I recently purchased a Taylor Hobson and Cooke Series II lens 15 inch f/4.5. It has several aperture blades out of alignment. I have repaired this problem with other much smaller lenses. However, with this one I cannot figure out how to get at the blades after removing the rear lens element and the retaining band. Can anyone tell me how to proceed from this point to gain access to the blades for re-alighnment. I would appreciate any help.