Canon EF 400mm f/2.8L IS USM Benutzerhandbuch (en)

See your camera’s instructions for details on
mounting and detaching the lens.
1. Mounting and Detaching the Lens
After detaching the lens, place the lens with the
rear end up to prevent the lens surface and
contacts from getting scratched.
If the contacts get soiled, scratched, or have
fingerprints on them, corrosion or faulty
connections can result. The camera and lens
may not operate properly. 
If the contacts get soiled or have fingerprints on
them, clean them with a soft cloth.
If you remove the lens, cover it with the dust
cap. To attach it properly, align the lens mount
index and the 
 index of the dust cap as shown
in the diagram, and turn clockwise. To remove it,
reverse the order.
The lens mount has a rubber ring for enhanced
dust- and water-resistance. The rubber ring may
cause slight abrasions around the camera’s lens
mount, but this will not cause any problems. If the
rubber ring becomes worn, it is replaceable by a
Canon Service Center at cost.
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