Canon EOS-1D X Manual (en)

You can also use this palette to adjust the image sharpness. For 
information on making adjustments, see “Adjusting Image Sharpness” in 
“Editing with the Basic Adjustment Tool Palette” 
Use the slider to adjust the Digital Lens Optimizer effect.
If no shooting distance information is saved to the image, the 
shooting distance slider is set automatically to the right end at 
infinity position and a [<!>] appears above the shooting distance 
If the lens requires no adjustment with the [Shooting distance 
information] slider, the slider cannot be used.
Images cannot be corrected for [Chromatic aberration] in the lens 
aberration correction tool pallet if the Digital Lens Optimizer has 
been applied.
In the main window, the [
mark is displayed on the image to 
indicate that the Digital Lens Optimizer is applied
Adjusting Image Sharpness