38
1/2.3 inch sensor Full frame sensor
The image focused by the lens, shown by the red light paths is what
will
be “in sharp focus” on the sensor surface (red bar). The parts of
the
image which are farther away would be focused within the position
shown by the green bars and those parts nearer by the position within
the blue bars. The depth of these two focus zones is much smaller in the
case of the smaller lens element. Therefore for the smaller lens the
distance of this focus plane depth is nearer the sensor and thus appears
to be sharper than the same image focal position with the larger lens.
The physics definition refers to this as the “circle of
confusion” and it is
this which determines the DOF, or apparent depth of sharpness of the
respective images. The “quality” of this out of focus area is sometimes
called “bokeh” or the Japanese for confusion
Focus within the green
zone
Focus at Sensor plain
Depth of Field and Focus Zones
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