Canon EOS 50 E - Page 67

Part 2: Technical Information
11) Calculation of main flash output
The E-TI'L system's algorithm calculates the main flash output according ton-
times the preflash output. The result is sent to the 380 EX.
START
Since the subject is covered by the focusing
point and it gives the greatest reflected light,
the corresponding sensor controls the main
flash output to obtain correct exposure.
No
Yes
Since manual focus is used, or the framing
has been changed, the subject may no
~--------l.i longer be covered by the same focusing
No
point. Therefore, the sensor (SO, S 1, S2,
S3, or S4) detecting the brightest reflected
light controls the flash to obtain a correct
exposure.
If the framing has not been changed, the camera can assume that the
subject is still covered by the same focusing point. However,
since it does not match up with the brightest reflected light area,
the sensor corresponding to the focusing point which achieved
focus seeks a correct exposure while the other sensors having a
focusing point seek overexposure by one stop. The main flash
output is controlled by the first sensor to reach its correct
exposure point.
Fig. 2-18 E- 'ITL Autoftash Algorithm Diagram
12) Exposure control.
13) Operation completion.
4) FE Lock
FE lock is AE lock for flash. The operation steps executed by the EOS 50/55/Elan II are
described below.
* The operation steps executed by the 380 EX are as described previously.
FE lock (1) sequence: Shutter button pressed halfway, pause, FE lock, and shutter but-
ton pressed completely.
■ Major operation steps executed by the EOS 50/55/Elan II:
1) Ambient light metered by the camera's metering mode.
2) Exposure control calculated by the algorithm.
*
The flash aperture and sync speed are set as described previously.
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