III. FEATURE DISCUSSION 8
T
he removed dust then sticks to an absorbent material ringing the low-pass filter. The
s
ensor unit also has an internal O-ring around the perimeter to keep out dust. The area
b
etween LPF #1 and the CMOS sensor is thus sealed; dust cannot enter from the side.
I
nstead of a dust-removal system which uses a vibrating
g
lass, the Digital Rebel XTi uses its low-pass filter to
v
ibrate directly, shaking off dust. Therefore, the optical
performance is not degraded by an extra sheet of glass,
and compactness is maintained. The camera body size is
virtually the same as that of the Digital Rebel XT.
The default setting for the self-cleaning sensor has the
cleaning unit operating for 1 sec. when the camera's
power switch is turned on or off. Dust is therefore
removed before shooting and after shooting is completed,
the latter instance because dust is more difficult to dis-
lodge after it has been stuck for a long time. Self-cleaning
can be enabled or disabled by setting "Clean when the power switch is turned <ON> or
<OFF>" to [Enable] or [Disable]. During self-cleaning operation, the LCD screen displays an
appropriate self-cleaning system logo.
The self
-cleaning system can also be activated manually with the menu item [Clean
now]. Note that shooting priority still holds. If you press the shutter button halfway or
press the menu button during the self- cleaning operation (in either the Auto or Manual
modes), the cleaning operation will stop and the camera will be ready to shoot.
Pressing the shutter button during the internal processing startup sequence (immedi-
ately after the 0.2 second startup) will make shooting possible at that moment and sen-
sor cleaning will not occur.
During manual cleaning with the reflex mirror locked up, the LCD screen will indicate
that sensor cleaning is in progress. When the battery level is low, the following warn-
ings are given: First, the beeper will sound even if [Beep] is set to [Off]. Second, a warn-
ing message is displayed on the LCD screen until the prohibited voltage is reached.
Because the self-cleaning system requires exceptionally
low power, the number of possible shots from a charged
battery is not reduced measurably.
To prevent the piezoelectric element from overheating,
the self-cleaning unit cannot operate for 3 sec. after any
CMOS
sensor
Phaser layer
Infrared-absorbing glass
Low-pass filter 2
O-ring
Support material
Piezoelectric
element
Low-pass filter 1
Self Cleaning Sensor Unit
ON
Startup
0.2 sec.
Internal processing
0.5 to 2 seconds
Sensor cleaning
Approximately 1 second
Shooting is possible immediately after startup
Cleaning complete
