Canon 100-300mm F2.8 L IS USM Instructions Manual page 12

7. Focus Preset
By presetting any focusing distance, you can instantly focus at that point even while you are
shooting a different subject. This function operates both in AF and MF mode.
< Preset the Focusing Distance >
Set the lens function/focus preset selector
switch to PRESET.
Focus the lens at a focusing distance you
want to preset.
Press the lens function/focus preset button to
preset the distance in memory.
< Shoot at the Preset Focusing Distance >
Set the lens function/focus preset selector
switch to RECALL.
Press the lens function/focus preset button to
move the focus to the preset distance. Press
the shutter button while holding down the lens
function/focus preset button to shoot at that
distance.
Lens function/focus preset selector switch
Lens function/focus preset button
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