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Canon FD 55mm F/1.2 S.S.C. AL

Standard prime lens • Film era • Discontinued

Abbreviations

FD The lens is designed for Canon 35mm film SLR cameras with the Canon FD mount.
S.S.C. Multi-layer Super Spectra coating is applied to the surfaces of lens elements. This anti-reflection coating increases light transmission, eliminates flare and ghosting, and maintains color consistence among all lens models.
AL The lens incorporates aspherical elements.

Model history (3)

■Canon FD 55mm F/1.2 ALA8 - 60.60m⌀58 1971 ●
■Canon FD 55mm F/1.2 S.S.C. ALA8 - 60.60m⌀58 1973 ●
■Canon FD 55mm F/1.2 S.S.C. AsphericalA8 - 60.60m⌀58 1975 ●

Features highlight

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Ultra fast
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1
ASPH
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F.E.
•
MF
•
Auto
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8 blades
•
Compact
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⌀58
filters
•
TC

Specification

Production details:
Announced:March 1973
Production status:● Discontinued
Original name:CANON LENS FD 55mm 1:1.2 S.S.C. AL
System:Canon FD (1971)
Optical design:
Focal length:55mm
Speed:F/1.2
Maximum format:35mm full frame
Mount and Flange focal distance:Canon FD [42mm]
Diagonal angle of view:42.9°
Lens construction:8 elements in 6 groups
1 ASPH
Floating element system
Diaphragm mechanism:
Diaphragm type:Automatic
Aperture control:Aperture ring (Manual settings + Auto Exposure setting)
Number of blades:8 (eight)
Focusing:
Closest focusing distance:0.6m
Magnification ratio:1:9.1 at the closest focusing distance
Focusing modes:Manual focus only
Manual focus control:Focusing ring
Physical characteristics:
Weight:575g
Maximum diameter x Length:⌀75.8×55mm
Accessories:
Filters:Screw-type 58mm
Lens hood:BS-58 - Bayonet-type round
Teleconverters:Canon Extender FD 2X-B → 110mm F/2.4
Sources of data:
1. Canon FD lenses booklet (PUB. CE1001J) (December 1974).
2. Canon FD interchangeable lenses instructions (PUB. A5368) (February 1974).
3. Canon EF instructions (PUB. IE 1008P) (May 1976).
4. Canon F-1 booklet (PUB. CE1017F) (December 1975).
5. Canon F-1 booklet (PUB. NO5367Q) (September 1974).
6. The pinnacle of optical perfection. Canon FD lenses booklet (PUB. CE1006F) (March 1973).

Manufacturer description #1

This is a large aperture standard lens in which aspherical lenses were applied. It is a perfect lens for delineation in photography at night with full aperture opening, in ordinary photography in daytime and at close distances as well. It eliminates flare to a negligible level, to give a picture image of fine contrast.

Manufacturer description #2

This is a large aperture standard lens using an aspherical surface, which provides highest image delineation even at full-aperture opening under dim light conditions. Additionally, this lens incorporates the Floating System which enables aberration-free shooting at close subject distance. Thus, a stabilized image is obtained through the entire focusing range. Therefore, the focused image through the viewfinder can be reproduced just as it is.

For further perfection, the Super Spectra Coating is applied to this lens to maintain clearness without ghosts.

Canon calls this lens the "perfect lens" because it provides sharpness under all photographic conditions.

From the Modern Photography magazine (November 1978)

With current ASA 400 color films pushable to E.I. 800 and fine quality 50mm f/1.4 lenses available from numerous camera manufacturers, who needs "super-speed" lenses? Haven't the f/1s and f/1.2s of the world been relegated to the role of extravagant, expensive, and bulky luxuries appealing mainly to snobbish gadgeteers and the handful of remaining "low light" photojournalists? Perhaps, to some extent, but like all great half truths, these rhetorical questions hint at only part of the story. After all, super-speed lenses have always been considered specialized tools and, surprisingly, their popularity has actually increased slightly as film speeds have gotten higher.

