Pentax K-X Operating Manual page 69

Dust Alert is the function that detects dust adhering to the CMOS sensor
and visually displays the location of the dust.
You can save the detected image and display it when performing sensor
cleaning (p.287).
The following conditions must be met before using the Dust Alert function:
- A DA, DA L, FA J lens or a D FA, FA and F lens that has an Aperture
A (Auto) position is attached.
- The aperture is set to the A position when using a lens with an
aperture ring.
- The mode dial is set to any mode other than p_ (Movie).
- The focus mode lever is set to AF.
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2
3
Select [Dust Alert] in the [_ Set-up 4] menu and press the
four-way controller (•).
The [Dust Alert] screen appears.
Fully display a white wall or
uniformly bright subject in the
viewfinder and press the shutter
release button fully.
After image processing is performed, the
Dust Alert image appears.
If the message [The operation could not
be completed correctly] is displayed,
press the OK button and take another picture.
Dust Alert
Checks for dust on the sensor
Press shutter release button
to reveal dust location
Press the
OK
button.
The image is saved and the camera
returns to the [& Set-up 4] menu.