Apparatus for and method of measuring focus

Details Apparatus for and method of measuring focus Apparatus for and method of measuring focus

1997-08-28

2000-06-06

Peng, John K.

Television

Video display

Cathode-ray tube

348380, 348745, 348189, 348180, 348178, 315382, 313382, H04N 326

Patent

active

06072546&

ABSTRACT:
A correct estimation of a focussed condition of the cathode ray tube can be performed. A predetermined image (14) is displayed at a predetermined position on a screen of a cathode ray tube. A focussing voltage of the cathode ray tube is varied in a condition that a distance from a reference position to a predetermined position in the image is detected. When the changing state of the detected distance is displayed on a predetermined display means (11a), an optical low pass filter is arranged in the optical system such as the incident part of a sensor (15) or the like. From an output of the sensor (15), a condition is determined as the just-focussed condition, the under-focussed condition or the over-focussed condition and the beam spot diameter is calculated from the detected line width. On the basis of the decision of the under-focussed or the over-focussed condition and the calculated value of the beam spot diameter, a focus quantitative value is obtained.

REFERENCES:
patent: 4686429 (1987-08-01), Fendley
patent: 5083195 (1992-01-01), Evelin
patent: 5334911 (1994-08-01), Emmoto
patent: 5440339 (1995-08-01), Harrison et al.
patent: 5526043 (1996-06-01), Wen
patent: 5621521 (1997-04-01), Takahashi
patent: 5734423 (1998-03-01), Wakabayashi
patent: 5777441 (1998-07-01), Yoshida et al.
patent: 5801768 (1998-09-01), Sudo et al.

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