Twenty-five years ago, when 35mm SLRs were first beginning to become popular, the "normal" lens was usually a 50mm f/2.8 or a 58mm f/2. Soon afterward, the six element f/2s were opened up a bit to f/1.9 and even up to f/1.7. Lenses faster than these were considered to be "super-speed." It didn't take long for optical engineers to discover that the six-element designs they had been using for the f/2s were simply not good enough to produce satisfactory f/1.4s. Even with the newest high-index, exotic rare-earth optical glasses which were being developed by glass manufacturers around the world, optical engineers recognized that a radical change had to be made in the design of these early super-speed lenses.

Seven-element design

Among the original super-speeds was the famous 50mm f/0.95 Canon lens which featured seven glass elements, and pieces ground out of the rearmost elements so that the lens could fit into the Canon rangefinder cameras.

But the seven-element design method was not the only approach to getting sharp-imaging super-speed lenses. Leitz engineers decided to try their hand at a six-element, four-group 50mm f/1.2 lens for the Leica with a special non-spherical surface ground and polished into two of the elements.

Two types in use today

The situation today remains pretty much at this level: The two approaches are still being used. Most f/1.4 and faster lenses today are seven-element designs. A few are made with aspheric surfaces. Most interesting is the position of Leitz. The f/1.2 Noctilux with aspheric surfaces has recently been discontinued. So Leitz-Canada, under the engineering direction of Dr. Walther Mandler, developed a satisfactory f/1.0 using the latest rare-earth glasses and no aspherics. Canon offers their f/1.2 with aspheric surfaces.

In the Leitz-Canada 50mm f/1.0 Noctilux, there is considerable vignetting toward the corners. This is not an accident; it's deliberately built in to try to reduce the horrendous off-axis flare which appears in the image, and reduces contrast and resolution. The skew rays which pass through the outer parts of the elements on their way to the off-axis image often go badly off course. So, to avoid the resulting image quality loss, the designers purposely allow some aperture falloff for the extreme off-axis (edge) image points. We conclude that it's almost unavoidable when trying to engineer a super-speed lens with a reasonable number of glass elements.

Since the aspheric surface in the Canon 55mm f/1.2 lens is close to the diaphragm, off-axis rays pass through the lens more normally than they would for an aspheric surface at the back or in the front element. As a result, the beneficial effect of the aspheric surface applies to the off-axis light rays as well. We found that the off-axis image quality for the Canon lens at maximum aperture was not noticeably poorer than it was when the lens was stopped down to f/2. In other words whatever help the aspheric surface was designed to give could be seen over the entire image format.

What aberrations seemed to be the most important in the images formed by these lenses? First of all is the spherical aberration - both rim-ray (at the extreme edges of the lens at maximum aperture) and zonal, which occurs when the lens is closed down about one stop. A very careful balance must be made between the remaining rim-ray spherical and the residual zonal spherical aberrations so that the image quality will improve, not get worse, as the lens is stopped down. Nevertheless, with these super-speed lenses you do sacrifice a small amount of image sharpness and contrast when shooting at common apertures such as f/4 or f/5.6. However, by the time you reach apertures such as f/8 and f/1 1 superspeed lenses generally perform on par with their slower (f/1.7 or f/1.4) counterparts.

Lenses polished individually

But too much zonal spherical aberration can be a serious problem, too. If there is too much of it, a definite focus shift may be encountered when the lens is focused by observing the groundglass view with the lens wide open, and the picture is taken when the lens is stopped down, say, two full stops. Canon's use of the aspheric surface helps to get rid of this sticky problem in one complete (but radical) design change. The only problem which remains is that of the smoothness and accurate polishing which is required for the aspheric surface, and which has to be done one lens at a time in the optical shop. It is to Canon's credit that the 55mm f/1.2 does perform very well, and there are few if any aberrations attributable to irregularities in the aspheric surface.

Another problem is that of visible color due to spherical aberration. It may be that the optical engineer has designed the lens with a nice balance between the rim-ray and zonal spherical aberrations for green light. But, when we put blue and red light through the same lens, we might find that the blue rim-ray is over-corrected and results in a blue flare, while the red beam is undercorrected and there is red flare visible also. The overall result is a loss of color fidelity, particularly toward edges of the format and in the finer details of the image. This color variation of spherical aberration is one of the main reasons for the large number of lens elements required in the design of fast normal-focal-length lenses. This is also the main reason why so many lenses incorporate the familiar thick pairs of elements with a strong convex surface on one end and a similar strongly concave surface at the other. Look at the diagrams of some of the f/2 or faster normal lenses and you'll find these thick meniscus pairs easily.

