Objective

Lenses

Commonly called the eyes of our cameras, lenses in fact are very much more. As the all-important system that actually forms an image on the film, we may rightfully call them the "heart" of our camera, for it is the lens that determines the quality of our pictures.

But even that is only half the story. Because there would be no truly versatile SLR camera without interchangeable lenses, and where would photography be without today's SLRs? In the hands of creative photographers, interchangeable lenses turn into subtle instruments controlling macro, angle, perspective, and composition.

Thus, we have lenses of almost any imaginable focal length and speed, for a great variety of different uses. And while this

A much-used photographic test: "depth of field" is a measure of the area in front of and behind the actual plane of focus which is still recognized as "sharp" by the human eye. This zone of sharpness is essentially determined by three factors, illustrated in the diagrams opposite. First, we have the aperture used for exposure (A): the wider the aperture, that is, the smaller the f-number, the shallower the depth of field. Diagram (B) shows the effect of focusing distance: the shorter the distance at which a lens is focused, the shallower the depth of field. Lastly, diagram (C) illustrates the third factor, namely focal length: here also, depth of field becomes shallower as focal length goes up.

In practice, this means that in order to make a person stand out against distracting background detail, you should use a lens of longer focal length at the widest possible aperture and a relatively short distance. Conversely, sharp reproduction from very close to very far would call for a short focal length, small aperture (high f-number), and a medium focusing distance.

But interchangeable lenses not only serve to control depth of field. The use of different focal lengths covering different angles gives us control over perspective. As long as we use different focal lengths from one and the same place, only angular coverage will change. However, if we combine a change of focal length with one of camera station, we can either make the difference in size between near and far (wide-angle perspective) or play it down by using a telephoto lens.

Magic glass

Glass is a very special, almost magic material whose beauty and extraordinary capabilities have been a stimulus to man's imagination for thousands of years. Ingenious minds and skillful hands have given it myriad shapes and harnessed its light-refracting power to obtain those marvels of advanced optical technology: photographic lenses reproducing the world around us with the utmost fidelity, clarity and brilliance.

It is a long way from glass as a raw material to one of Canon's high-performance FD lenses. The problems confronting the optical designer are gigantic. Sophisticated electronic computers have doubtless wrought tremendous change. But even so, it is still man who has to instruct the machine what to do.

There is no such thing as an ideal lens – much to the regret of optical designers and photographers alike. Each and every one of our optical systems is a compromise. Take a simple lens element, for example – a round piece of glass with two spherical surfaces. This will give you some sort of an image if you hold it at the right distance from a wall, opposite a window. But that's just it: if you were to record this image on film and blow it up to the size needed for our eyes to accept as a replica of the natural scene, you would find it full of imperfections. You would notice that an impressive number of aberrations (image errors) combine to spoil the quality of your image, making it generally useless for normal photographic purposes. An object point would not be reproduced as a point at all, but rather as some more, blurred disk. Light rays passing through the marginal areas of the lens would not intersect in the same plane as rays traveling along the optical axis. Nor would the different components of visible light – blue, yellow, and red – come to a common focus. And while your film would be more or less flat, you would have to discover that the plane of best focus in your image is not a true plane at all but some kind of S-curve, again throwing part of your picture out of focus. And as if all that were not enough, you might find that a rectangle is deformed either into a barrel or a pincushion, leaving you to wonder why you ever did take this image for a replica of your subject in the first place.

What we have described here in very general terms are variously known in optical theory as chromatic aberration, "coma error", spherical aberration, curvature of field, distortion, astigmatism, coma, etc. You may now begin to appreciate the complexity of correcting an optical system for the numerous image errors. By carefully selecting different types of optical glass for the different lens elements and combining these into suitably spaced components, in addition to varying their radii of curvature, optical designers have been able to work genuine miracles, producing lenses of ever higher resolution, better contrast rendition, and greater freedom from flare and reflections. In more recent times, these endeavors have been greatly boosted by two major developments: the creation of exotic new glass types with particularly desirable dispersion characteristics and the tremendous advances made in computer technology, which have made it possible to trace many more rays through an optical system than had ever been possible in the past. As a result, optical designers have been able to optimize their formulas to a degree that seemed completely unattainable even twenty years ago.

Although the general quality and performance of photographic lenses have thus been improved immeasurably in the recent past, there is still our very interesting "little difference" – every manufacturer has his own know-how, experience and techniques. And since approaches and solutions vary, it is only natural that the products of different manufacturers should have their own specific traits, their own "personality" so to speak.

