way to much information! ( canon lenses)


<font color=darkcoral>Right now I'm an inch of nat
Aug 16, 2003
probably way more than anyone really wants to know but this is in response to me emailing them about using my lenses with my film slr rebel.. since they answered my question in PP 2, you got to admit they were thorough:lmao: but it's interesting non the less

Thank you for contacting Canon product support. We value you as a Canon
customer and appreciate the opportunity to assist you.

The entire line of Canon EF lenses are compatible with the EOS Rebel K2.
Regrettably, the EF-S series lenses are not. I am sorry for any

A variety of lenses from third-party manufacturers - Sigma, Tokina,
Tamron, and others - are available in Canon EF mounts to fit Canon EOS
camera bodies. However, contrary to popular belief, these companies are
not "licensed" to produce these lenses; instead, their designers must
basically take apart and analyze EOS cameras and lenses, and then
"reverse-engineer" them to fit and operate on EOS camera bodies.

The Canon EF lens mount

Unlike all previous interchangeable-lens camera mounts, Canon's EF lens
mount was the first in the industry to go entirely electronic when the
first EOS 650 and 620 cameras were introduced in 1987. This innovative
mount relies completely on electronic communication between body and
lens, which takes place using the gold contacts on the camera body and
those on the lens's rear mount. In spite of numerous technological
advances Canon has introduced since 1987 (more on that in a moment),
this mount and the gold contacts have remained absolutely the same.

Lens to body communication

All Canon EF lenses have a microprocessor within the lens that provides
a number of items of information to the camera. When you turn on an EOS
camera (film or digital) the camera and lens communicate, and the camera
"knows" the lens's focal length, if it's a zoom lens the actual zoom
setting it's currently set to, and the maximum and minimum apertures,
among other things. When the camera is activated, this basic information
is transmitted to the camera body's main processor.

When the autofocus and light metering are activated by pressing the
shutter button halfway down, additional communication is carried out,
chiefly signaling the aperture control motor within the lens to stop the
diaphragm down to an amount determined by the camera (or the user, if
the camera's used in Av or Manual exposure modes), and a start signal is
sent to the lens's built-in focusing motor to begin driving the focusing
elements of the lens for autofocus. This is only a thumbnail sketch of
what occurs between body and lens. Many additional items are
communicated back and forth between the time the camera is turned on and
the moment the shutter button is fully depressed.

Evolution of the EOS system

Since the first EOS cameras and EF lenses in 1987, a number of new
technologies have been introduced into Canon's EOS system. As new camera
and/or lens features have been developed, this has added to the amount
of items communicated between body and lens. Canon has been able to do
this and maintain practically total compatibility going back to the
earliest EOS bodies and lenses. Most importantly, the lens mount and the
gold contacts have not changed one bit!

Features introduced since 1987 that have altered the way data is
communicated include:

Predictive AI Servo AF (focus tracking on moving subjects)
Micro-USMs (extremely small Ultrasonic focusing motors)
Tilt-shift lenses with Automatic Diaphragm operation
Multiple-point AF systems, from 3 points up to 45
Image Stabilization
E-TTL flash (which relies on instant analysis of a pre-flash)
Wireless E-TTL flash

Furthermore, as new cameras have been developed, new and faster
communication methods have been introduced to give us faster autofocus,
more precise light metering, faster shooting speeds (up to 9 fps, with
autofocus on the EOS-1v, for instance), and of course the new features
that digital SLRs bring to the table.

Data communication has accordingly changed over time, and occasionally a
new camera will be launched that modifies how data is transmitted
between body and lens. For example, when E-TTL was launched with the EOS
Elan II camera in 1995, its aperture stop-down communication was altered
compared to previous EOS cameras. Again, all Canon-made EF lenses had
processors able to accommodate the shift in data transmission, and
worked without modification.

Communication errors

Whenever an EOS camera cannot complete electronic communication with a
lens, or detects an internal disturbance, the camera is designed to
lock-up on the first attempt to fire the shutter. Usually, a
dead-battery icon blinks in the same manner as a "check engine" light in
a car. This assures that there's almost no possibility of a user
shooting an entire wedding or vacation, for instance, with a lens that's
not stopping down its aperture properly or otherwise not working with
the camera properly.

