Stelos 800 L is equipped with a locking slider on the right side of the housing. By fixing it in the rearmost position, use both hands to remove or replace the light shaper safely and in a controlled manner.         

(illustrative example)

    
To remove the light shaper, turn it in one direction until it stops. Pull the locking slider back with one finger until it stops and press the small locking pin down to the rear position. The slider will now remain in this position. Continue turning the light shaper in the same direction until it is unlocked. You can now carefully remove it. Please take care not to damage or scratch the protective glass.

Attaching light shapers is also very easy:
Guide the light shaper from the front onto the Stelos 800 L, align it with the bayonet recesses (small to small and large to large), push it back until it stops and then release the lock by turning it slightly to the left or right. You will hear a "click". The light shaper is now securely attached.