About the, Nikkor, Ed-series – Nikon NIKKOR ED 1200mm f-11 IF User Manual
Page 13: About the nikkor ed-series
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Accessories
Slip-on leather front lens cap
122mm screw-in filters
Rear lens cap LF-1
Teleconverter TC-200
Built-in 39mm screw-in filter L37C
Teleconverter TC-300
Gelatine slip-in filter holder
Teleconverter TC-14
Other 39mm screw-in filters
Aluminum Trunk CT-1203
ABOUT THE
NIKKOR
ED-SERIES
Correction
of
chromatic
aberration
in
camera
lenses
has
been
limited, for the most part, to the use of techniques which bring
two wavelengths of light, normally blue and red, to a common
focus.
Although
known
as
“achromatic,”
lenses
employing
these
designs
exhibit
a
certain
amount
of
undesirable
residual
dispersion
(called
the
“secondary
spectrum”)
which
limits
image
contrast
and
sharpness,
particularly
at
full
aperture.
Telephoto
lenses are most prone to the ill effects of chromatic aberration,
since secondary spectrum increases with focal length.
The
Nikkor
ED-series
consists
of
telephoto
and
super-telephoto
lenses
fitted
with
elements
made
of
a
Nippon-Kogaku-developed
special
optical
glass
called
Extra-low
Dispersion
(ED)
glass.
Although the optical characteristics of this new glass are similar
to
those of calcium-fluorite crystal, ED glass possesses a more
constant refractive index over a wide range of temperatures and
will, therefore, cause less of a focus shift. Also, ED glass is much
harder and more resistant to scratches, enabling its use for front
and
rear
lens
elements
to
obtain
optimum
correction
of
chro
matic aberration over the widest possible wavelength range. Some
lenses within the ED-series, such as this Nikkor ED 1200mm f/11
IF,
have
been
so
fully
corrected
that
image
sharpness
extends
uniformly to the infrared region; for these lenses, corrective re
focusing
for
infrared
exposures
is
unnecessary.
The
remaining
lenses have been built exceptionally compact due to the use of
ED glass elements; for these lenses, however, corrective refocus
ing
for
infrared
photography
is
necessary.
Regardless
of
which
type,
ED-series
lenses
offer
exceptional
sharpness
and
full
contrast
for
the
most
precise
photography
under
the
widest
conditions.
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