Because a camera lens must produce a sharp image over a relatively wide angle of view, the off-axis (edge) image quality becomes a very important and limiting factor. It turns out to be easier to design a fast lens of longer than normal focal length because it does not have to cover as wide an angle of view. But the lens elements must be larger and the aberrations even more closely corrected or balanced.

In conclusion, if the extra speed is essential, today's super-speed lenses do not force us to accept noticeably poorer image quality either at wide, intermediate or stopped down apertures. If the lens is used primarily wide open, the aspheric Canon may be the best choice. In short, while super-speed lenses remain considerably more expensive and somewhat bulkier than their slower counterparts, their overall performance is now good enough to allow them to be purchased as replacements for, rather than additions to slower lenses of similar focal length.

Other standard prime lenses in the Canon FD system

Sorted by focal length and speed, in ascending order

■Canon FD mount (15)
Canon FDn 50mm F/2A6 - 40.60m⌀52 1980 ●
Canon FD 50mm F/1.8A6 - 40.60m⌀55 1971 ●
Canon FD 50mm F/1.8 S.C. [I]A6 - 40.60m⌀55 1973 ●
Canon FD 50mm F/1.8 S.C. [II]A6 - 40.60m⌀55 1976 ●
Canon FDn 50mm F/1.8A6 - 40.60m⌀52 1979 ●
Canon FD 50mm F/1.4A7 - 60.45m⌀55 1971 ●
Canon FD 50mm F/1.4 S.S.C. [I]A7 - 60.45m⌀55 1973 ●
Canon FD 50mm F/1.4 S.S.C. [II]A7 - 60.45m⌀55 1973 ●
Canon FDn 50mm F/1.4A7 - 60.45m⌀52 1979 ●
Canon FDn 50mm F/1.2A7 - 60.50m⌀52 1980 ●
Canon FDn 50mm F/1.2LA8 - 60.50m⌀52 1980 ●
Canon FD 55mm F/1.2A7 - 50.60m⌀58 1971 ●
Canon FD 55mm F/1.2 ALA8 - 60.60m⌀58 1971 ●
Canon FD 55mm F/1.2 S.S.C.A7 - 50.60m⌀58 1973 ●
Canon FD 55mm F/1.2 S.S.C. AsphericalA8 - 60.60m⌀58 1975 ●

Lenses with similar focal length

■Interchangeable mount (1)
Tamron 58mm F/1.2 [T]
aka Taika Harigon 58mm F/1.2		P8 - 61.8 ft. 1960 ●
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Chromatic aberration

There are two kinds of chromatic aberration: longitudinal and lateral. Longitudinal chromatic aberration is a variation in location of the image plane with changes in wave lengths. It produces the image point surrounded by different colors which result in a blurred image in black-and-white pictures. Lateral chromatic aberration is a variation in image size or magnification with wave length. This aberration does not appear at axial image points but toward the surrounding area, proportional to the distance from the center of the image field. Stopping down the lens has only a limited effect on these aberrations.

Spherical aberration

Spherical aberration is caused because the lens is round and the film or image sensor is flat. Light entering the edge of the lens is more severely refracted than light entering the center of the lens. This results in a blurred image, and also causes flare (non-image forming internal reflections). Stopping down the lens minimizes spherical aberration and flare, but introduces diffraction.

Astigmatism

Astigmatism in a lens causes a point in the subject to be reproduced as a line in the image. The effect becomes worse towards the corner of the image. Stopping down the lens has very little effect.

Coma

Coma in a lens causes a circular shape in the subject to be reproduced as an oval shape in the image. Stopping down the lens has almost no effect.

Curvature of field

Curvature of field is the inability of a lens to produce a flat image of a flat subject. The image is formed instead on a curved surface. If the center of the image is in focus, the edges are out of focus and vice versa. Stopping down the lens has a limited effect.

