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3 Glossaire des termes utilisés avec les
objectifs sur le site Nikon Japon (en anglais)
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Glossary |
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The ideal image by lenses
(especially photographic lenses), must fulfill three key
conditions, namely, (1) all light from the point object must be
focused to a single point on the image plane (film), (2) when the
object plane is perpendicular to the optical axis, the image plane
must also be perpendicular, and (3) the object and the image (on
the film) must closely resemble each other. In reality, however,
light refraction by the lens causes a variety of defects in the
image, called aberration.
The five most common types in
aberration are SEIDEL's
five aberrations, which occur even with monochromatic
(single-wave length) light, and two types of chromatic
aberrations, which are caused by more than one frequency.
It is
impossible to eliminate them all, but in the lens design process,
they can be controlled and balanced to provide the best possible
result for that lens and application. This is handled by material
(glass) selection, shape and positioning.
It is a phenomenon in
which light rays from an off-axis point form images at different
positions along meridional and sagittal directions. Astigmatism
causes points to blur, degrading sharpness. The visible phenomenon
is a blurring of background and foreground (object points appear
as linear or oval-shaped images).
It can be reduced but not
eliminated by stopping down the lens.
Back focal distance,
meaning the distance (length) from the tip of the lens's furthest
rear surface to the film surface where the image is
focused.
Glue made from pine
resin.
This glue is used to paste several lenses together.
Other than balsam, there are silicon-type, epoxy-type, and
ultraviolet curable resin available these days.
A lens that resembles a
symmetrical negative-positive-negative unit system wideangle
lens.
It was designed by Dr. Ludwig BERTELE when he was at a
Wild-Heerbrugg(Swiss) , and is known with lenses such as
Biogon 38mm, 53mm,
75mm, and 90mm ultrawideangle
lens (all made in 1954), made by Zeiss (Germany) .
Chromatic
Aberration is different from SEIDEL's
five aberrations caused by monochromatic light, and can be
broadly grouped into two types.
The first is longitudinal
chromatic aberration, in which focal points vary with wavelength.
This type of aberration
causes color smearing and a loss of sharpness in the center of the
image. It can be controlled by stopping down the lens.
The
second type is lateral chromatic aberration, in which
maginification varies with wavelength. Lateral chromatic
aberration is also known as transverse chromatic aberration or
chromatic difference of magnification. This is also visible,
causing color smear and loss of sharpness for non-axial light. It
will not improve even if the lens is stopped down, and smear will
increase in monochromatic film is used. It can be reduced by the
optimal combination of convex and concave lenses, and is greatly
reduced by low-dispersion ED glass.
Photographic lens design begins with the
precise control of SEIDEL's
five aberrations and the two types of chromatic
aberration, a total of seven. Because the distance to the
object can change from infinite to extremely close, however, the
corrected aberration
at infinity becomes incorrect at finite distances. This is yet
another type of aberration,
and it especially appear in asymmetrical lenses (telephoto, retrofocus).
Floating
adjustment, inner focusing (IF) and rear focusing (RF) techniques
were developed to minimize it.
Even when spherical
aberration has been corrected, light flux from objects apart
from the optical axis can cause coma. The visible phenomenon is a
point image on the picture trailing toward the exterior or the
center of the image, like a comet, which is where the name comes
from. Coma spreading radially from the optical axis forms a
teardrop-shaped flare, usually called a meridional coma flare. A
sagittal coma flare occurs concentrically, often for flying birds,
forming a diamond-shaped flare.
Coma can be reduced by stopping
down the lens.
Unlike spherical
aberration, coma
or astigmatism,
shows points as points, but the focal points do not match across
the image center and periphery in image planes, so that the image
is gradually bent out of shape toward the edges. In a composition
where light rays cross perpendicularly, for example, the image
might be focused in the center but not at the edges, or
vice-versa.
A phenomenon in which straight lines are not
rendered perfectly straight in the picture.
Curvature of field
can be improved but not eliminated by stopping down the lens.
Distortion, unlike spherical
aberration, coma
or astigmatism,
shows points as points, but affects the shape of the image. There
are three visible types, namely
(1) Barrel: Image deformation
causes a rectangle to swell in the center, looking like a barrel
(the corners of the rectangle are greater than 90 degrees).
(2)
Pincushion: Image deformation causes the sides of a rectangle to
move inward, forming a pincushion or star shape (the corners of
the rectangle are less than 90 degrees).
