The Importance of TTL Metering
One of the breakthrough in the course of development in SLR was the incorporation
of TTL metering in the camera body. First developed by Asahi Pentax on the Spotmetic
during the sixties. The addition of a light metering system in the body of the single
lens reflex was a natural step in the evolution of the camera. The meter reads the
exact amount of light passing through the lens (TTL) as reflected by the subject.
This is a definite advantage of an SLR camera for it allows the meter to measure
the light quickly and accurately even, for example, when taking a picture of a distant
subject using a telephoto lens. The through-the-lens metering systems also provide
correct readings even with filters over the lens, automatically accounting for the
additional exposure required. (Note: with the Canon F-1n, Canon F-1(Original), FTb, FT, Pellix and TL, exposure adjustment is necessary
when using a polarizing filter). Correct exposure can be obtained with TTL metering
even when an accessory such as an extension tube or bellows is placed between the
lens and the camera body. Thus TTL metering further heightens the flexibility and
operational ease incorporated in an SLR camera. Further, the benefit of TTL metering
system has also being deployed and extended to flash photography. As long as the
subject is within your dedicated flash output range, flash exposure control has never
been so accurate and simple. Regardless of any combination of lenses used, filter
attachments, complicated multiple-flash setup, photomicro or even syncro-sunlight
photography.
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There are generally three ways to measure the light entering the lens: stopped-down, full-aperture and flash metering. During stopped-down metering, the lens must be closed (stopped down) to the shooting aperture (the aperture you set or the camera's electronic circuitry decides). As a result, less light enters the lens causing the viewfinder to darken. The smaller the aperture set, the darker the viewfinder becomes (and usually degree of depth of field extends as well). Framing and focusing become difficult if not performed with the lens at its maximum aperture. |
With full aperture metering, metering and viewing are done with the lens at its widest opening where the viewfinder is brightest to see. When you press the shutter release button, the diaphragm automatically closes down to the predetermined lens opening, the shutter opens and the exposure is made after which the diaphragm automatically reopens to maximum aperture.
Theoretically, stopped down metering
should be more accurate, since the metering is done at the preset aperture value,
but it poses inconvenience during focusing. Virtually ALL of Canon's manual focus
SLRs use full-aperture metering system enabling focusing and composing to be performed
with greater ease. In flash photography, you can either choose manual, auto or programmed
flash. Manual flash requires the user to set aperture on the lens and sync speed
on the camera body manually, while some automatic bodies will set to its maximum
permissible sync speed when a dedicated flash unit is used. Auto flash usually requires
a user to set the aperture on the lens to the few settings the flash recommends.
Both combination of aperture and shutter speed in Programmed AE flash will be handled
by the camera (usually required to set the lens to AUTO setting or minimum aperture
value).
The spec used on the later Canon FD lenses come with a lens mount has all the convenience
of bayonet mount of one-twist mounting. However, the unique mount system causes the
lens barrel to turn but not the lens flange itself. This means that there is virtually
no wear and tear on moving parts. In addition to the FD series, older Canon lens
series include the FD (original type), FL and R series. The original FD lenses perform
in virtually the same manner as the FD lenses except that mounting is slightly different,
of which it requires the user to turn a mounting ring on the lens to secure the mount.
The earlier lens series were also similar in operation with older FD lenses when
process of mounting relates. But they differ both in diaphragm and metering operation.
The FL lenses, for instance may be used for stopped-down metering or stopped-down
automation on Canon cameras which provide that mode besides, manual full-aperture
operation is also possible. They have an "A-M" ring which may can be used
in place of the stopped-down lever. Canon R-series lenses, will only operate manually
on the current Canon SLR models and may be used for stopped-down metering and stopped-down
automation on Canon cameras having this mode with MANUAL DIAPHRAGM operation only.
For camera like the Shutter Priority AE mode only body like the T-50, this may pose
some problems.