Canon lenses do have quite a distinctive "personality"; they are generally accepted as being among the most advanced and most powerful optical systems that are made anywhere in the world today. Their "make" is flawless in every sense of the word. In fact, there are quite a number of developments that Canon has pioneered and that have become "general state of the art". Others again remain exclusive manufacturing secrets, and this very distinctive trait you will find only in Canon lenses and nowhere else.

Perhaps it's not a bad idea to invite you now to take a look behind the scenes of a Canon lens on its way from the raw material to a finished product.

Right now, there are more than 250 different types of optical glass available to Canon's optical designers for selection according to their refractive index and dispersion characteristics. Glass making itself is an extremely slow and laborious process, but the type of glass used in optical systems is a very special blend indeed. The different ingredients, chosen to the most exacting standards, are carefully mixed and melted in special fire-clay crucibles at temperatures of up to 1,700°C [3]. The mixture is constantly stirred until no further "gassing" occurs and all bubbles have been removed.

Next, the melt is allowed to cool down very slowly, a process which may extend over several weeks. As the crucible cools down, the glass tends to break up into pass [4] from which only about 30% are selected for further processing. The entire rest of the material is unusable due to imperfections such as bubbles, stones, or veins.

The irregularly shaped glass blocks are then re-heated to about 900°C and molded into so-called blanks of approximately the final shape of the optical component to be produced [5].

Other, more advanced, continuous smelting techniques involve the use of platinum troughs or crucibles into which the ingredients are continuously fed. After the glass has passed various temperature-controlled stirring stages, it is automatically poured into suitable molds. The resulting blanks are then carefully cooled, or "annealed", to remove internal stresses. These continuous techniques are very economical in large batch production.

Now the pre-molded blanks can be passed on for roughing, grinding, and finally, polishing to their ultimate shape and surface quality. Elements for Canon FD lenses are polished to within 1/10,000 mm. It goes without saying that each of these operations is followed by stringent tests and inspections. After polishing, for example, the curvature of the lens elements is tested by placing them in contact with a so-called test plate – a glass block polished flat on one side, with the specific radius accurately polished on the other. The interference fringes – or Newton's rings – formed in the extremely thin layer of air between the two surfaces are a very reliable measure of accuracy.

The next step in line is called "centring". This consists of grinding the edge of the lens to the specified diameter, making sure that the mechanical center and the optical axis of the lens are in perfect incidence.

When the lenses have thus been centered and thoroughly checked for proper radius, thickness, and freedom from optical defects, they are cleaned in special solutions agitated by sound [6].

At last, the optical elements as such are ready. And still, one very important process has to follow before they can be mounted: anti-reflection coating [7]. Used without such treatment, every single glass-in-air surface would reflect fully 4% of the incident light. In the multi-element systems frequently used today for extreme focal lengths, speed, or versatility, this can easily add up to some 50% – with the result that only half the incident light would actually reach the film. And the other half would not simply be "lost". Quite a sizable portion would stray in the optical system and reach the film "through the back door", casting a veil of image-degrading flare over our picture.

This is why all air-to-glass surfaces of Canon lenses are Spectra-coated in a vacuum chamber with special films only about 100 millimicrons thick [8]. In some cases, where the refractive index of the glass type used, the location of the element within the optical system, or other criteria so warrant, the elements are even multi-coated by the Canon Super Spectra technique. This method effectively reduces reflection from individual lens surfaces to as little as 0.3%. The result of coating is not only considerably higher light transmission but also improved contrast and color rendition.

While optical production has been going on, other sections of the company have been busy preparing the mechanical mounts which will combine the different elements into one optical system. Canon FD lenses, here also, the utmost precision and extremely narrow tolerances are indispensable. Since Canon has successfully automated a large part of its production, many of the machine tools used have been specially developed and built by the company [9]. And when the final touches have been added, each of these lenses faces the most stringent test of all: Canon's own OTF test computer [10], which automatically checks their resolving power, contrast rendition, and overall performance. Only when they have passed this final test have Canon FD lenses taken the last hurdle on their way to you.

Telephoto and super-telephoto lenses

Today, we are enjoying a remarkable degree of optical freedom. We are able to approach our subject almost without effort, without actually having to move up to it. And, to be sure, holding a camera right under someone's nose is not always such an agreeable thing to do, nor would all our subjects be particularly enthusiastic about it. So why not use a much simpler and more rewarding approach: a long-focus lens, of which there are roughly a dozen in the FD Series – not even counting special-purpose lenses. There is a choice of lenses between 85 mm and 800 mm that are suitable for full-aperture metering and AF control. If you don't mind metering the light with the lens stopped down, there is also an FL 1200 mm. And, of course, you can always order a 5200 mm lens!

