit I is controlled so as not to perform any further displacement operation, and the object of the pattern having the same level of contrast in the high frequency pattern existing outside the displacement operation range E is controlled. This was done so that there was no need to compare parts.

As described above, in the focus adjustment method according to the present invention, since the image pattern is not displaced beyond the maximum phase shift set based on the optical characteristics of the photographic lens, even if a high frequency pattern is generated, There is no need to compare high-frequency patterns outside the displacement operation range, and this has the remarkable effect of drastically reducing focus adjustment errors, especially on the wide-angle side, compared to the conventional method.

[Brief explanation of drawings]

Figure 1 shows a general image pattern captured under normal conditions, Figure 2 a shows a subject with monotonous contrast, and Figure 2 b shows the image pattern at that time.
FIG. 3 shows an embodiment of the focus adjustment method according to the present invention. In the diagram, L: Photographing lens, f _L : Focal length, L ₁
...A focal lens group, L ₂ ...Beam splitter, L ₃ ...Master lens group, N...
Focal length information, M...mirror, Q...imaging lens (imaging lens group), K...focus detection element, A/B...
...Pair of photoelectric conversion element groups, I...Focus detection control section, Z...Imaging device, α, β...Image pattern, E...Displacement operation range, _e1 , _e2 , _e3 ...Displacement amount.

Claims (1)

[Scope of Claims] 1. A part of the light of the object passing through the afocal lens group L1 is guided to the imaging lens Q, and the light of the object is detected by a focus detection element K consisting of a pair of photoelectric conversion element groups A and B. is captured as two image patterns α and β, and by displacing at least one of the image patterns α and β, the maximum phase shift between the image patterns α and β within the displacement operation is determined as the defocus amount. In a focusing device that detects the day focus as Δp and adjusts the focus according to the day focus Δp, the image pattern α is determined by the focal length f _L of the photographing lens L that is varied by the a-focal lens group L1. , β is set in advance, and the day focus amount is set within this maximum phase shift range.