Canon EF Lenses Manual - Page 20

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Large, Fully Electronic

Mount System

Focus Preset

The conventional interface between the

With the focus preset feature, you can

lens and camera body was mechanical,

set the desired focusing distance in

with the use of engaging levers and gears.

This method caused physical problems

memory and later instantly focus the lens

at that distance. Normal picture-taking

such as wear and rattle. It was limited

and focusing are possible even while

and more diverse information could not

focus preset has been set. At a soccer

be exchanged. Canon EF lenses do not

game, for example, you can preset the

use such mechanical links at all. About

focus for the goal. You can focus normally

50 items of information are exchanged

while the player approaches the goal,

as digital signals between the lens and

then when the ball is shot into the goal,

camera in real time. This enables high-

you can obtain instant focus.

speed and high-precision control. And

since the lens mount diameter is an

ample 54 mm, special lenses such as

large-aperture lenses and TS-E lenses

can be used. The EF mount is an

advanced interfacing system with

Fluorite (CaF2) and UD-Glass

infinite possibilities.

The refraction of light differs depending

on the wavelength. The point of focus

Built-In Motor and EMD

therefore differs depending on the

different wavelengths or colors. When

Canon EF lenses (except TS-E and

the different wavelengths are focused

MP-E lenses) have a built-in AF motor.

Compared to camera body-based AF

at different points, the colors look

smeared. This is called chromatic

motors, lens-based motors have driving

aberration. The longer the focal length,

energy with lower transmission loss.

the more pronounced chromatic aberration

The optimum AF motor for the particular

becomes. Usually, an achromatic

lens can also be selected and installed.

element is used in a lens to correct

The AF operation is therefore quick, quiet,

chromatic aberration. However, normal

and highly precise. The lenses also have

optical glass can only be corrected for

an EMD (Electromagnetic Diaphragm) to

two primary spectral colors. An exception

control the aperture electronically. The

to this limitation is Fluorite, an ideal

aperture can be set either with an

material. Fluorite, which is crystalline,

electronic dial or with the electronic pulse

has abnormally low refraction and low

signal sent according to the exposure

dispersion characteristics, which optical

reading. Aperture control precision is

glass cannot achieve. It also has

therefore unmatched.

anomalous dispersion from the green

to blue wavelengths. Canon developed

Ring-type USM

production technologies to manufacture

Fluorite. By incorporating Fluorite in

lenses, the points of focus of the three

primary spectral colors of red, green,

and blue all meet at one point for ideal

correction of chromatic aberration. There

is also UD-glass, which is a special type

of optical glass whose properties nearly

EMD

match those of Fluorite. The effect of

two UD-glass elements is equivalent to

Built-in motor and EMD

having one Fluorite element. And one

super UD-glass element gives almost

the same effect as one Fluorite element.

Inner Focusing and

Comparison of optical characteristics

between optical glass and Fluorite

Rear Focusing

An inner focusing lens has the focusing

lens group(s) in front of the diaphragm,

Red

while a rear focusing lens has the focus-

ing lens group(s) behind the diaphragm.

Glass

Blue

Both focusing systems allow the focusing

lens group to be small. This minimizes

Anomalous

the load on the actuator which drives

dispersion

the autofocus. In turn, the AF speed is

faster. The whole optical system can also

Red

be made more compact. Also, since the

Blue

lens does not rotate during focusing,

Fluorite

the effects of a circular polarizing filter

or gelatin filter remain intact.

Fluorite and UD glass

Description of Lens Designation

The lens designations follow a standard format to identify the lens.

EF 75-300mm f/4-5.6 IS USM

Focal length:

Maximum aperture:

Special Function:

Indicates the focal

Indicates the lens'

Any special

length range from

maximum aperture.

feature such as an

the shortest to

(See below for

image stabilizer,

longest length.

details.)

macro feature, etc.,

(See below for

is indicated.

details.)

Focal Length

two, one for each end of the focal

A focal length of 50mm is closest to

length range. For example, a EF 28-80mm

what the eye sees. This focal length is

f/3.5-5.6 lens has a maximum aperture

used as a reference point for lens

of f/3.5 at 28mm and f/5.6 at 80mm.

categories. For example, lenses with a

shorter focal length are called wide-angle

Aperture and Shutter Speed

lenses, while those with a longer focal

Under the same light level, if the

length are called telephoto lenses.

aperture opening is made larger by one

Single focal length lenses have only one

step, the shutter speed can be increased

focal length, while zoom lenses have a

by one step. For example, if an aperture

range of focal lengths. (When EF lenses

of f/5.6 and shutter speed of 1/60 sec.

are used with the EOS IX, the focal

are set, adjusting the aperture to f/4 will

length corresponds to 1.25 times that

enable a shutter speed of 1/125 sec. to

indicated for 35mm cameras.)

be used. An aperture of f/2.8 will allow

a faster shutter speed of 1/250 sec. while

Angle of View

the same exposure level is maintained.

This indicates how much coverage of

the scene you can see through the lens.

