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Fujinon Precision Focus System
Focusing one step ahead
With HDTV shooting even experienced cameramen
often have difficulty in finding optimum focus and in
maintaining the sharpest focus on moving objects.
often have difficulty in finding optimum focus and in
maintaining the sharpest focus on moving objects.
The higher the resolution of the camera CCD the
smaller the individual pixels are, and therefore the
acceptable circle of confusion also becomes smaller.
Thus the depth of field is much smaller in HD than
when using SD cameras. This becomes even more
critical when long telephoto lenses are being used.
For conventional SD production the resolution of the
viewfinder is usually sufficient but in HD production
it is often not possible to determine optimum focus,
especially in adverse lighting conditions.
smaller the individual pixels are, and therefore the
acceptable circle of confusion also becomes smaller.
Thus the depth of field is much smaller in HD than
when using SD cameras. This becomes even more
critical when long telephoto lenses are being used.
For conventional SD production the resolution of the
viewfinder is usually sufficient but in HD production
it is often not possible to determine optimum focus,
especially in adverse lighting conditions.
The idea of the Precision Focus System
Fujinon, in close cooperation with NHK (Japan Broad-
cast Corporation), has developed a unique system,
which was introduced under the name of Precision
Focus System.
cast Corporation), has developed a unique system,
which was introduced under the name of Precision
Focus System.
The development was based on the following idea:
when the distance to an object is correctly focused,
the image contrast on a CCD sensor will be very high.
At the same time, if the contrast is also sampled in front
of and behind the CCD along the optical axis (see dra-
wing: sample points "A" and "B") it would be at a lower
Ievel than on the CCD but of the same value at each
sample point. lf the focus were incorrectly adjusted then
the contrast measured at the sample points would not
be equal. Thus it is possible not only to find the sharpest
focus position but also the direction of any necessary
adjustment required when focus is not sharp.
when the distance to an object is correctly focused,
the image contrast on a CCD sensor will be very high.
At the same time, if the contrast is also sampled in front
of and behind the CCD along the optical axis (see dra-
wing: sample points "A" and "B") it would be at a lower
Ievel than on the CCD but of the same value at each
sample point. lf the focus were incorrectly adjusted then
the contrast measured at the sample points would not
be equal. Thus it is possible not only to find the sharpest
focus position but also the direction of any necessary
adjustment required when focus is not sharp.
Fujinon designed and built the solution – mounting a
partly transparent mirror inside the lens, which directs a
small percentage of the image to the Precision Focus
System. This is a prism, which splits the light to reach
two additional CCDs. The CCDs are then used for
contrast measurement. ln the Precision Focus System
(please see diagram), the optical path from the mirror to
CCD "A" is shorter and the distance to CCD "B" Ionger
than the path from the mirror to the camera CCDs.
partly transparent mirror inside the lens, which directs a
small percentage of the image to the Precision Focus
System. This is a prism, which splits the light to reach
two additional CCDs. The CCDs are then used for
contrast measurement. ln the Precision Focus System
(please see diagram), the optical path from the mirror to
CCD "A" is shorter and the distance to CCD "B" Ionger
than the path from the mirror to the camera CCDs.
lf the subject is too far away, the value from CCD "A"
is higher than from CCD "B". lf the subject is too close
then the opposite is true. lt is precisely focused when
both signals are equal.
Fujinon. To see more is to know more.
is higher than from CCD "B". lf the subject is too close
then the opposite is true. lt is precisely focused when
both signals are equal.
Fujinon. To see more is to know more.
www.fujifilm.eu/fujinon