Distortion

Distortion is the inability of a lens to capture lines as straight across the entire image area. Barrel distortion causes straight lines at the edges of the frame to bow toward the center of the image, producing a barrel shape. Pincushion distortion causes straight lines at the edges of the frame to curve in toward the lens axis. Distortion, whether barrel or pincushion type, is caused by differences in magnification; stopping down the lens has no effect at all.

The term "distortion" is also sometimes used instead of the term "aberration". In this case, other types of optical aberrations may also be meant, not necessarily geometric distortion.

Diffraction

Classically, light is thought of as always traveling in straight lines, but in reality, light waves tend to bend around nearby barriers, spreading out in the process. This phenomenon is known as diffraction and occurs when a light wave passes by a corner or through an opening. Diffraction plays a paramount role in limiting the resolving power of any lens.

Doublet

Doublet is a lens design comprised of two elements grouped together. Sometimes the two elements are cemented together, and other times they are separated by an air gap. Examples of this type of lens include achromatic close-up lenses.

Dynamic range

Dynamic range is the maximum range of tones, from darkest shadows to brightest highlights, that can be produced by a device or perceived in an image. Also called tonal range.

Resolving power

Resolving power is the ability of a lens, photographic emulsion or imaging sensor to distinguish fine detail. Resolving power is expressed in terms of lines per millimeter that are distinctly recorded in the final image.

Vignetting

Vignetting is the darkening of the corners of an image relative to the center of the image. There are three types of vignetting: optical, mechanical, and natural vignetting.

Optical vignetting is caused by the physical dimensions of a multi-element lens. Rear elements are shaded by elements in front of them, which reduces the effective lens opening for off-axis incident light. The result is a gradual decrease of the light intensity towards the image periphery. Optical vignetting is sensitive to the aperture and can be completely cured by stopping down the lens. Two or three stops are usually sufficient.

Mechanical vignetting occurs when light beams are partially blocked by external objects such as thick or stacked filters, secondary lenses, and improper lens hoods.

Natural vignetting (also known as natural illumination falloff) is not due to the blocking of light rays. The falloff is approximated by the "cosine fourth" law of illumination falloff. Wide-angle rangefinder designs are particularly prone to natural vignetting. Stopping down the lens cannot cure it.

Flare

Bright shapes or lack of contrast caused when light is scattered by the surface of the lens or reflected off the interior surfaces of the lens barrel. This is most often seen when the lens is pointed toward the sun or another bright light source. Flare can be minimized by using anti-reflection coatings, light baffles, or a lens hood.

Ghosting

Glowing patches of light that appear in a photograph due to lens flare.

Retrofocus design

Design with negative lens group(s) positioned in front of the diaphragm and positive lens group(s) positioned at the rear of the diaphragm. This provides a short focal length with a long back focus or lens-to-film distance, allowing for movement of the reflex mirror in SLR cameras. Sometimes called an inverted telephoto lens.

Anastigmat

A photographic lens completely corrected for the three main optical aberrations: spherical aberration, coma, and astigmatism.

By the mid-20th century, the vast majority of lenses were close to being anastigmatic, so most manufacturers stopped including this characteristic in lens names and/or descriptions and focused on advertising other features (anti-reflection coating, for example).

Rectilinear design

Design that does not introduce significant distortion, especially ultra-wide angle lenses that preserve straight lines and do not curve them (unlike a fisheye lens, for instance).

Focus shift

A change in the position of the plane of optimal focus, generally due to a change in focal length when using a zoom lens, and in some lenses, with a change in aperture.

Transmittance

The amount of light that passes through a lens without being either absorbed by the glass or being reflected by glass/air surfaces.

Modulation Transfer Function (MTF)

When optical designers attempt to compare the performance of optical systems, a commonly used measure is the modulation transfer function (MTF).

The components of MTF are:

The MTF of a lens is a measurement of its ability to transfer contrast at a particular resolution from the object to the image. In other words, MTF is a way to incorporate resolution and contrast into a single specification.

Knowing the MTF curves of each photographic lens and camera sensor within a system allows a designer to make the appropriate selection when optimizing for a particular resolution.

Veiling glare

Lens flare that causes loss of contrast over part or all of the image.

