CANON EOS FAQ Version 2.4
Date: November 1993

2. Nomenclature:

Acronyms:

EOS: Electro-Optical System.

Canon's designation for the line of cameras which control their lenses strictly electronically. That is to say, aperture and focus are controlled by motors in the lens itself, rather than in the camera body.

EF: Electro-Focus.

The designation for lenses that are compatible with EOS bodies.

AFD: Arc-Form Drive.

The electro-mechanical assembly used to focus some of Canon's older EF lenses. It contains a small DC motor and transmission housed in an assembly shaped like an arc. These motors are audible to the human ear, in contrast to USM-driven lenses.

EMD: Electro-Magnetic Diaphragm.

The electro-mechanical assembly found in every EF lens that is used to control the aperture. This assembly includes a small motor to avoid the necessity for a mechanical control linkage to the camera body.

USM: Ultrasonic Motor.

A type of motor used in more recent EF lenses. It is inaudible to the human ear, but it has been reported to disturb cats. There are two variants: ring-shaped and "micro". The ring shaped motor is found in Canon's higher-end USM lenses. It boasts high torque and does not require any form of transmission gearing. The "Micro-USM" is cylindrical, much cheaper to manufacture, but requires some form of transmission.

MM: Micro Motor.

Simply a designation for a small motor that may be used to focus a lens.

A-TTL: "Advanced" TTL.

Flash uses a 1/20th strength preflash (IR in direct mode, visible light in bounce mode) to determine how much light is added to a scene by the flash and how far down the aperture can be stopped while still providing adequate exposure with the flash. This aperture is compared with the aperture that would be selected by normal Program mode (within the constraints of the body's flash sync speed and lens' widest available aperture). The smaller of the two apertures is selected. When the shutter button is fully depressed, the flash fires and is quenched using the TTL flash circuitry.

TTL: Through-the-lens.

Often used to refer to the metering system in an SLR camera where exposure is determined through the lens and not by some external light meter. Also used as in "TTL flash metering".

OTF: Off-the-film.

An exposure mode where the light reflected off the film is used to determine the exposure, especially when taking pictures using flash.

CF: Custom Function.

These are actually user-set parameters rather than functions.:-) They allow the user to set various handling characteristics of the camera,, such as which buttons do what and whether or not to leave the film leader out after rewind. The CFs vary from camera to camera. Not all cameras have all possible CFs.

QCD: Quick Control Dial.

The dial found at the back of the EOS 1, Elan, and A2 camera bodies. It is used to control exposure compensation or aperture without the need to press a "shift" key in conjunction with the main input dial.

PIC: Programmed Image Control.

Briefly, this is Canon's term for program modes outside of the standard P, Av, and Tv. PIC modes attempt to give effects desirable in certain situations. Typical PIC modes are: landscape, macro, portrait, and sport.

UD: Ultra-low Dispersion.

A special type of optical glass which controls the amount of "dispersion" of light rays into their spectral components. This glass is useful in controlling chromatic aberrations.

FL: Fluorite.

A crystal of calcium fluoride. Extremely low dispersion. Even better than UD glass for controlling chromatic aberrations. Note that fluorite is not a "glass" by the strict definition of the term. It is a crystal. It has a very low index of refraction (1.4) and is not affected by moisture. Fluorite may be attacked by solutions of ammonium salts, so don't clean your lenses with household "glass cleaners" (which may contain ammonia)! Fluorite lens elements are not usually exposed, so you probably can't get at them anyway. Fluorite lens elements may also be a little more shock sensitive than regular "glass", but fluorite element lenses do not seem to be fragile, even under the treatment given out by some "pros", so it's probably not worth worrying about.

ACS & RMA

Model Number Equivalencies:

Canon, like many other Japanese camera companies, uses different model numbers for the same (or very similar) camera bodies, depending on the country in which the camera is to be sold. The following equivalence chart was provided by Mike Coren and Chuck Westfall:

North America       European            Japanese

1                   1                   1
10s                 10                  10 QD
Elan                100                 100 QD
**                  500                 Kiss
630                 600                 630
Rebel               1000                **
Rebel S             1000 F              1000 QD
Rebel II            1000 N              **
Rebel S II          1000 FN             1000 S
A2E                 5                   5 Quartz Date
A2                  **                  **

Notes:
** indicates that a model is (was) not available in that market
at the time of this FAQ
QD indicates a quartz date back 

Note that the 630 is the 600 in Europe, but still the 630 elsewhere. There are some differences between the North American and International models. In the U.S., Pentax (I believe) holds a patent on body-integral flash units that pop up automatically when more illumination is required. Therefore, the EOS 10s and Elan do not have this feature and require the user to press a button when an indicator illuminates in the viewfinder.

The EOS 5 differs from the A2E in that the manual mode of the EOS 5 features a metering scale of +/-2 stops in half stops, akin to the EOS 1 (which has +/- 3 stops in 1/3 stops). The A2E only has "+" and "-", over and under, exposure indicators that do not indicate the actual deviation from the camera's metered exposure. Patent issues are often cited as the reason for this difference, though it should be noted that the original Rebel also has the analog metering scale in the North American version (as well as the EOS-1), so maybe there is more to this than a simple patent problem.

One may be able to find the non-North American versions at "grey market" dealers. However it may be difficult to get some kinds of warranty service on international models. Check with Canon before purchasing a international model if you want to be sure. There should be no problem with warranty service on "North American" grey market cameras, but you might want to check with Canon before purchase just in case they change their policy or some particular model has warranty repair problems (see section 9.21).

ACS & RMA

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