Lee Filters LEE 100 System Instructions page 5

To remove the polariser (again, off camera and flat in the hand is
recommended) simply push the clip hard with the ball of your thumb – on
one side only – while steadying the unit with your fingers on the other clip.
You do not need to squeeze both clips.
Once disengaged, the polariser will come away from the holder easily.
The action is quite stiff, as this prevents accidental separation when the
filter is in use.
Please note that after a few initial actions, the two components will bed in
and become much more positive in operation. Always check the polariser is
securely fixed in place before use, to be on the safe side.
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