Mechanical shutter blades of high-speed continuous shooting cameras: mechanics of carbon fiber materials and fatigue testing for hundreds of thousands of shutter lifespans

1. The microscopic violent mechanical environment in which the shutter blades operate

The focal plane mechanical shutter curtain is no ordinary small piece of iron. It is the core of precision machinery with the highest motion acceleration and the most terrifying mechanical load in the entire camera:

• Extreme life and death rush in milliseconds:
• The shutter curtain must span the full 24 mm vertical height of the full-frame sensor within 2.5 ms to 3.0 ms;
• Curtain starting acceleration exceeds 1000 G (equivalent to more than 100 times the overload limit of a fighter pilot!);
• The devastating impact of the final brake:
• When racing to the finish line at tens of kilometers per hour, the blades must be violently stopped by the mechanical brake damper within a stroke of less than 0.1 mm;
• Huge alternating bending stress (Bending Stress) will instantly conduct repeated oscillations along the blade sheet.
• Fatigue Achilles’ heel of traditional metal materials:
• When ordinary duralumin alloys or titanium alloys are only 0.05 mm thick, the microscopic metal lattice will inevitably produce microscopic slip cracks (Fatigue Microcracks) after experiencing 100,000 to 150,000 times of high-speed and severe bending impact. Eventually, it will completely break and shatter during a certain firing, and the shutter blade will get stuck on the light path like a rotten vegetable leaf.

2. Physical subversion of carbon fiber reinforced resin composites (CFRP)

The top industrial shutter blades fully incorporate Carbon Fiber Reinforced Polymer (CFRP) and aramid fiber (Kevlar) originally used in spacecraft and F1 racing cars:

• Dimensionality reduction of specific strength and specific modulus:
• The density of carbon fiber blades is only 1/4 of steel, but the tensile and bending strength is more than 5 times that of high-strength steel;
• Ultra-Low Moment of Inertia:
• The weight of the blades is reduced by more than 40%, which greatly reduces the kinetic energy consumption of the electromagnetic micro motor when driving the curtain to start and brake;
• Enables the mechanical shutter continuous shooting speed to be forcibly increased from the traditional 8fps to 14fps ~ 16fps pure mechanical speed;
• Infinite fatigue life limit (Fatigue Endurance Limit):
• The carbon fiber polymer chain has extremely strong self-absorbing damping and shock-absorbing properties under alternating stress, and will not produce dislocation fatigue cracks like metal at a microscopic level, giving the shutter a rigorous industrial-level continuous firing guarantee of 400,000 to 500,000 times;
• Self-lubricating and anti-thermal expansion coating:
• The blade surface is covered with an extremely thin dry lubricating film of nanoscale molybdenum disulfide ((\text{MoS}_2)) or polytetrafluoroethylene (PTFE / Teflon). The dimensional deformation is less than 0.001 mm in severe cold (-20°C) and scorching heat (+50°C), eliminating friction and jamming.

3. The ultimate fate of mechanical shutter in the mirrorless era: Farewell from carbon fiber to global shutter

With the faster-than-light iteration of semiconductor technology, the mechanical shutter itself is ushering in a historic curtain call:

• Historic decision of Nikon Z8/Z9: completely eliminate the physical mechanical shutter!
• Relying on the ultra-high-speed full-pixel circuit scanning speed of 1/270 seconds of the underlying stacked sensor, which directly eliminates all mechanical curtains and carbon fiber blades;
• The concept of shutter life is completely zeroed: As long as the sensor chip is not burned out, the electronic shutter can theoretically be fired hundreds of millions of times with zero wear;
• Sony A9 III Global Shutter:
• All pixels are sensitive to light and freeze charges at the same microsecond instant, completely ending rolling shutter streaks;
• Retain daily maintenance for mechanical shutter models:
• On models that are still equipped with a mechanical shutter, if the "Shutdown shutter curtain protection and dustproof function" is turned on when switching off the camera and changing the lens;
• Remember it is absolutely forbidden to touch the dust-proof shutter blade with your fingers! The fragile micron-level blades will undergo permanent deformation and derailment as long as they are subjected to a small vertical pressure from the fingertips. Repair and replacement require an overhaul of the entire machine.

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