Anti-reflection coating

When light enters or exits an uncoated lens approximately 5% of the light is reflected back at each lens-air boundary due to the difference in refractive index. This reflected light causes flare and ghosting, which results in deterioration of image quality. To counter this, a vapor-deposited coating that reduces light reflection is applied to the lens surface. Early coatings consisted of a single thin film with the correct refractive index differences to cancel out reflections. Multi-layer coatings, introduced in the early 1970s, are made up of several such films.

Benefits of anti-reflection coating:

Circular fisheye

Produces a 180° angle of view in all directions (horizontal, vertical and diagonal).

The image circle of the lens is inscribed in the image frame.

Diagonal (full-frame) fisheye

Covers the entire image frame. For this reason diagonal fisheye lenses are often called full-frame fisheyes.

Extension ring

Extension rings can be used singly or in combination to vary the reproduction ratio of lenses. They are mounted between the camera body and the lens. As a rule, the effect becomes stronger the shorter the focal length of the lens in use, and the longer the focal length of the extension ring.

View camera

A large-format camera with a ground-glass viewfinder at the image plane for viewing and focusing. The photographer must stick his head under a cloth hood in order to see the image projected on the ground glass. Because of their 4x5-inch (or larger) negatives, these cameras can produce extremely high-quality results. View cameras also usually support movements.

135 cartridge-loaded film

43.27 24 36
  • Introduced: 1934
  • Frame size: 36 × 24mm
  • Aspect ratio: 3:2
  • Diagonal: 43.27mm
  • Area: 864mm2
  • Double perforated
  • 8 perforations per frame

120 roll film

71.22 44 56
  • Introduced: 1901
  • Frame size: 56 × 44mm
  • Aspect ratio: 11:14
  • Diagonal: 71.22mm
  • Area: 2464mm2
  • Unperforated

120 roll film

79.2 56 56
  • Introduced: 1901
  • Frame size: 56 × 56mm
  • Aspect ratio: 1:1
  • Diagonal: 79.2mm
  • Area: 3136mm2
  • Unperforated

120 roll film

89.64 56 70
  • Introduced: 1901
  • Frame size: 70 × 56mm
  • Aspect ratio: 5:4
  • Diagonal: 89.64mm
  • Area: 3920mm2
  • Unperforated

220 roll film

71.22 44 56
  • Introduced: 1965
  • Frame size: 56 × 44mm
  • Aspect ratio: 11:14
  • Diagonal: 71.22mm
  • Area: 2464mm2
  • Unperforated
  • Double the length of 120 roll film

220 roll film

79.2 56 56
  • Introduced: 1965
  • Frame size: 56 × 56mm
  • Aspect ratio: 1:1
  • Diagonal: 79.2mm
  • Area: 3136mm2
  • Unperforated
  • Double the length of 120 roll film

220 roll film

89.64 56 70
  • Introduced: 1965
  • Frame size: 70 × 56mm
  • Aspect ratio: 5:4
  • Diagonal: 89.64mm
  • Area: 3920mm2
  • Unperforated
  • Double the length of 120 roll film

Shutter speed ring with "F" setting

The "F" setting disengages the leaf shutter and is set when using only the focal plane shutter in the camera body.

Catch for disengaging cross-coupling

The shutter and diaphragm settings are cross-coupled so that the diaphragm opens to a corresponding degree when faster shutter speeds are selected. The cross-coupling can be disengaged at the press of a catch.

Cross-coupling button

With the cross-coupling button depressed speed/aperture combinations can be altered without changing the Exposure Value setting.

M & X sync

The shutter is fully synchronized for M- and X-settings so that you can work with flash at all shutter speeds.

In M-sync, the shutter closes the flash-firing circuit slightly before it is fully open to catch the flash at maximum intensity. The M-setting is used for Class M flash bulbs.

In X-sync, the flash takes place when the shutter is fully opened. The X-setting is used for electronic flash.

X sync

The shutter is fully synchronized for X-setting so that you can work with flash at all shutter speeds.

In X-sync, the flash takes place when the shutter is fully opened. The X-setting is used for electronic flash.

MF

Sorry, no additional information is available.

