For giggles, I asked Grok about servicing this lens. Pretty general and not sure how accurate. ChatGPT’s answer was similar.
“Disassembling an LTM (Leica Thread Mount) Zunow 5cm f1.1 lens is a delicate process that requires precision, patience, and the right tools. This rare and vintage lens, originally designed in the 1950s, is a complex piece of optical engineering, and improper handling can damage its components or affect its performance. Below is a general guide based on common practices for disassembling LTM lenses of that era, as specific documentation for the Zunow 5cm f1.1 is scarce due to its rarity and the limited production by Zunow Optics. Proceed with caution, and if you’re inexperienced, consider consulting a professional technician.
### Tools You’ll Need
- Precision screwdrivers (small Phillips and flathead)
- Lens spanner wrench (adjustable, with flat or pointed tips)
- Tweezers
- Clean microfiber cloth
- Lens cleaning solution (if cleaning glass)
- Grease for reassembly (helicoid-specific, light viscosity)
- A clean, well-lit workspace with a soft surface (e.g., a microfiber mat)
- Optional: rubber gloves to avoid fingerprints on glass
### General Steps for Disassembly
1. **Preparation**
- Work in a dust-free environment to prevent contamination of the lens elements.
- Take photos or notes at each step to aid in reassembly, as the Zunow 5cm f1.1 has a unique optical design (5 groups, 9 elements, Sonnar-type).
- Ensure the lens is set to infinity focus before starting, as this aligns the helicoids properly.
2. **Remove the Front Retaining Ring**
- Inspect the front of the lens for a decorative or retaining ring around the front element. This is typically threaded.
- Use a lens spanner wrench to carefully unscrew the ring counterclockwise. If it’s tight, a rubber grip or slight heat (e.g., from a hairdryer) may help loosen it without forcing it.
- Once removed, the front element or group may be accessible. Note its orientation (e.g., which side faces forward) as it lifts out.
3. **Access the Optical Block**
- With the front ring off, the front lens group might come out as a single unit. If not, additional screws or retaining rings may secure it—use a precision screwdriver or spanner as needed.
- The Zunow 5cm f1.1’s optical block may separate from the focusing helicoid at this stage. Avoid touching the glass with bare hands; use tweezers or gloves.
4. **Remove the Rear Retaining Ring**
- Flip the lens to the rear (mount side). Look for a slotted retaining ring around the rear element.
- Use the spanner wrench to unscrew it counterclockwise. This ring often holds the optical assembly in place and separates it from the helicoid.
- Be cautious—the rear element is fragile, and excessive force could chip it.
5. **Separate the Helicoid and Mount**
- Once the rear ring is off, the lens may split into two main parts: the optical block and the focusing helicoid/mount assembly.
- Look for small screws or a helicoid key (a pin or guide) on the mount side that regulates focus travel. Remove these screws with a precision screwdriver to release the key.
- Mark the helicoid’s position with a pencil or tape where it separates to ensure proper reassembly later.
6. **Disassemble the Helicoid (If Needed)**
- To access the focusing mechanism fully (e.g., for regreasing), remove the chrome focus ring. This may involve unscrewing additional small screws on the front or side.
- Another retaining ring might secure the helicoid—use the spanner to remove it.
- The Zunow 5cm f1.1 uses a single helicoid (not a double helicoid), which simplifies reassembly somewhat. Note where the threads separate as you turn it apart.
7. **Aperture Ring (Optional)**
- If you need to clean or adjust the aperture, locate the screws or retaining clips around the aperture ring (typically near the middle of the lens barrel).
- Carefully remove these to access the aperture blades. Avoid bending the blades, as they’re delicate.
### Reassembly Notes
- Reverse the steps carefully, ensuring all parts align as they were originally.
- Apply a thin layer of fresh helicoid grease to the threads for smooth focusing, but avoid over-greasing, as it can migrate to the glass.
- Recalibrate infinity focus by adjusting the helicoid key and front guide pins if necessary.
- Test the lens on a camera body to confirm focus accuracy and aperture function.
### Warnings and Tips
- **Fragility**: The Zunow 5cm f1.1 is a collector’s item with intricate glass elements. Even minor scratches or misalignment can ruin its value or performance.
- **Variation**: Early “Ping-Pong Ball” versions (Type 1) and later improved models (e.g., post-1955) may differ slightly in construction. Examine your specific lens for unique features.
- **Expertise**: If fogging or sticky focus is your goal, and you lack experience, professionals like Kanto Camera in Japan (known for servicing Zunow lenses) might be a safer bet.
- **Cleaning**: Use lens-specific solutions and tools for glass surfaces—never use household cleaners.
Since no widely available manual exists for this exact lens, this guide adapts techniques from similar LTM lenses (e.g., Canon 50mm f1.5 or Leica screw-mount lenses). If you encounter unexpected resistance or complexity, stop and seek expert advice to avoid irreversible damage. Good luck with your Zunow—it’s a remarkable piece of photographic history!”