Long-focus lenses tend to isolate, compress, concentrate. They pick an impressive detail which, properly presented, will speak a much clearer language than a whole bagful. Hence, they probably come closest to the essence of pictorial photography: capturing a representative part of the whole. Then there is their quality of ever more selective focus: as focal length increases, depth of field becomes shallower and the potential for selective focusing ever greater. Your subject stands out against a blurred background with an almost three-dimensional quality. In fact, distracting background detail can be eliminated almost completely. Small wonder, then, that professional photographers prefer long-focus lenses. Up to 300 or 400 mm, they are excellent for portraiture or hand-held candid shots; in short, for anything connected with people and their environment. Only beyond this limit do we enter the field of "long-distance photography" proper.

The latest achievement of Canon in the construction of long-focus lenses is internal focusing, which was used for the first time in the FD 400 mm f/4.5 SSC and is now also incorporated in the FD 300 mm f/5.6 SSC, FD 600 mm f/4.5 SSC, and FD 800 mm f/5.6 SSC. Focusing is here achieved by relatively slight axial motion of the rear component, without changing the overall mechanical length of the lens in the least. Thus, there is no bulky lens extension; the center of gravity does not shift during focusing, and the pitch of the focusing cam can be reduced at the longer distances, giving higher focusing accuracy in that range.

Fluorite lenses

Normal photographic lenses are usually corrected for two wavelengths in the visible region of the spectrum: blue and yellow. Without this so-called "achromatic correction", the blue and yellow rays from one and the same object point would intersect in different planes – and form a blurred image. But even so, the other wavelengths in the spectrum, which we see as colors, still fail to intersect all in one plane. This residual error is called the "secondary spectrum". In general-purpose photographic lenses, this is not normally found disturbing. However, there are cases where chromatic correction has to be carried one step further: process lenses, for instance, are corrected for a third color – red. These "apochromatic" lenses are widely used in the graphic arts.

Although their secondary spectrum has been greatly reduced, there is a limit to what can be done with optical glass alone.

There is one nasty little catch about the secondary spectrum: it increases as a function of focal length. In other words, the deeper we get into the telephoto range, the deeper we get into trouble. That is why Canon engineers tried to break the deadlock by substituting at least one or two elements of a telephoto system by some other material than optical glass. After years of research, they settled on an artificial crystal called calcium fluoride, a material that promised to work optical miracles if only it were available in sufficient size, purity, and quantity! After extensive research, Canon finally devised a method of "growing" artificial calcium fluoride crystals that were pure and large enough to be ground into lens elements. Canon fluorite lenses had been born.

The FL-F 300 mm f/5.6 and the FL-F 500 mm f/5.6 were the first "out-of-this-world telephotos" introduced by Canon in 1969. The practically complete elimination of the secondary spectrum achieved in these lenses left professional photographers speechless. Another "optical sound barrier" had been broken, another "first" added to Canon's impressive line of optical credentials.

Meanwhile, a special high-speed version has been added to this unique series: the FD-F 300 mm f/2.8 SSC.

Zoom lenses

Not so long ago, it was taken for granted that a lens allowing continuous variation of focal length over a certain range – a so-called zoom lens – could not possibly have the same high performance as separate lenses of fixed focal length. And that seemed only natural, because zoom lenses are pretty complex optical systems composed of many more elements than most ordinary photographic lenses.

Well, the picture has changed, at least as far as Canon's zoom lenses in the FD Series are concerned. Optical progress and new design principles have resulted in FD zoom lenses of truly outstanding performance at any focal length – even in the wide-angle range, which at first seemed almost inaccessible to zoom systems.

By now, there is practically continuous zoom coverage for your Canon SLR from a mere 28 mm right up to 300 mm. Photographers favoring short focal lengths will find the answer to their prayers in the FD 28-50 mm f/3.5 SSC, which, incidentally, is based on Canon's new two-group design principle explained below in greater detail. The FD 35-70 mm f/2.8-3.5 SSC, likewise a two-group design, is another compact zoom giving you tremendous freedom of motion around the normal focal length, from the most widely used wide-angle focal length up to practically semi-telephoto, to be exact.

On the telephoto side, you have a choice of three Canon zooms: the FD 80-200 mm f/4 SSC as a compact, general-purpose telephoto lens of relatively high speed and superb resolution, contrast, and color rendition; the FD 100-200 mm f/5.6 SC as a moderately priced telephoto zoom intended primarily for the amateur who will content himself with somewhat lesser speed; and the FD 85-300 mm f/4.5 SSC as a very fast "big gun" designed above all for shooting from a tripod.