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Anyway, as far as the FD lenses relate, they have incorporated all possible combination of various photographic usage into their design. You can adjust the aperture to suit any preferred exposure control method in manual, auto or programmed AE mode, whether you will be required them to perform in daylight AUTO or Flash AE mode in fill light situation or total darkness. Take the case of the most advance Canon FD mount SLR camera, the Canon T90 of 1986 which also was the first Canon model to feature TTL flash exposure control and as well as the exclusive E-TTL flash metering system with the companion TTL flash, 300-TL. In terms of technology employed in the Canon T-90, other than the popular multi-segment ambient light and flash exposure control used currently in most AF SLRs, the flash metering used in the camera is quite up to date as with latest Canon EOS autofocus 35mm SLR cameras. |
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The T-90 was so sophisticated in its exposure control system that it has a total of EIGHT Exposure Modes in Shutter priority AE; Aperture priority AE; Standard program AE; Variable shift program AE (selectable out of 7 programs); Manual; Stopped down AE; Stopped down (fixed index) metering and Flash AE (possible with specified Canon Speedlites). Despite has to cope with such complexity in exposure control, the camera also has a few metering system to select from, including the Olympus pioneered multi-spot metering with highlight and shadow control. None of the FD lenses regardless old or newer version posed any serious problem as far as compatibility issue is concerned to match such demanding technologies employed in a highly advance SLR system such as the Canon T-90. This actually explained how far the original design of the FDn lenses Canon has taken into consideration to future needs. |
The Joy of using Interchangeable Lenses
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The versatility of a single lens reflex camera is most apparent with the use of interchangeable lenses. Though perhaps it is the greatest advantage of owning an SLR, its flexibility is even further enhanced by the system of accessories that surround it. Depending on the camera, interchangeable screens, viewfinders, motor drives, power winders, bellows, electronic flash units, data backs and other accessories can be attached enabling virtually any image to be taken. |
The creation of a system designed to meet your unique personal needs is one of the greatest pleasures in owning an SLR. With the use of interchangeable lenses and accessories. As far as the FD lenses is concerned, as a whole - it has a total of more than 60 + lenses of different types, focal length, speeds, functions and angle of views to match your vision and photographic requirements.
And within the FD family of lenses,
there is another series of optics that were especially tailored design and produced
to meet the demanding professional needs. It was generally referred as Canon 'L'
Series lenses and that could possibly formed the basis for claim Canon has one of
the most respectable name in the business.
Lens Construction and Types
(Credit: Info contained herein courtesy
of Canon Marketing)
"Lens" is a simple word, but a lens consists of a complicated assembly
of various lens elements in addition to the barrel, diaphragm, mount and other mechanical
components. Of these, the construction of the lens proper is particularly important.
Thorough knowledge of the relationship between the camera body and the lens is important
if you are going to make the most of the wide range of lenses within a system. Here,
we will consider the various components that make up a lens, the function and role
of these elements and their relationship to the camera body.
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While it is possible to take a picture with just one simple convex lens, the results would not be sharp over the whole field. Color reproduction would also be less than desirable. To make a lens capable of producing sharp, undistorted images requires an assembly of several convex and concave lenses. You may have noticed that lens specification tables usually have headings that read "groups" and "elements"; these figures indicate how many components make up the lens. For example, two or more elements (simple lenses) joined together count as one group. The number of elements and groups depend on lens design. |
However, the number of elements and groups in a lens increases as aperture grows larger, angle of view grows wider and, in the case of a zoom lens, more than one focal length is incorporated in its design. These multiple elements and their design improve overall lens performance. There is an infinite variety of concave and convex lens combinations. However, when the purpose and performance of lenses have similarities (for example, wide-angle lenses), the lens combinations closely resemble each other. By grouping similar lenses, it is possible to classify them into certain types.
The majority of lenses can be classified as symmetrical or asymmetrical types. A symmetrical lens design consists of identical elements on both sides of the lens diaphragm; the representative example is the Gauss type. Most standard lenses are designed closely along this line. A symmetrical lenses are types in which the structure and positions of the lenses in front of and behind the diaphragm differ. Typical examples are the Triplet and Tessar types. Lens designs commonly used today include Xenotar, Sonnar, Ernostar and Retrofocus. Among the special lens types there are the mirror reflex, or catadioptric, lenses and zoom lenses.
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Various Lens Types |
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The Mechanics of Focusing
Focusing on a particular subject involves moving the lens in relation to the film
plane - either closer or farther away. This is usually accomplished with a helicoid
arrangement. A helicoid is actually a series of threads on the lens barrel nested
in a second series of threads. As you turn the focusing ring the barrel rides on
the helicoid, moving the lens elements. With most designs the lens itself does not
rotate; instead, it moves back and forth. Normally it takes less than one complete
turn of the focusing ring to move the lens from its closest focusing distance to
infinity. In some lens systems, notably zoom lenses, only the front group of lenses
moves when you focus. And with long telephotos only the rear group of lenses moves
during focusing.
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Canon FD mount
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