Aspherical elements

Aspherical elements (ASPH, XA, XGM) are used in wide-angle lenses for correction of distortion and in large-aperture lenses for correction of spherical aberration, astigmatism and coma, thus ensuring excellent sharpness and contrast even at fully open aperture. The effect of the aspherical element is determined by its position within the optical formula: the more the aspherical element moves away from the aperture stop, the more it influences distortion; close to the aperture stop it can be particularly used to correct spherical aberration. Aspherical element can substitute one or several regular spherical elements to achieve similar or better optical results, which allows to develop more compact and lightweight lenses.

Use of aspherical elements has its downsides: it leads to non-uniform rendering of out-of-focus highlights. This effect usually appears as "onion-like" texture of concentric rings or "wooly-like" texture and is caused by very slight defects in the surface of aspherical element. It is difficult to predict such effect, but usually it occurs when the highlights are small enough and far enough out of focus.

Low dispersion elements

Low dispersion elements (ED, LD, SD, UD etc) minimize chromatic aberrations and ensure excellent sharpness and contrast even at fully open aperture. This type of glass exhibits low refractive index, low dispersion, and exceptional partial dispersion characteristics compared to standard optical glass. Two lenses made of low dispersion glass offer almost the same performance as one fluorite lens.

Low dispersion elements

Low dispersion elements (ED, LD, SD, UD etc) minimize chromatic aberrations and ensure excellent sharpness and contrast even at fully open aperture. This type of glass exhibits low refractive index, low dispersion, and exceptional partial dispersion characteristics compared to standard optical glass. Two lenses made of low dispersion glass offer almost the same performance as one fluorite lens.

Canon's Super UD, Nikon's Super ED, Pentax' Super ED, Sigma's FLD ("F" Low Dispersion), Sony' Super ED and Tamron's XLD glasses are the highest level low dispersion glasses available with extremely high light transmission. These optical glasses have a performance equal to fluorite glass.

High-refraction low-dispersion elements

High-refraction low-dispersion elements (HLD) minimize chromatic aberrations and ensure excellent sharpness and contrast even at fully open aperture.

High Index, High Dispersion elements

High Index, High Dispersion elements (HID) minimize chromatic aberrations and ensure excellent sharpness and contrast even at fully open aperture.

Anomalous partial dispersion elements

Anomalous partial dispersion elements (AD) minimize chromatic aberrations and ensure excellent sharpness and contrast even at fully open aperture.

Fluorite elements

Synthetic fluorite elements (FL) minimize chromatic aberrations and ensure excellent sharpness and contrast even at fully open aperture. Compared with optical glass, fluorite lenses have a considerably lower refraction index, low dispersion and extraordinary partial dispersion, and high transmission of infrared and ultraviolet light. They are also significantly lighter than optical glass.

According to Nikon, fluorite easily cracks and is sensitive to temperature changes that can adversely affect focusing by altering the lens' refractive index. To avoid this, Canon, as the manufacturer most widely using fluorite in its telephoto lenses, never uses fluorite in the front and rear lens elements, and the white coating is applied to the lens barrels to reflect light and prevent the lens from overheating.

Short-wavelength refractive elements

High and specialized-dispersion elements (SR) refract light with wavelengths shorter than that of blue to achieve highly precise chromatic aberration compensation. This technology also results in smaller and lighter lenses.

Blue Spectrum Refractive Optics

Organic Blue Spectrum Refractive Optics material (BR Optics) placed between convex and concave elements made from conventional optical glass provides more efficient correction of longitudinal chromatic aberrations in comparison with conventional technology.

Diffraction elements

Diffraction elements (DO, PF) cancel chromatic aberrations at various wavelengths. This technology results in smaller and lighter lenses in comparison with traditional designs with no compromise in image quality.

High refractive index elements

High refractive index elements (HR, HRI, XR etc) minimize field curvature and spherical aberration. High refractive index element can substitute one or several regular elements to achieve similar or better optical results, which allows to develop more compact and lightweight lenses.

Apodization element

Apodization element (APD) is in fact a radial gradient filter. It practically does not change the characteristics of light beam passing through its central part but absorbs the light at the periphery. It sort of softens the edges of the aperture making the transition from foreground to background zone very smooth and results in very attractive, natural looking and silky smooth bokeh.

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You are already on the page dedicated to this lens.

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Cannot compare the lens to itself.

