CANON EOS FAQ Version 2.4
All original material is Copyright © 1992, 1993, 1994, 1995 Alvin
Chia-Hua Shih and Robert M. Atkins.
Date: November 1993
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- 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
- 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
- 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
- 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
- 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
ACS & RMA
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
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 ** **
** 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
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