Freeing a stuck aperture iris

[Doug Kerr]

This technique is probably well known to many of you, but I have just refined my description of it and I thought it might be of interest to some.

Often with older barrel lenses, especially those that have not been used for some while, we find that although the aperture iris at first seems to work all right, once we close the iris fully it will not re-open. Torque on the ring just makes the iris disk try to distort into a wavy mound.

The difficulty is often just a little bit of rust on the tips of the iris blades. When the iris is fully closed. they "pile on" pretty tightly, and thus just a little rust will prevent easy motion. Of course the tips are narrow and thus not too stiff, so they can't struggle against the problem.

My approach is as follows. (Of course, any reader would utilize it at his own risk, and we cannot be responsible for any result not found satisfactory!)

Three items are needed:

A. Some light instrument oil. "Instrument" here is a double entendre; it can mean either oil such as is used to lubricate shutters and other delicate mechanisms, or the types that are used on trumpet valves and trombone slides.

B. A pick made from a dressmaker's pin - the long kind with a small plastic ball on the end. They are available at many supermarkets. dollar stores, and sewing departments. Bend about a 1/4" portion at the tip end to an angle of almost 90 degrees. Be certain that the part beyond the bend remains straight.

C. A small paint brush (about 3/16"-1/4" wide is good).

Now to get started. Before starting each step, be certain to give thought to how you will hold the mount and how you will steady your working hand. The work isn't extremely delicate, but a slip would be disastrous.

1. Remove both element cells.

2. Using the brush, paint a small layer of oil over a circular area surrounding the central opening in the iris (perhaps 3/8" in diameter, but depending on the size of the iris). Do this on both sides. Wait a couple of minutes for the oil to propagate between the iris blades by capillarity.

3. With your finger, carefully press on the center of the iris so it deforms just a little bit. Release and do the same from the other side. Do this several times, alternating between the two sides of the iris. This will cause a little relative movement of the tips of the blades, loosening the grip of the rust and allowing the oil to proceed to the battle zone.

4. Identify a certain "starting place" among the iris blades. Take the pick (item B) and slide its tip gently between two adjacent blades a little way out from the center of the disk. Be sure the tip remains parallel to the blade surface. Then slide the tip gently toward the center of the iris as far as it seems to go gladly. This will separate the blades and break any adhesion between the rusty surfaces, and will also allow the oil to proceed further to where it is needed. Do this all the way around. (Note that in some irises, alternate blades or of differing shape, so don't get confused.)

5. Do that same thing from the other side of the iris.

6. Now try to open the iris. You may need to put torque on the ring and release it several times before the blades start to move. It may move only a little, and you may need to "rock back and forth" to free it fully.

7. If you are not successful at this time, repeat steps 2-5.

8. If the iris opens, do not open it all the way.

9. Close the iris, but not quite all the way. Open it (partway) and close it (not all the way) several times.
10 Now close it all the way. Check that it can be opened again (even if not gladly). If not, repeat steps 2-5.

11. Mop up the excess oil with a tissue. (Be careful that it doesn't get caught on the blades, especially around the opening.) You will probably see the oil a bit orange or brown in color as a result of the entrained rust particles.

12. Apply a new coating of oil on each side.

13. Open the iris partway and close it all the way several times.

14. Mop up the excess oil. Add new oil and repeat step 13 and 14 until the oil removed is "clear".

15. Complete the mopup of the oil. Do not add further oil.

16. Replace the element cells.


Best regards,

Doug

[C. D. Keth]

I thought I would add that people should be sure that their shutter does not have paper blades before they try this.

[Doug Kerr]

Hi, Christopher,

I thought I would add that people should be sure that their shutter does not have paper blades before they try this.)

A very good point. I wasn't really aware of paper iris blades.

Thanks.

Best regards,

Doug

[C. D. Keth]

German compound shutters have paper shutter blades that are very similar to carbon paper. Other shutters might have paper blades but I do not know about them. Just thought I'd mention it.