Camplus Photography Equipment is one of China's leading distributor and manufacturer of photography equipment. We are forcusing on online retailing, business to business service and manufacturing. camplus.shop
http://stores.shop.ebay.com/camplus-shop
# Lens Accessories - Mount Adpator / Converter :
http://stores.shop.ebay.com/camplus-shop_For-EOS_W0QQ_fsubZ290091419QQ_sidZ654376679QQ_trksidZp4634Q2ec0Q2em322
-------------------
Tamron Learning Center - http://www.tamron-usa.com/lenses/learning_center/pro_learning_center_choosing.asp
Canon Lens
http://www.usa.canon.com/consumer/co
ntroller?act=MultiMiscPageAct&key=Lens_Advantage_Select&fcategoryid=140
Lens Chart:
http://www.usa.canon.com/app
/pdf/lens/Lens_Extender_chart_new.pdf
Most highly regarded among professional photographers, Canon L-series lenses are distinguished by a bold red
ring around the outer barrel. What makes them truly distinctive, however, is their remarkable optical
performance — the result of sophisticated Canon technologies, such as Ultra-low Dispersion UD glass, Fluorite
and Aspherical elements, and Super Spectra Multi Coating.
Designed for the Canon EOS 50D, 40D, all EOS Rebel and EOS Digital Rebel models with APS-C sized sensors
(with a 1.6x crop factor), Canon’s EF-S Lenses take advantage of the sensor’s smaller size, to deliver optimized
performance in compact, lightweight designs. The EF-S 17-85mm f/4-5.6 IS USM is a perfect example of this
technology. With a compact design, a 35mm equivalent range of 27-136mm, and Optical Image Stabilizer
technology, it’s a superlative walkaround Lens...possibly the only Lens you'll need to enjoy digital SLR
photography.
Macro Lenses — Canon’s Lens lineup has a number of options for true close-up and macro photography. With six
macro Lenses for precision, and three screw-on close-up Lenses for convenience, in addition to the Life-Size
Converter EF and two Extension Tubes, Canon's macro Lenses and close-up accessories can uncover detail that
is impossible for the unaided human eye to detect.
--------------
NIKKOR LENS
NOMENCLATURE:
http://www.nikonians.org/nikon/slr-lens.html
Nikon / Nikkor LENS TYPE CHARACTERISTICS:
Pre-AI Non-AI Manual Focus Nikon lenses made from 1959 and prior to 1977. Don't have a CPU. All Non-AI
lenses have a letter after the word Nikkor, to tell the number of elements in the optical formula. For example, in
the Nikkor-P 105mm f/2.5, the P stands for Penta, i.e. five elements.
Types: A (chrome filter ring), C (black filter ring) and K (rubber coating)
AI Manual Focus Nikon lenses, produced from 1977 until mid 80's, introduced Automatic Maximum Aperture
Indexing. A mechanism for meter coupling, that is, to inform the meter in the body what is the maximum
aperture of the mounted lens. With all black barrel, rubber focusing ring and multicoated elements. Don't have a
CPU chip.
AI-S Manual Focus Nikon lenses, introduced in 1982, with Aperture Indexing Shutter system for meter
coupling. Smallest aperture is orange (if not, then the lens is either AI or pre-AI). Most of these lenses have
extraordinary optics, like the legendary 105mm f/2.5, available in AI-S version. Don't have a CPU.
E Manual AI-S Nikon Series E lenses, made for the compact Nikon EM introduced in 1979, starting the
use of plastics. The 75-150mm f/3.5 Series E reached mythical stature. Don't have a CPU.
AI-P Manual AI-S Nikon lenses with a CPU that sends the lens information to the camera body. The latest is
the ultracompact Nikkor 45mm f/2.8 P "pancake", made to celebrate the FM3A and proving Nikon's loyalty not
only to film enthusiasts but also to manual body users.
F3AF Auto focus pioneering Nikon lenses introduced in 1983, exclusively for the F3AF.
AF Auto focus Nikon lenses introduced in 1986. When on Auto bodies, there is no need to use the
aperture ring in auto modes. AI-S lenses with a built-in CPU and screw motor for AF operation.
AF-D Introduced in 1992. AF Nikon lenses with a CPU that also relays distance information to the camera,
most useful for ultra-precise TTL flash. Among the first were the 35-70mm f/2.8D AF and 80-200mm f/2.8D ED
AF Nikkor.
AF-I Introduced in 1992. Nikon lenses with a coreless Integrated motor for faster AF in high-end telephoto
lenses. The first were the 300mm f/2.8 and the 600mm f/4, both D ED IF AF-I.