Image stabilizer

A technology used for reducing or even eliminating the effects of camera shake. Gyro sensors inside the lens detect camera shake and pass the data to a microcomputer. Then an image stabilization group of elements controlled by the microcomputer moves inside the lens and compensates camera shake in order to keep the image static on the imaging sensor or film.

The technology allows to increase the shutter speed by several stops and shoot handheld in such lighting conditions and at such focal lengths where without image stabilizer you have to use tripod, decrease the shutter speed and/or increase the ISO setting which can lead to blurry and noisy images.

Original name

Lens name as indicated on the lens barrel (usually on the front ring). With lenses from film era, may vary slightly from batch to batch.

Format

Format refers to the shape and size of film or image sensor.

35mm is the common name of the 36x24mm film format or image sensor format. It has an aspect ratio of 3:2, and a diagonal measurement of approximately 43mm. The name originates with the total width of the 135 film which was the primary medium of the format prior to the invention of the full frame digital SLR. Historically the 35mm format was sometimes called small format to distinguish it from the medium and large formats.

APS-C is an image sensor format approximately equivalent in size to the film negatives of 25.1x16.7mm with an aspect ratio of 3:2.

Medium format is a film format or image sensor format larger than 36x24mm (35mm) but smaller than 4x5in (large format).

Angle of view

Angle of view describes the angular extent of a given scene that is imaged by a camera. It is used interchangeably with the more general term field of view.

As the focal length changes, the angle of view also changes. The shorter the focal length (eg 18mm), the wider the angle of view. Conversely, the longer the focal length (eg 55mm), the smaller the angle of view.

A camera's angle of view depends not only on the lens, but also on the sensor. Imaging sensors are sometimes smaller than 35mm film frame, and this causes the lens to have a narrower angle of view than with 35mm film, by a certain factor for each sensor (called the crop factor).

This website does not use the angles of view provided by lens manufacturers, but calculates them automatically by the following formula: 114.6 * arctan (21.622 / CF * FL),

where:

CF – crop-factor of a sensor,
FL – focal length of a lens.

Mount

A lens mount is an interface — mechanical and often also electrical — between a camera body and a lens.

A lens mount may be a screw-threaded type, a bayonet-type, or a breech-lock type. Modern camera lens mounts are of the bayonet type, because the bayonet mechanism precisely aligns mechanical and electrical features between lens and body, unlike screw-threaded mounts.

Lens mounts of competing manufacturers (Canon, Nikon, Pentax, Sony etc.) are always incompatible. In addition to the mechanical and electrical interface variations, the flange focal distance can also be different.

The flange focal distance (FFD) is the distance from the mechanical rear end surface of the lens mount to the focal plane.

Lens construction

Lens construction – a specific arrangement of elements and groups that make up the optical design, including type and size of elements, type of used materials etc.

Element - an individual piece of glass which makes up one component of a photographic lens. Photographic lenses are nearly always built up of multiple such elements.

Group – a cemented together pieces of glass which form a single unit or an individual piece of glass. The advantage is that there is no glass-air surfaces between cemented together pieces of glass, which reduces reflections.

Focal length

The focal length is the factor that determines the size of the image reproduced on the focal plane, picture angle which covers the area of the subject to be photographed, depth of field, etc.

Speed

The largest opening or stop at which a lens can be used is referred to as the speed of the lens. The larger the maximum aperture is, the faster the lens is considered to be. Lenses that offer a large maximum aperture are commonly referred to as fast lenses, and lenses with smaller maximum aperture are regarded as slow.

In low-light situations, having a wider maximum aperture means that you can shoot at a faster shutter speed or work at a lower ISO, or both.

Floating element system

Provides correction of aberrations and ensures constantly high image quality at the entire range of focusing distances from infinity down to the closest focusing distance. It is particularly effective for the correction of field curvature that tends to occur with large-aperture, wide-angle lenses when shooting at close ranges.

The basic mechanism of the floating element system is also incorporated into the internal and rear focusing methods.

Closest focusing distance

The minimum distance from the focal plane (film or sensor) to the subject where the lens is still able to focus.

Closest working distance

The distance from the front edge of the lens to the subject at the maximum magnification.