(3) Combinations: Two
types can also be combines.
Distortion cannot be corrected by
stopping down the lens, but it can be improved by optical
combination of positive and negative lens elements.
The first fisheye lens
from Nikon was the 16mm f/8 Fisheye lens (picture angle: 180
degrees, equidistant projection, circular image), which was
released in 1938. Here are the fisheye lenses that was
released:
| Fisheye-Nikkor 16.3mm
f/8 |
180 degrees
(Equidistant Projection ;
Circular Image) |
5 elements in 4 groups |
1957 |
| Fisheye-Nikkor 8mm
f/8 |
180 degrees
(Equidistant Projection ;
Circular Image) |
5 elements in 4 groups |
1962 |
| Fisheye-NIKKOR 7.5mm
f/5.6 |
180 degrees
(Equidistant Projection,
Circular Image) |
9 elements in 6 groups |
1966 |
| OP
Fisheye-NIKKOR 10mm f/5.6 |
180 degrees
(Orthographic Projection ;
Circular Image) |
9 elements in 6 groups |
1968 |
| Fisheye-NIKKOR 6mm
f/5.6 |
220 degrees
(Equidistant Projection ;
Circular Image) |
9 elements in 6 groups |
1969 |
| Fisheye-NIKKOR 8mm
f/2.8 |
180 degrees
(Equidistant Projection ;
Circular Image) |
10 elements in 8 groups |
1970 |
| Fisheye-NIKKOR 6mm
f/2.8 |
220 degrees
(Equidistant Projection ;
Circular Image) |
12 elements in 9 groups |
1972 |
| Fisheye-NIKKOR 16mm
f/3.5 |
170 degrees (Full-Frame, fisheye
image) |
8 elements in 5 groups |
1973 |
| Fisheye-Nikkor 16mm
f/2.8 |
180 degrees
(Full-Frame Fisheye
Image) |
8 elements in 5 groups |
1993 |
| AF Fisheye Nikkor 16mm
f/2.8D |
180 degrees
(Full-Frame Fisheye
Image) |
8 elements in 5 groups |
1994 |
| R-UW AF Fisheye NIKKOR 13mm
f/2.8 |
170 degrees at underwater
(Full-Frame
Fisheye Image) |
8 elements in 5 groups |
1994 |
| "Fisheye Type 20mm
f/8" |
153 degrees
(Full-Frame Fisheye
Image) |
3 elements in 2 groups |
1995 |
Fisheye Converter FC-E8
(For
Nikon Digital Camera COOLPIX Series) |
183 degrees
(Equidistant Projection ;
Circular Image) |
5 elements in 4 groups |
1998 |
Of
these lenses, OP Fisheye-Nikkor 10mm f/5.6 was the first fisheye
lens to adopt the Orthographic Projection optics.
Orthographic
Projection lens projects the celestial image directly onto the
film. In the leaflet of a sales manual, which was distributed to
major distributor in 1969, it read:
"When a picture is taken with this orthographic
projection lens, the reflectance factor from the sky image can
be easily obtained.
For example, in order to measure the
brightness of the building district for a metropolitan project,
you take the picture of the sky image from the road. By
measuring the volume of the sky image portion, then that becomes
the brightness of the sky, and it can measure that area's the
sky factor in numbers...". This OP Fisheye-Nikkor
10mm f/5.6 is the world's first aspherical SLR lens.
Other than
these lenses, there was a lens called "SAP-230 degrees
Fisheye-NIKKOR" (6.2mm f/5.6 ; developed around 1968) which was
not released for the public. This lens was the world's first
"EquiSolidangle Projection" (the volume of the image and the
solidangle on the film surface are proportional) fisheye
lens.
This lens also uses aspherical lens for correct
projection.
| SAP-230 degrees
Fisheye-NIKKOR |
230 degrees
(EquiSolidangle Projection
; Circular Image) |
7 elements in 10 groups |
1968 |
It was built in 1933. It is a five-story
steel-framed concrete building with a basement.
It is well
known even from the pre-W.W.II period for its international-style
architecture, which is compared to that of Tokyo Central Post
Office (Marunouchi 2-chome, Chiyoda-ku, Tokyo).
The work of
the architect, YAMASHITA Toshiro, can be found at Roppongi 7-chome
in Minato-ku, Tokyo (Western-style houses with a rotary at public
area. The houses are rented and it belongs to Machida Douzoku
Corporation (1935)).