AF-S Introduced in 1996, Nikon AF-D lenses with a "Silent Wave" ultrasonic motor of their own, for fastest
AF operation. The first were the 300mm f/2.8, 500mm f/4 and 600mm f/4, all D ED IF AF-S Nikkor.
G Introduced in 2000. Nikon AF-D lenses without aperture ring. Need to be controlled through the body
dials of latest cameras. The first was the 70-300mm f/4-5.6G AF.
VR Introduced in 2000. Nikon lenses with a Vibration Reduction system allowing for crisp images handheld
at very slow shutter speeds. The first was the 80-400mm f/4-5.6D ED VR Zoom Nikkor.
DX Introduced in 2003. Nikon G lenses designed to just fill the frame of the DX format APS-C sensor size
used in Nikon D-Series SLR cameras. The first was the AF-S DX 12-24mm f/4G IF-ED Nikkor.
--------------------------------------------------------------------
Canon Lens Glossary:
http://www.usa.canon.com/consumer/controller?
act=GlossaryAct&fcategoryid=216
---------------
Aberration
The image formed by an ideal photographic lens would have the following characteristics:
1. A point would be formed as a point.
2. A plane (such as a wall) perpendicular to the optical axis would be formed as a plane.
3. The image formed by the lens would have the same shape as the subject.
Also, from the standpoint of image expression, a lens should exhibit true color reproduction. If only light rays
entering the lens close to the optical axis are used and the light is monochromatic (one specific wavelength), it
is possible to realize virtually ideal lens performance. With real photographic lenses, however, where a large
aperture is used to obtain sufficient brightness and the lens must converge light not only from near the optical
axis but from all areas of the image, it is extremely difficult to satisfy the above-mentioned ideal conditions due
to the existence of the following obstructive factors:
* Since most lenses are constructed solely of lens elements with spherical surfaces, light rays from a single
subject point are not formed in the image as a perfect point. (A problem unavoidable with spherical surfaces.)
* The focal point position differs for different types (i.e., different wavelengths) of light.
* There are many requirements related to changes in angle of view (especially with wide-angle, zoom and
telephoto lenses).
The general term used to describe the difference between an ideal image and the actual image affected by the
above factors is "aberration." Thus, to design a high-performance lens, aberration must be extremely small, with
the ultimate objective being to obtain an image as close as possible to the ideal image. Aberration can be
broadly divided into two classifications: chromatic aberrations, which occur due to differences in wavelength,
and monochromatic aberrations, which occur even for a single wavelength.
---------------
Chromatic aberration
When white light (light containing many colors uniformly mixed so that the eye does not sense any particular
color and thus perceives the light as white) such as sunlight is passed through a prism, a rainbow spectrum can
be observed. This phenomenon occurs because the prism's index of refraction (and rate of dispersion) varies
depending on the wavelength (short wavelengths are more strongly refracted than long wavelengths). While
most visible in a prism, this phenomenon also occurs in photographic lenses, and since it occurs at different
wavelengths is called chromatic aberration.
There are two types of chromatic aberration: "axial chromatic aberration," where the focal point position on the
optical axis varies according to the wavelength, and "chromatic difference of magnification," where the image
magnification in peripheral areas varies according to the wavelength. In actual photographs, axial chromatic
aberration appears as color blur or flare, and chromatic difference of magnification appears as color fringing
(where edges show color along their borders). Chromatic aberration in a photographic lens is corrected by
combining different types of optical glass having different refraction and dispersion characteristics. Since the
effect of chromatic aberration increases at longer focal lengths, precise chromatic aberration correction is
particularly important in super-telephoto lenses for good image sharpness.
Although there is a limit to the degree of correction possible with optical glass, significant performance
improvements can be achieved using man-made crystal such as fluorite or UD glass. Axial chromatic aberration is
also sometimes referred to as "longitudinal chromatic aberration" (since it occurs longitudinally with respect to
the optical axis), and chromatic difference of magnification can be referred to as "lateral chromatic aberration"
(since it occurs laterally with respect to the optical axis).
Note: While chromatic aberration is most noticeable when using color film, it affects black-and-white images as
well, appearing as a reduction in sharpness.
---------------
Circle of confusion
Since all lenses contain a certain amount of spherical aberration and astigmatism, they cannot perfectly
converge rays from a subject point to form a true image point (i.e., an infinitely small dot with zero area). In
other words, images are formed from a composite of dots (not points) having a certain area, or size. Since the
image becomes less sharp as the size of these dots increases, the dots are called "circles of confusion." Thus,
one way of indicating the quality of a lens is by the smallest dot it can form, or its "minimum circle of confusion."
The maximum allowable dot size in an image is called the "permissible circle of confusion."