Depth of Field

Telephoto lenses have a narrower angle

Normally, there is only one point of

of view than wide-angle lenses.

optimum focus. However, we often see

objects in front of or behind this point

Angle of View and Perspective

also in focus. This is made possible by

Perspective refers to the distance

a wide depth of field.

between the near and far objects that

you can see at the same time. When the

Depth of Field with the

angle of view is wide (with a shorter focal

Aperture and Focal Length

length), the perspective becomes more

apparent. And with a narrow angle of

The depth of field is mainly determined

view (with a longer focal length), the

by the lens focal length, aperture, and

perspective becomes less apparent. The

subject distance. For example, if a wide-

image also becomes more compressed,

angle lens is used at the minimum

with the far objects looking like they are

aperture, almost everything in the picture

right behind the nearer objects.

will be in focus. However, if a telephoto

lens is used at maximum aperture, the

background will be really blurred, making

Maximum Aperture

the subject in focus stand out.

This indicates the speed of the lens. A

fast lens has a large maximum aperture,

allowing more light to enter. The smaller

the maximum aperture's f-number, the

larger the aperture opening is. A larger

maximum aperture makes the image

look brighter and easier to see through

the viewfinder. You can also use a

faster shutter speed or obtain better

background blur. On the other hand, a

smaller maximum aperture (the f-number

is larger) allows the lens to be more

compact and light. Single focal length

lenses have only one maximum

aperture while zoom lenses may have

Canon EF Lens Accessories

General Purpose Filters for Black and

White or Color Film

Sky (1A), Haze (UV-1), ND (03 • 0.6)

• 52mm • 58mm • 72mm

Conversion Filters for Color Film

USM: Indicates

80A, 80B, 85, 85B, FCB, FCD

that the lens uses

• 52mm • 58mm • 72mm

an Ultrasonic

Motor for

General Purpose Filters for Black

autofocusing.

and White Film

(See page 34 for

Yellow 2, Green 11, Orange 15, Red 25A

details.)

• 52mm • 58mm • 72mm

Softmat Filters

Softmat filters mildly soften the focus for

flattering portraits and dreamy landscapes.

These filters utilize the effect of diffraction which

occurs between light passing through the

transparent part and light passing through the

coated part. Use Softmat No. 1 filter for a gentle

softfocus effect, and Softmat No. 2 for a

stronger effect.

No.1, No.2

• 52mm • 58mm

Warming Filters for Color Film

81A, 81B

• 52mm • 58mm • 72mm

Circular Polarizing Filters PL-C

Polarizing filter enhances picture quality by

blocking harmful reflected light. Use it to

reduce polarized light reflections from glass

and water surfaces or to improve color satura-

tion. Simple to use, circular polarizing filters

(such as Canon's PL-C) polarize light circularly,

rather than linearly, so it does not interfere

with autofocus or TTL light metering.

• 52mm • 58mm • 67mm • 72mm • 77mm

(Type II)

Loupe 8x & 4x

The Canon Loupe 4x is a high-performance

magnifier for viewing the entire picture area

(24 x 36mm) of a 35mm-format slide or nega-

tive. With three lens elements in three groups,

chromatic aberration and distortion are effec-

tively corrected to give crystal-clear images.

Eye fatigue is not a problem even after pro-

longed use. Loupe 8x is another magnifier for

viewing the entire picture area, but with spe-

cial emphasis on a 24mm-diameter area at the

center. The four lens elements in four groups

attain high performance and a high magnifica-

tion. All elements have Super Spectra Coating

to make image viewing clear enough for you to

effectively check the quality of photos taken

with EF lenses. These two loupes can make

your evaluation of photos more accurate.

Drop-in Filters

Drop-in Filters PL-C

Drop-in Filters PL-C can be

rotated from the outside

without removing them from

the lens for precise control.

The 48mm PL-C filter can be

used with the following lens-

es – EF 200mm f/1.8L USM

and EF 1200mm f/5.6L USM;

the 52mm PL-C filter is

designed for use with the

EF 300mm f/2.8L IS USM,

EF400mm f/2.8L IS USM,

EF 500mm f/4L IS USM and

EF 600mm f/4L IS USM.

Drop-in Gelatin Filter

Holders

These glass-backed

holders accept up to three

commercially available cut-

to-size gelatin filters for

rear-insertion lenses. A 48mm

holder is provided standard

with EF 200mm f/1.8L USM

and EF 1200mm f/5.6L USM;

and a 52mm holder, with

EF 300mm f/2.8L IS USM,

EF 400mm f/2.8L IS USM,

EF 500mm f/4L IS USM and

EF 600mm f/4L IS USM.

Drop-in Screw Filter

Holders With Protect

Filters

The enclosed regular filter

can be exchanged with other

commercially available screw-

type filters. Note that only

filters with correct filter frame

thickness can be mounted

on the lens.

• 48mm • 52mm

Only Canon filters are guaranteed for use

with EF lenses.

Gelatin filter Holders III & IV

Gelatin Filter

Holder III

Holder IV

Gelatin Filter Holder III uses 3 x 3-inch gelatin

filters and Gelatin Filter Holder IV uses 4 x 4-

inch gelatin filters. Holders III and IV both

provide extension hoods and ø52 mm, 58 mm,

67 mm, 72 mm and 77 mm adapters. Refer to

the EF Lens Accessory Table for information on

lens combinations.

• 52mm • 58mm • 67mm • 72mm • 77mm

• Adapter III for EF 50mm 1: 1.4