Disassembly instructions 200mm f4

[peter]

Is anyone able to help me with instructions for disassembling this lens. I have

one in very nice cosmetic condition but the iris is sticky. I have screwed of

the front element (comes off relatively easily) and I think the mid section is

supposed to screw off too. But try as I might I cannot get it off. Its either

stuck, plain very tight or some other step is needed first. Also I am not sure

what follows in terms of getting at the diaphragm assembly to clean it.