Rusty iris blades - Asahi Takumar 135mm

Phil Rhodes · September 6, 2020

I just bought an extremely inexpensive Asahi Takumar 135mm f/3.5. It's an original Takumar, not the SMC or Super.

There's what looks like rust on the iris blades. I suppose it could plausibly be brown grease, but it looks powdery, as if it's being ground off as the iris blades move.

I'm tempted to dismantle the thing and at least apply some rust removal solution, which might leave bare metal patches on the iris blades but might prevent the elements from being contaminated by rust particles.

Any thoughts gratefully received. I only paid a tiny amount for it so it's not a big deal either way, but it seemed worth saving.

Dom Jaeger · September 6, 2020

Some iris blades deteriorate worse than others, usually what causes damage is either oil leaching from the grease onto the blades or coatings being scraped off over time. The danger with corrosion is that the blades fuse and the iris is destroyed when you try to open it. Excessive oil can do a similar thing by binding blades together, as well as adding unwanted reflection.

If you’re up for a challenge you can try to clean them, but be warned that iris reassembly can be a frustrating and fiddly task. Make sure to take photos before disassembly, and note if the blades are symmetrical or have a particular orientation. Usually they are all the same shape but not always.

To properly clean and treat iris blades you really need to remove and disassemble the whole iris assembly, and treat each blade. Trying to do this with an iris in situ is not advisable.

When I clean iris blades I either do it in an ultrasonic bath or with lens tissues. I use a cleaning agent similar to white spirit or lighter fluid, and I’m very careful not to bend or distort the blade. For corrosion you could also use a rust inhibitor, but avoid anything like WD-40 that has an oily lubricant added. If the coating has been damaged, I gently rub a dry, black moly paste onto the blades using cotton swabs - a very light smear, almost just staining them really. This helps both with friction and to reduce reflection.

Good luck!