thank you Tim, now I know how to set the aperture manually. In my case (using the Canon's RF mount) I simply do the following:
- With the lens attached to the Canon R5 and the camera powered on I set the aperture to f3.5
- I do not switch off the camera
- I remove the lens from the Canon R5 (Canon advises against doing this as the sensor is unprotected with the Camera powered and the lens removed)
- The lens keeps the aperture of f3.5 after it was removed from the camera body

Needless to say, I remove the lens very carefully and cover the sensor immediately with the cap.

Regards
Thomas

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