Magnification ratio

Determines how large the subject will appear in the final image. Magnification is expressed as a ratio. For example, a magnification ratio of 1:1 means that the image of the subject formed on the film or sensor will be the same size as the subject in real life. For this reason, a 1:1 ratio is often called "life-size".

Manual diaphragm

The diaphragm must be stopped down manually by rotating the detent aperture ring.

Preset diaphragm

The lens has two rings, one is for pre-setting, while the other is for normal diaphragm adjustment. The first ring must be set at the desired aperture, the second ring then should be fully opened for focusing, and turned back for stop down to the pre-set value.

Semi-automatic diaphragm

The lens features spring mechanism in the diaphragm, triggered by the shutter release, which stops down the diaphragm to the pre-set value. The spring needs to be reset manually after each exposure to re-open diaphragm to its maximum value.

Automatic diaphragm

The camera automatically closes the diaphragm down during the shutter operation. On completion of the exposure, the diaphragm re-opens to its maximum value.

Fixed diaphragm

The aperture setting is fixed at F/1.2 on this lens, and cannot be adjusted.

Number of blades

As a general rule, the more blades that are used to create the aperture opening in the lens, the rounder the out-of-focus highlights will be.

Some lenses are designed with curved diaphragm blades, so the roundness of the aperture comes not from the number of blades, but from their shape. However, the fewer blades the diaphragm has, the more difficult it is to form a circle, regardless of rounded edges.

At maximum aperture, the opening will be circular regardless of the number of blades.

Weight

Excluding case or pouch, caps and other detachable accessories (lens hood, close-up adapter, tripod adapter etc.).

Maximum diameter x Length

Excluding case or pouch, caps and other detachable accessories (lens hood, close-up adapter, tripod adapter etc.).

For lenses with collapsible design, the length is indicated for the working (retracted) state.

Weather sealing

A rubber material which is inserted in between each externally exposed part (manual focus and zoom rings, buttons, switch panels etc.) to ensure it is properly sealed against dust and moisture.

Lenses that accept front mounted filters typically do not have gaskets behind the filter mount. It is recommended to use a filter for complete weather resistance when desired.

Fluorine coating

Helps keep lenses clean by reducing the possibility of dust and dirt adhering to the lens and by facilitating cleaning should the need arise. Applied to the outer surface of the front and/or rear lens elements over multi-coatings.

Filters

Lens filters are accessories that can protect lenses from dirt and damage, enhance colors, minimize glare and reflections, and add creative effects to images.

Lens hood

A lens hood or lens shade is a device used on the end of a lens to block the sun or other light source in order to prevent glare and lens flare. Flare occurs when stray light strikes the front element of a lens and then bounces around within the lens. This stray light often comes from very bright light sources, such as the sun, bright studio lights, or a bright white background.

The geometry of the lens hood can vary from a plain cylindrical or conical section to a more complex shape, sometimes called a petal, tulip, or flower hood. This allows the lens hood to block stray light with the higher portions of the lens hood, while allowing more light into the corners of the image through the lowered portions of the hood.

Lens hoods are more prominent in long focus lenses because they have a smaller viewing angle than that of wide-angle lenses. For wide angle lenses, the length of the hood cannot be as long as those for telephoto lenses, as a longer hood would enter the wider field of view of the lens.

Lens hoods are often designed to fit onto the matching lens facing either forward, for normal use, or backwards, so that the hood may be stored with the lens without occupying much additional space. In addition, lens hoods can offer some degree of physical protection for the lens due to the hood extending farther than the lens itself.

Teleconverters

Teleconverters increase the effective focal length of lenses. They also usually maintain the closest focusing distance of lenses, thus increasing the magnification significantly. A lens combined with a teleconverter is normally smaller, lighter and cheaper than a "direct" telephoto lens of the same focal length and speed.

Teleconverters are a convenient way of enhancing telephoto capability, but it comes at a cost − reduced maximum aperture. Also, since teleconverters magnify every detail in the image, they logically also magnify residual aberrations of the lens.

Lens caps

Scratched lens surfaces can spoil the definition and contrast of even the finest lenses. Lens covers are the best and most inexpensive protection available against dust, moisture and abrasion. Safeguard lens elements - both front and rear - whenever the lens is not in use.