Overview

Repair of a Petri lens with a stuck aperture (Petri C.C Auto 55mm F2).
The cause was aperture blades sticking due to viscous oil residue.
The aperture was cleaned and the helicoid was re-greased.

Note: This article is based on repair work done several years ago and was written using videos and memory, so some details may be vague. Thank you for your understanding.

Symptoms

The symptoms were as follows:

• The aperture does not move at all
• The helicoid feels heavy (but is not seized)

Suspected Cause

The aged grease appears to have separated, allowing oil to seep into the aperture blades.

Disassembly – Pay Attention to Petri-Specific Construction

⚠️ Prerequisite: Intended for those with experience in disassembling, cleaning, and re-greasing old lenses

1. How to Remove the Special Lock Pin (Petri Lenses)

Petri lenses use a unique type of lock pin.

Some people modify pliers or screwdrivers to make a dedicated tool, but I simply filed down a pair of tweezers to create a basic tool.

Tweezers Selection and Customization

For this task, I selected a pair of tweezers from my stock with curved, relatively thick tips.

Cheap tweezers made of softer alloys with rounded tips are actually ideal because they are much easier to modify.

If you’re looking for suitable candidates at a 1 dollar store or a local discount store, I recommend checking the false eyelash or nail art sections in the cosmetics department first.

The hygiene/first-aid aisle is your next best bet.

Search results for “Tweezers Eyelash Rounded”(Amazon OneLink affiliate)

2. Beware of Ball Bearings Falling Out (Around the Aperture Ring)

Several ball bearings are used around the aperture ring, so be careful not to lose them.
Working inside a plastic bag is effective.

Aperture Cleaning and Helicoid Re-greasing

1. Cleaning the Helicoid

After roughly removing dirt and old grease, the helicoid was soaked in benzine(lighter fluid / naphtha).

2. Disassembly and Cleaning of Aperture Blades

Because oil contamination was severe, the aperture was disassembled and cleaned with benzine(lighter fluid / naphtha).

3. Notes on Lens Cleaning (Using Alcohol)

The lens elements were wiped using rubbing alcohol and lens tissue.

Alcohol can negatively affect lenses and other parts in many cases.
In general, washing with warm water and neutral detergent is recommended.

4. Reassembly and Grease Application Guidelines

Reassemble the lens in the reverse order of disassembly.
Be careful not to lose the ball bearings.
Apply a very small amount of optical grease (about the size of a grain of rice) to the helicoid using a brush.

Operational Check

Both the aperture and helicoid operate smoothly.

Lesson Learned / A Common Pitfall

I forgot to reinstall the automatic aperture linkage pin and had to disassemble and reassemble the lens again.

Conclusion

The failure was caused by oil separating from old grease and seeping into the aperture blades, resulting in poor operation.
Aperture problems caused by degraded grease like this are often relatively easy to fix if the lens can be disassembled.

YouTube Video

In the video, heavily soiled brass parts are cleaned using citric acid.
They come out shiny and satisfying to look at, but though it’s mostly for aesthetics.