--------------------------
Depth of field
The area in front of and behind a focused subject in which the photographed image appears sharp. In other
words, the depth of sharpness to the front of sharpness to the front and rear of the subject where image blur in
the film plane falls within the limits of the permissible circle of confusion. Depth of field varies according to the
lens' focal length, aperture value and shooting distance, so if these values are known, a rough estimate of the
depth of field can be calculated using the following formulas:
Front depth of field = d x F x a2 / (f2 + d x F x a)
Rear depth of field = d x F x a2 / (f2 - d x F x a)
f: focal length
F: F number
d: minimum circle of confusion diameter
a: subject distance (distance from 1st principal point to subject)
If the hyperfocal distance is known, the following formulas can also be used:
Near Point limiting = Hyperfocal distance X shooting distance
Hyperfocal distance + shooting distance
Far Point limiting = Hyperfocal distance X shooting distance
Hyperfocal distance – shooting distance
(Shooting distance: Distance from film plane to subject)
In general photography, depth of field is characterized by the following attributes:
1. Depth of field is deep at short focal lengths, shallow at long focal lengths.
2. Depth of field is deep at small apertures, shallow at large apertures.
3. Depth of field is deep at far shooting distances, shallow at close shooting distances.
4. Front depth of field is shallower than rear depth of field.
-------------------------------
Depth of focus
The area in front of and behind the focal plane in which the image can be photographed as a sharp image. Depth
of focus is the same on both sides of the image plane (film plane) and can be determined by multiplying the
minimum circle of confusion by the F number, regardless of the lens focal length. With modern autofocus SLR
cameras, focusing is performed by detecting the state of focus in the image plane (film plane) using a sensor
which is both optically equivalent (1:1 magnification) and positioned out of the film plane, and automatically
controlling the lens to bring the subject image within the depth of focus area.
------------------
Focal length
When parallel light rays enter the lens parallel to the optical axis, the distance along the optical axis from the
lens' second principal point (rear principal point) to the focal point is called the focal length. In simpler terms,
the focal length of a lens is the distance along the optical axis from the lens' second principal point to the film
plane when the lens is focused at infinity.
------------------
Focal point, focus
When light rays enter a convex lens parallel to the optical axis, an ideal lens will converge all the light rays to a
single point from which the rays again fan out in a cone shape. This point at which all rays converge is called
the focal point. A familiar example of this is when a magnifying glass is used to focus the rays of the sun to a
small circle on a piece of paper or other surface; the point at which the circle is smallest is the focal point. In
optical terminology, a focal point is further classified as being the rear or image-side focal point if it is the point
at which light rays from the subject converge on the film plane side of the lens. It is the front or object-side
focal point if it is the point at which light rays entering the lens parallel to the optical axis from the film plane
side converge on the object side of the lens.
-----------------
Hyperfocal distance
Using the depth of field principle, as a lens is gradually focused to farther subject distances, a point will
eventually be reached where the far limit of the rear depth of field will be equivalent to "infinity." The shooting
distance at this point, i.e., the closest shooting distance at which "infinity" falls within the depth of field, is
called the hyperfocal distance. The hyperfocal distance can be determined as follows:
Hyperfocal distance = f2 / (d • F)
f: focal length
F: F number
d: minimum circle of confusion diameter
Thus, by presetting the lens to the hyperfocal distance, the depth of field will extend from a distance equal to
half the hyperfocal distance to infinity. This method is useful for presetting a large depth of field and taking
snapshots without having to worry about adjusting the lens focus, especially when using a wide-angle lens. (For
example, when the EF 24mm is set to f/11and the shooting distance is set to the hyperfocal distance of
approximately 1.5m/4.9ft, all subjects within a range of approximately 70cm/2.3ft from the camera to infinity will
be in focus.)
----------------------
Image magnification
The ratio (length ratio) between the actual subject size and the size of the image reproduced on film. A macro
lens with a magnification indication of 1:1 can reproduce an image on film the same size as the original subject
(actual size). Magnification is generally expressed as a proportional value indicating the size of the image
compared to the actual subject. (For example, a magnification of 1:4 is expressed as 0.25x.)
----------------
Image Stabilizer
A superb new technology that allows the lens to sense movement from "shake" or vibrations, and instantly apply
an optical correction by moving a group of lens elements. The improvement in steadiness can be seen even in
the viewfinder, and most users find they can shoot hand-held or on a monopod at shutter speeds about two
stops slower than previously possible and consistently get sharp images.
----------------------
Polarized light
Since light is a type of electromagnetic wave, it can be thought of as uniformly vibrating in all directions in a
plane perpendicular to the direction of propagation. This type of light is called natural light (or natural polarized
light). If the direction of vibration of natural light becomes polarized for some reason, that light is called
polarized light. When natural light is reflected from the surface of glass or water, for example, the reflected light
vibrates in one direction only and is completely polarized. Also, on a sunny day the light from the area of the sky
at a 90° angle from the sun becomes polarized due to the effect of air molecules and particles in the
atmosphere. The half-mirrors used in autofocus SLR cameras also cause light polarization.
