If you are having problems with binding then you probably have the wrong zoom ring or lens clamp installed. attached you will see two zoom rings and two lens clamps. The zoom rings to the left are for smaller diameter lenses and have a taller bar on them then the ones on the right. the lens clamps on the right are different thicknesses also. Feel free to mix and mach as needed. When they are installed they should be snug but not binding. also don't forget that the rubber gripers for the clamps if needed.
I am sure that this will solve your problems.
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