Third-party lenses

The makers of third-party accessory lenses are not given this
information when Canon introduces new features or improves the
performance of its cameras and lenses. It's up to them to continue to
"reverse-engineer" their equipment to enable it to continue to work on
new EOS bodies as they're developed. Since Canon designs our own
processors and all electronics within the body and lens, we have been
able to maintain backward compatibility. This is one of the many
advantages of choosing a Canon EF lens.

When changes in communication result in a third-party lens that now
produces errors, it's up to the makers of that lens to update the
equipment to work on the EOS camera in question. Again, Canon's own EF
lenses work without modification.

The meaning of "fully compatible"

Many third-party lenses with EF mounts are sold to customers with the
claim by store salespeople or even the lens manufacturer that they're
"fully compatible" with all Canon EOS cameras. Canon, Inc. in Japan and
Canon USA offer no rebuttal to those claims.

Any compatibility is based on the reverse engineering we described
earlier in this document. And if a user mounts this lens on a certain
Canon EOS camera and it locks up, it's up to the user to contact the
lens manufacturer (after verifying it's a lens issue; see below) and
tell the lens maker's service department, "make it right."

If a user encounters lock-ups

The easiest thing to do is to remove the battery for a moment, and
re-install it, which gives the camera the chance to perform an internal
electronic re-set. Try mounting a Canon brand lens on the camera (even
if it's a dealer's demo lens off the shelf) and fire it to see if you
can repeat the problem. If lock-ups only occur with a third-party lens,
it's a pretty safe bet that it's the lens that must somehow be modified
or adjusted. If, on the other hand, the camera continues to lock up with
a Canon-brand lens mounted, then it's likely that something else is
wrong with the camera and it should be sent to a qualified repair
technician or a Canon Factory Service Center for examination.

Sigma information on-line

Sigma, a large maker of third-party lenses for various SLR cameras, has
been up-front with this issue, and frequently announces updates for
Sigma lens owners on their web site (www.sigmaphoto.com). As of
mid-August, 2003, there's an item in their "News" section of the web
site under the heading, "Important Notice For Canon EOS 10D and Canon
Elan 7/Elan 7e camera Users", which outlines exactly this need for
certain models of their lenses made prior to a certain date to be sent
to them for modification. In this instance, Sigma is performing this
upgrading of affected lenses at no charge. Of course, it's entirely up
to the lens maker whether or not they will charge a fee for any
upgrading service performed on one of their lenses.

Other lens manufacturers from time to time post similar information;
it's up to owners of these lenses to check the maker's web site or
contact their service department if and when any errors resulting in
lock-ups occur.

We hope this information is helpful to you. Please feel free to contact
us again if you have any other questions or concerns with the EOS Rebel

Thank you for choosing Canon.


Technical Support Representative


I may not have gone where I intended to go, but I
Mar 5, 2006
On another thread you mentioned that the microprocessor/motherboard on your 28-135 IS lens went bad and that you were going to stay away from IS lenses. After reading this, it sounds like all EF lenses have that microprocessor/motherboard, not just IS.

Does that change your opinion on IS lenses at all? This article doesn't make me rethink IS lenses, but it does make me rethink 3rd party lenses (which was probably their objective).


<font color=darkcoral>Right now I'm an inch of nat
Aug 16, 2003
yeah funny how they didn't encourage me to run out and buy a sigma:lmao:
they may have covered 3 party though as i mentioned all the lenses i have and i have 1 that is 3rd party. i wondered about the motherboard also and if it's the same motherboard, could it be more than one? if it was the same that might explain why it didn't focus period. i still don't know about is....i haven't really heard a lot of complaints on photo forums so don't know if since mine is the old is if maybe it was an upgrade they needed to do ie a bug of some kind or what.i've been happy with the photos with the 28-135 but not really sure if it's the is or just the lens is better than the ones i had before or if the is really helps with my tremors...i guess i will find out when i get the 70-200 and try the 200 end...so far with my 100 and 50 lenses i haven't really had a problem but my tremors haven't been that bad either lately. so who knows!:rotfl: