While withdrawing the forward lens assembly, turn the focus helicoid counter clockwise to
remove the forward tube and focusing group cell. place in a safe place to prevent damage.
It is recommended that a front lenscap be kept on the lens at all times during repair as access to the front element is not required for all repairs except to the front element group.

For cleaning of the front focus cell, see the 70-210mm gallery, as they are similar.

Upon reassembly, carefully thread the helicoid back together. Check to see that the distance scale
is visible in the focus scale window to the full extent of its range. If not, turn out the helicoid counter clockwise until the next thread engages. Turn in and check the focus window. Repeat until in the correct position.

Note pile dust seal around front edge of forward tube, there is another inside the focus ring. Clean and restore the nap with a damp toothbrush.