Here, the term "power" is used for
refraction.
The lens is
designed by the combination of the basic lens structure (the
arrangement of concave and convex lens, position of the aperture,
etc.) and the (refractive index of) optical lens. After that, it
makes a calculation by tracking (plotting) the ray emitted from
one point of the subject, which goes through the lens and form the
image.
The ray tracing calculation is tried out over and over
by changing the circumstances (for example, by changing size of
the penetrating angle of the ray emitted from the subject,
distance between the subject, the wavelength of the ray, size of
the aperture, etc.). It tries to achieve optimal answer from the
feedback received by adjusting the lens's refractive index and the
using different optical lenses.
Though the computer does
all the tracing calculation these days, it used to be a manual
calculator. And even before that, an abacus and logarithmic table
was used (and calculated only by hand before that).
There
are more ray tracing calculation needed for a zoom lens when
compared with single focal length.
It
is a lens which has the principal point behind the rear part of
the entire lens. The design is like the reverse of a telephoto
lens (thus called "retro"), and since the back
focus (back focal distance) can be obtained longer than the
focal length, it is used mostly for SLR wideangle
lens.
Compared to symmetrical wideangle lens, the brightness of
the edge of the image field is great, but the distortion
is bigger.
From the outside, the front lens element is large,
and when looking at the aperture blade from the rear of the lens,
the aperture blade appears larger when seen from the
front.
The five
monochromatic aberrations analyzed by SEIDEL in Germany, in 1856:
1) spherical
aberration, 2)coma,
3) astigmatism,
4) curvature
of field and 5) distortion.
It is a lens type
invented by Dr. Ludwig BERTELE, a famous designer at Zeiss of
Germany. It is regarded as basically a combination of the Ernostar
and Tessar lens types. Because it can be made with large
diameters, and little glass-air surfaces, this type of lens was
the subject of considerable R&D before coating technology
developed.
The Sonnar lenses used as standard large-diameter
products offer short barrel lengths due to telephoto lens type,
and less saggital coma
flare than Gauss lenses. The design method used to reduce aberration,
however, was quite complex, making them difficult to manufacture,
and the close-range
aberration fluctuation was large. Then technology is carried
on in 105 to 135 mm lenses for 35 mm SLR cameras.
Most lenses use
spherical surfaces (as opposed to aspherical surfaces), so that
light flux parallel to potical axis (imaged in the center of the
image area, basically) does not focus on a single point in the
focal plane (on the film). This is spherical aberration. It
appears a halo, blur and loss of sharpness.
It becomes more
common at high aperture lens, and can be reduced by stopping down
the lens.
It can also be reduced by the optimal combination of
positive and negative lenses.
The photographic lens
Barrel is cylindrical style, so that rays outside the optical axis
will be cut off, partially or completely, by the barrel or lens
edge. This is called vignetting. If you look in from the front of
the lens, and tilting the lens, you will be able to see the
blockage clearly. The aperture, with a polygonal shape, is visible
on all lenses except retrofocus
lenses and negative lenses (including zooms).
In retrofocus
lenses, the aperture widens as you tilt the lens (peripheral
image is relatively bright). In addition to reducing light
intensity at peripheral, vignetting is also closely related to out
focus image.
Born in
Hyogo-Ken, Japan(Nippon). Studied at University of Tokyo under
Professor OANA, Jun, and joined Nippon Kogaku K.K. (present Nikon
Corporation) in 1948.
He is one of the founders of Nikkor lens
for S-series and F-series.
He also designed Micro-Nikkor lens
(lens for precise duplication) and Ultramicro-Nikkor lens (lens
for high-precision exposure system, such as ICs and LSIs).
He
was a director and became an advisor until 1993.
He received
"Purple Ribbon Medal" from the Emperor in Spring1996. He died the
same year on October 5th.
The first
Xenotar-type lens, "Xenotar 80mm f/2.8", was
first released in 1954 as a medium-aperture (around f/2.8)
standard lens for medium-size film format cameras by a German
manufacturer, Schnider.
This lens is a modified version of a
Gauss-type lens (this lens was made after Gauss-type lens was
introduced).
The cemented lens at the rear is composed of just
one concave lens, therefore it performs well as a medium-aperture,
medium
angle-of-field lens.
There was also a lens called
"Biometar" which was released around the same
time by another German manufacturer, Carl Zeiss Jena.
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