Each of these zoom lenses actually replaces an entire set of ordinary lenses of fixed focal length. Take the FD 80-200 mm, for example, which not only can give you the same coverage as an FD 85 mm, 100 mm, 135 mm, and 200 mm but all the intermediate settings to which there is just one answer: a zoom system. Composing your picture and filling your frame has never been easier.

In the past, zoom lenses were mostly composed of four groups of lens elements. A typical point in case is the FD 85-300 mm f/4.5 SSC, shown set to 300 mm in diagram (A) and to 85 mm in (B). While this design principle is entirely adequate for longer focal lengths, it would make wide-angle zoom lenses disproportionately heavy, bulky, and complex. Canon therefore perfected a design principle which relies on only two groups of components that shift in relation to each other as focal length is varied. As an example, diagram (C) shows the FD 35-70 mm f/2.8-3.5 SSC in its 70 mm setting, and (D) in the 35 mm setting. The two-group principle allows a much more compact retrofocus construction and higher optical extraction. It will be noted that in this case the diaphragm is shifted together with the rear group.

Macro lenses

To start with, you should not take the term "macro lens" too literally, because it gives a rather one-sided picture of this very interesting type of lens. To be sure, it is an avowed purpose of these lenses to offer maximum optical performance even in the close-up and macro ranges for which our photographic lenses are not normally corrected. On the contrary, ordinary photographic lenses have been corrected for infinity; they do not have a long-enough focusing mechanism to allow close shots up to a reproduction ratio of at least 1:2, and they are mainly designed for high speed and thus remain a compromise. While this compromise is more than enough for the purposes of pictorial photography, it does begin to show its limits as soon as we enter the sphere of extreme close-ups and try to copy documents or similar originals, to name just one example. It is here where the macro lens comes fully into its own because it is a "no-compromise lens". At the expense of high speed, it is designed for unusually high resolution, perfect field flattening, and uniform correction right up to extremely short camera-to-subject distances. Moreover, its ordinary focusing mount goes up to 1:2, and with a special extension tube, it will even take life-size pictures.

All these advantages of a macro lens, however, suggest quite a different additional use: as long as speed is of no great importance, a macro lens is the best "standard" lens you could desire. The fact that in the Canon FD Series this type of high-performance lens is also available in the telephoto range in the form of the FD 100 mm f/4 SC makes this proposition all the more attractive.

Speaking of lenses distinguished by special design features, there is another species in the Canon line that is unique in the 35 mm SLR field: a lens that cannot only be shifted at right angles to the optical axis but also offers a swing movement much like the front of a large-format camera. This TS 35 mm f/2.8 SSC was primarily developed for architectural and industrial photography, where the elimination of converging verticals is absolutely essential. But apart from this, it also allows depth-of-field control by the Scheimpflug rule, providing almost incredible depth of field without stopping down. This feature is in high demand, among other things, in industrial photography because more often than not this is the only way to sharply reproduce an extensive object that is not parallel to the film plane.

Tangible progress - Canon FD lenses

When the first FD lenses were introduced together with the Canon F-1, a new era began to dawn for Canon fans everywhere: the era of full-aperture TTL metering and the latest optical advances put into practice in the form of a lens series designed to satisfy even the most exacting professional. By now, this lens series has grown into a powerful optical arsenal. That is the common basis of all the cameras in the Canon Reflex System: the F-1, EF, AE-1, AT-1, and FTb.

A closer study of the FD Series clearly reveals the tangible progress made in optical design and manufacturing techniques during the past decade. New glass types of high refractive index laid the basis for entirely new design concepts. Aided by their own, meticulously drafted computer programs, Canon engineers started exploring new solutions, continually improving the performance, speed, and compactness of their designs along the way. New laser and computer-supported testing techniques were instrumental in reaching an ever higher degree of optical and mechanical precision. More recently, automation was given top priority, with the result that by now many of the operations required to make the most popular FD lenses are performed either automatically or with only a minimum of human interference. These innovations have enabled Canon to stay one step ahead of rising costs that can only be offset by more rational production.

