Focus adjustment

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A focus adjustment is understood to mean the following fact:

With color picture tubes , the focus of the lines is adjusted in order to obtain a sharp and high-contrast television picture . The focus grid is used for this .

The focus is set on the third vertical line at the height of the center line, because this is where the defocusing is greatest. If the grid is focused (brought into focus) at this point, then the defocusing becomes less and less towards the center of the screen. This gives a uniformly focused (sharp) television picture.