Canon EF600mm f/4L IS III USM Instructions Manual page 14

Focus Preset
When setting two presets, pressing the focus preset button but then not turning the playback ring causes the
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lens to beep three times and cancel presetting. Set presets from the start again.
The camera may turn off while setting two presets. Press the shutter button halfway, and then set presets
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from the start again.
When not using focus presets, set the focus preset switch to OFF.
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With the following camera models, focus presets cannot be used with Live View shooting or movie shooting.
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EOS 60Da, EOS REBEL T5/1200D, EOS REBEL T6/1300D, EOS REBEL T7/2000D/1500D, EOS REBEL
T100/4000D/3000D
As well as all EOS cameras released in 2011 and earlier
Focus presets can be used in all focus modes. Focus speed is slow only during movie shooting when the
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focus mode is PF, and is fast for all other settings. In slow speed, you can make a 2-step change in focus
speed depending on how much the playback ring is turned.
All focus presets are initially at the lens' mechanical limit in the infinity direction (not at infinity) when the lens
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is mounted on a camera.
Preset focusing distances remain in memory until the lens is detached from the camera.
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ENG-13