Right David, the back part of the lens, ( the metal part ) is just screwed into the front part, so you may need something like a tube that's a really good fit over this to either lock it back in place, or undo it out completely to do what you have to do. The inner sleeves are plastic, and my lens sleeve has actually split along its length, so when the lens is tightened its actually opening up the tube, so not retaining the tightness. This was probably glued in place originally and the heat over time has un glued it, however you could possibly re glue if you wanted. Front lens and second from front could be almost impossible to remove for cleaning, centre sleeve is slotted in 3 places for the focus fingers to engage with the outer sleeve, presumably where the the grease goes, mine needs redoing though, so a job to do now. If you have one of these and it has fungus you might not be able to remove it easily, the japanese lens tend to be better made, like 35 mm in construction, well at least the ones i've taken apart do, the sankyo f1.0 lens is a prime example, all metal construction, alloy front locking collar, done to a cost point. Anyway you have some info now.....