E-Ttl Flash System - Canon EOS 55 Service Manual

Part 2: Technical Information
1.6 E-TTL Flash System
An
E-TIL Flash System, which operates when the Speedlite 380EX is mounted on the
EOS 50/55/Elan II is incorporated. This E-TIL Flash System is an improved version of
the A-TIL auto flash exposure system. It features flash output control and automatic
exposure control (ambient light exposure) to balance the flash and ambient light in day-
light or at night.
The features of this E-TIL Flash System are as follows:
1. With the new evaluative flash metering system linked to the focusing points, the
camera sets the flash exposure automatically (even when the framing is changed) for
a variety of situations such as back-lit subjects, fill-flash, and indoor photography.
*
For indoor flash photography in the Full Auto or Program mode, 1/60 sec. is the
slowest synchronizing shutter speed that can be set. Therefore as with the current
flash exposure system, the background behind the subject might be underexposed.
2. High speed synchronization ( called FP flash) enables flash to be used with fast shut-
ter speeds. It allows you to open up the aperture for fill-in flash to obtain blurred
backgrounds for portraits. (Creative Zone)
3. For flash photography indoors or under low-light conditions, a slow shutter speed
will be set automatically to obtain a balanced exposure between the subject and
background. (Aperture-priority AE)
4. With FE lock (Flash Exposure lock ). proper exposure even for spotlighted subjects is
possible.
The E-TIL Flash System operates as follows: The Speedlite 380EX fires a preflash. The
camera's six-zone flash metering sensor reads the ambient light immediately before the
preflash is fired.
It
also reads the light reflected from the subject produced by the pre-
flash. The difference in the lighting of the readings is used to calculate the flash output
which is retained in memory. Table 2-8 compares the E-TIL Flash System with existing
flash control systems.
Table 2-8 Comparison of Flash Control Systems
Item E-TTL
A-TTL TTL <Built-in Flash)
Near infrared preflash X 0 X
Tv and Av
Set by brightness infor- Set by brightness infor- Set according to the
SW-1 ON
mation from the meter- mation from the meter- brightness information
(Shutter
ing sensor. ing sensor and the sub- obtained by the meter-
button
ject distance informa- ing sensor.
pressed
tion from the near
halfway)
infrared creflash.
Preflash 0 X
X
Flash output Set and held by the
ambient light and pre-
-
SW-2 ON
flash readings.
(Shutter
Start of front curtain, The main flash is fired
Main flash is fired.
button
X-sync ON
according to the calcu-
pressed
lated flash output that
completely)
was retained.
TTL-OTF metering
Flash sensor is used.
Flash termination Flash stonned when flash exoosure is orooer.
Fast Shutter Sync. (FP flash) 0 X
X
TTL flash exposure sensor
X
0
0
2-17