One of the lenses I service (Olympus 75-150 f4 zoom) has a regular problem with element separation. When I look to the center of the lens (where I know the element is) I see what looks like either a hair inside the element or a circle inside the element, like a big bubble. The area inside the circle is still glued together, the area outside has "popped" or is not glued. When this lens is separated, it just will not focus. John