Tangible proof of progress are the savings in size and weight that Canon has been able to make in its new FD lenses. Take long focal lengths, for example. The FD 200 mm f/2.8 SSC was the first telephoto lens in which Canon drastically reduced the diameter of the lens elements right behind the front component. The same principle has since been used in all new lenses in this category, adding immeasurably to the handling ease of these long-focus systems. In the new FD lenses of 300 mm and up, moreover, Canon has incorporated another new design principle which it was the first to introduce in the market: internal focusing. Instead of moving the entire optical system forward for focusing on subjects closer than infinity, as is normal practice, the focusing ring of the new Canon FD lenses of 300 mm, 400 mm, 600 mm, and 800 mm only acts on the relatively small rear component of the system. In other words, there is absolutely no change in mechanical length as the lens is focused. And if you have ever handled a lens of that focal length, you will appreciate what this means in terms of stability. Instead of becoming top-heavy, the lens-camera unit remains perfectly stable, without any shift in its center of gravity. Moreover, the lenses can be designed for a much shorter minimum focusing distance than before, and the focusing action can be made "non-linear". This means that at the longer distances, focusing requires a slightly greater rotation of the focusing ring and thus is much smoother and more precise than would be possible with a normal helicoidal mount.

Filters in these long-focus lenses of such unusually high speed would have to be very big if they had to be attached to the front lens. This is why Canon has given them a place right inside the lens tube, behind the rear component. At this point in the light path, the filters can be very small. Changing them with their slide-in mounts is a matter of seconds. And that's just about as long as a change of filters should take in a truly advanced long-focus lens.

Canon filters and their uses

Filters for black-and-white photography:

• Y1: Light yellow filter. Darkens blue and lightens yellow. Improves sky rendition in black-and-white photography.
• Y3: Standard yellow filter for better contrast in black-and-white photography.
• G1: Light green filter for black-and-white. Holds back red, renders green lighter.
• O1: Orange filter for even higher black-and-white contrast than with Y3. Very effective for cloud conditions.
• R1: Red filter for monochrome and infrared photography. Renders red practically white and blue sky almost black. Effectively cuts through haze.

Filters for color photography:

• Skylight: Slightly tinted (amber) filter for color photography, for warmer rendition of colors and suppression of blue haze.
• UV: Absorbs ultraviolet rays, presenting a blue cast in color photography and lack of focus in high-UV environments (e.g., at the beach, in high mountains, etc.).
• CCA4-8-12: Conversion filters (amber) of different color density for lowering the color temperature. The type 12 filter will convert Tungsten-type film for daylight shooting.
• CCB4-8-12: Conversion filters (blue) of different color density for raising the color temperature. The type 12 filter will convert daylight film for shooting with artificial light.
• ND4, ND8: Neutral-density gray filters reducing the intensity of incident light by two and three f-stops, respectively.

Close-up lenses:

• Close-up lenses: These lenses are designed for close-up photography, allowing for higher magnification and reduced minimum focusing distances.

Technical data of Canon SLR lenses

FD lenses for full-aperture metering and AE control. FL lenses for stop-down metering.

*With extension tube FD 25
**With extension tube FD 50
***Built-in lens hood
1) Filter of insertion type with holder
2) Close-focusing capability

Freedom

Interchangeable lenses – that's freedom of expression, freedom of speaking your mind photographically, of conveying a message, making a point, or simply capturing a subject with the most appropriate optical means. Freedom which in Canon SLR photography means just a twist of your wrist, a turn of the sturdy bayonet ring of Canon's unique breech-lock mount. Within seconds, one lens can thus be changed for another – hundreds, thousands of times, as often as you may wish during the long life of your Canon camera and lenses. And there's no need to worry about wear. Canon lenses are not rotated in the camera body. Their precision seating faces do not rub against their counterparts in the camera. The lenses are inserted straight – in the position in which they are used. Turning a spring-loaded bayonet ring will do the trick of locking them safely on the camera. A design that gives you an additional degree of freedom – the freedom to vary your shooting and viewing angles as frequently as your imagination or requirements demand.

Since literally millions of Canon SLRs are in use all over the world, it is not surprising that independent lens makers have been trying to cash in on this market. And every once in a while, you will find lenses of other manufacture being offered with a breech-lock mount to suit your Canon SLR. To put the record straight, it might be mentioned here that some of the meter and diaphragm-coupling elements have different functions in different types of Canon SLR. Since Canon is using automatic aperture control instead of the automatic shutter-speed control employed in a number of other advanced SLRs in the market, lens-mount specifications are of the utmost importance.

Needless to say that Canon will fully guarantee only its own maximum-precision FD lenses for perfect operation with any of the Canon SLR cameras. As a matter of fact, this guarantee also covers all other lenses described in this brochure, although, strictly speaking, they may not bear the "FD" label and thus be designed only for stop-down metering or manual aperture control, such as the FL types or the TS lens.

The comparative pictures on these pages illustrate the change in angle of view which different focal lengths give from one and the same point. Also, they very nicely demonstrate the wide range of expression enjoyed by Canon SLR photographers.