200mm f4 SMC (M42) - How to repair

I have a beautiful 200mm SMC with oily aperture blades that I'd like to fix. I am experienced, just not with Takumar telephotos. Does anyone know the easiest way to get to the aperture blade assembly?

An exploded view would be helpful as well.

Thank you.

As a general rule, the aperture blades are closer to the rear of a lens than they are to the front. So I usually "attack" from the rear. You'll need the correct tools for this process, chief among them in this case being a good lens spanner. The rear element or element group should have a slotted retainer ring holding it in place. Use the spanner to loosen and remove this ring. From that point, it's just a matter of removing the next element or group until you get to the iris. What I will often do is clean the iris in situ. I use a good solvent to remove the oil from the blades. Alcohol is often a good way to go. I carefully apply it with clean cotton swabs. Often it takes several applications of the solvent before all the oil has been removed. If you use alcohol, keep in mind that the alcohol you buy from the drug store often has a significant amount of water in the mix. The label will usually state what the alcohol percentage is. Obviously, the less water the better. When you apply this solvent to the blades, you'll see how the alcohol evaporates faster than the water, often leaving behind some amount of water on the blades. You want to be sure to remove this water with one of your swabs. The iris should be bone dry when you're done. When cleaning an iris this way, usually the element in front of the iris gets smudged, so it will need to be carefully and completely cleaned with lens cleaning fluid before reassembling the elements or groups.

Obviously, this is just one way to do things. If you want to strip down the lens completely, that will involve a much bigger process, where you'll have to deal with disconnecting the focusing helical as well as removing the collar and sleeves as required. Usually this will also involve removing tiny grub screws, which can often be easily damaged -- or lost if you're not careful. Just pay attention to the way things come apart, and if you're disconnecting the helical, it helps to mark the parts so that you know at which position they go back together so that infinity is preserved.

Good luck!