-------------------
Resolution
The resolution of a lens indicates the capacity of reproduction of a subject point of the lens. The resolution of
the final photograph depends on three factors: the resolution of the lens, the resolution of the film, and the
resolution of the printing paper. Resolution is evaluated by photographing, at a specified magnification, a chart
containing groups of black and white stripes that gradually decrease in narrowness, then using a microscope to
observe the negative image at a magnification of 50x. It is common to hear resolution expressed as a numerical
value such as 50 lines or 100 lines. This value indicates the number of lines per millimeter of the smallest black
and white line pattern which can be clearly recorded on the film. To test the resolution of a lens alone, a
method is used in which a fine resolution chart is positioned in the location corresponding to the film plane and
projected through the test lens onto a screen. The numerical value used for expressing resolving power is only
an indication of the degree of resolution possible, and does not indicate resolution clarity or contrast.
-----------------
Shooting distance (camera distance)
The distance from the film plane (focal plane) to the subject. The position of the film plane is indicated on the
top of most cameras by a "" symbol.
-------------------------
Stop/diaphragm/aperture
The opening which adjusts the diameter of the group of light rays passing through the lens. In interchangeable
lenses used with single lens reflex cameras, this mechanism is usually constructed as an iris diaphragm consisting
of several blades which can be moved to continuously vary the opening diameter. With conventional SLR camera
lenses, the aperture is adjusted by turning an aperture ring on the lens barrel. With modern camera lenses,
however, aperture adjustment is commonly controlled by operating an electronic dial on the camera body.
------------
-------------------------
Telephoto ratio
The ratio between the overall length of a telephoto lens and its focal length is called the telephoto ratio. Put
another way, it is the value of the distance from the apex of the frontmost lens element to the focal plane
divided by the focal length. For telephoto lenses, this value is less than one. For reference, the telephoto ratio
of the EF 300mm f/2.8L USM is 0.91 , and that of the EF 600mm f/4L USM is 0.78.
-------Telephoto type (teletype) lens
With general photographic lenses, the overall length of a lens (the distance from the apex of the frontmost lens
element to the focal plane) is longer than its focal length. This is not usually the case with lenses of particularly
long focal length, however, since using a normal lens construction would result in a very large, unwieldy lens. To
keep the size of such a lens manageable while still providing a long focal length, a concave (negative) lens
assembly is placed behind the main convex (positive) lens assembly, resulting in a lens which is shorter than its
focal length. Lenses of this type are called telephoto lenses. In a telephoto lens, the second principal point is
located in front of the frontmost lens element.
-------------------
What is “light”?
According to the dictionary, Light is defined variously as:
1. Something that makes things visible or affords illumination; an illuminating agent or source, as the sun, a
lamp, or a beacon:
2. Electromagnetic radiation to which the organs of sight react, ranging in wavelength from about 4000 to
7700 angstrom units and is propagated at a speed of about 186,300 miles per second, and including a similar
form of radiant energy that does not affect the retina, as ultraviolet or infrared rays;
3. A gleam or sparkle, as in the eyes;
4. A particular light or illumination in which an object seen takes on a certain appearance;
5. A person who is an illuminating or shining example; luminary;
6. Mental or spiritual illumination or enlightenment;
7. The aspect in which a thing appears or is regarded.
The definition most indispensable to the understanding of light as used in photography is 2 above. Types of
electromagnetic radiation vary according to wavelength. Starting from the shortest wavelengths,
electromagnetic radiation can be classified into (special form enter) rays, X rays, ultraviolet light rays, visible
light rays, infrared light rays, far-infrared light rays, microwave radiation, ultrashort wave radiation (VHF), short
-wave radiation, medium wave radiation (MF) and long wave radiation. In photography, the most utilized
wavelengths are in the visible light region (400nm-700nm).
Since light is a type of electromagnetic radiation, it can be thought of as a type of wave in the category of
"light waves." A light wave can be regarded as an electromagnetic wave in which an electric field and magnetic
field vibrate at right angles to each other in a plane perpendicular to the direction of propagation. The two
elements of a light wave which can actually be detected by the human eye are the wavelength and amplitude.
Differences in wavelength are sensed as differences in color (within the visible light range) and differences in
amplitude are sensed as differences in brightness (light intensity). The third element which cannot be detected
by the human eye is the direction of vibration within the plane perpendicular to the light wave's direction of
propagation.
-------------------------------------------------------------------
