Instructions
Table Of Contents
4
Main Characteristics
• New Focus Adjusting Device: Rear
Group
Focusing System
The
focusing adjustment is,
in
general, per-
formed by drawing
out
the
whole lens con-
struction. However, this lens has
adopted
the
focusing system which relies
on
the
rear group
of
the
lens,
in
which
one
part
of
the
rear lens
group moves while
the
front
lens group and
another
part
of
the
rear lens group remain
fixed. This rear group focusing system allows
the
heavy, large apertu re,
front
lens group
to
be firmly fixed
to
the
mount,
and allows for
focusing by moving
one
part
of
the
light,
small aperture, rear lens group.
As
a result,
operation
of
this lens has been
further
im-
proved because
of
the
reduced size
of
the
lens
barrel and simplified mechanism.
As
the
over-
all
length
of
the
lens does
not
change and a
minimum subject distance
is
as
short
as 4m
close-up shorts
of
a face can be
obtained
which will entirely
fill
the
picture frame
if
the
camera
is
held vertically_ This lens was
carefully designed
to
compensate for aberra-
tion and for high performance.
• Function Focusing Adjustment: Vari-pitch
Focusing Mechanism
In
the
conventional helicoid system,
as
the
protrusion
of
the
lens
is
determined according
to
the
rotation angle,
the
intervals between
the
distance scales become smaller when
focusing
is
required for distant subjects.
Another
drawback
of
the
helicoid
is
that,
since
the
depth
of
the
field
is
shallow, even
a slight error
of
the
focusing adjustment
leads
to
a blurred image. But,
the
FD400mm
uses a cam mechanism for
the
adjustment
of
the
lens. Hence,
the
adjustment
speed changes
according
to
the
curve
of
the
cam
in
order
to
allow enough space between
the
distance
scales
of
greater
than
15m_
This lens makes
finer focusing easier
as
it increases
the
graduation
in
the
focusing mechanism so
the
correct
focus can easily be identified and
the
possibility
of
distance adjustment errors
is
greatly reduced.
• Hand-Held Shooting
With
the
adoption
of
this new system, opera-
tion
is
greatly improved and hand-held shoot-
ing has become possible, because
the
lens
is
lightweight and well balanced. Of course,
stabilized hand-held shooting
is
obtained
when using
the
tripod
mount
.
• Excellent Optical Performance
Because
of
a well balanced design and pro-
perly adopted mechanism established through
the
use
of
the
fixed
part
of
the
rear lens
group, this lens has reduced secondary chro-
matic aberration
to
a minimum. It promises a
sharp picture image
in
every corner of
the
film.