Earth rotation limits in-body image stabilization to 6.3 stops (2020)

What “stops” mean and how CIPA ratings work

• “Stops” here are doublings/halvings of light at the sensor, via shutter time or aperture.
• “Stops of stabilization” are defined via a CIPA test: compare the slowest shutter giving an “acceptably sharp” image to the old 1/focal‑length rule.
• Several commenters note that real‑world performance beyond ~4 stops often falls short of CIPA numbers.
• Discussion emphasizes thinking in shutter speed (e.g., 1/25 vs 1/2000) rather than equating stops directly to aperture.

Why Earth’s rotation limits IBIS

• Modern IBIS uses gyroscopes that can sense Earth’s rotation.
• A gyro maintains orientation relative to inertial space, not Earth’s surface, so it “sees” Earth rotating under it (Foucault pendulum analogy).
• For terrestrial subjects, camera and subject rotate together with Earth; trying to cancel that rotation misaligns camera and subject.
• Earth’s revolution around the Sun and galactic motion also exist, but their angular rates are much smaller, so they’re not the practical limit here.

Proposed technical workarounds

• Ideas raised:
  • Use GPS + compass + accelerometers + gyros (9‑DoF fusion) to estimate pointing and latitude and subtract Earth’s rotation.
  • Infer Earth rotation from gyro data alone via gyro‑compassing, or by filtering specifically at the known rotation rate.
  • Calibrate by having the camera sit still briefly and integrating gyro output.
  • Software filtering: high‑pass vs low‑pass treatment of gyro signals to separate shake from Earth rotation.
• Others argue GPS is unnecessary or even useless for orientation; inertial sensors alone suffice.
• Several note cost/complexity: aircraft/submarine‑grade INS is expensive; consumer MEMS gyros are noisy and drift.

Astrophotography and mounts

• For stars, compensating Earth’s rotation is desirable; IBIS that “tracks the sky” is beneficial.
• Equatorial mounts and tracking tripods already solve this for long exposures, sometimes with secondary guide cameras.
• Some camera systems use sensor‑shift for star tracking when GPS is available.

Debate over limits and products

• Some suspect regulatory/export issues (e.g., ITAR, missile guidance concerns) as a practical cap on gyro quality in consumer cameras.
• Others counter that consumer IMUs have surpassed older aerospace mechanical systems and cost is the real driver.
• Commenters note manufacturers claiming 8+ stops (e.g., certain Nikon and OM System bodies), questioning how this reconciles with a ~6.3‑stop theoretical limit and suggesting test‑optimization “dieselgate”‑style scenarios or narrow conditions.