I recently aquired a lens similiar to this one "Xerox/Fuji 325mm Focal Length Multi-Element Lens", the problem I am having is that there is dust on the inside. Do I need a special tool to disassemble it or can I merely loosen the three alan screws on the sides to remove the outer lenses. I emailed where I bought it from and am awaiting an answer, but thought I might post seeing that I am anxious.