An Intuitive Explanation Using the “Western Wheel”
1. The Basic Idea: Why an Object Appears Stationary
A stroboscope produces short flashes of light at regular intervals. When these flashes occur at the same position of a rotating object every time, the object appears stationary to the human eye.
Formally:
- Object rotational frequency = f
- Flash frequency = f → correct "freezing" of the motion
2. The Problem: There Are Several “Apparently Correct” Frequencies
This is where the phenomenon of harmonic multiples comes into play.
An object does not only appear stationary when the flash frequency exactly matches the actual rotational frequency. A stationary image can also occur at:
- Integer multiples → 2f, 3f, 4f
- Integer fractions → ½f, ⅓f
These additional “stable” conditions are known as harmonic multiples.
3. The Western Example: Stagecoach Wheels
Imagine a classic wagon wheel from an old Western movie:
- The wheel has, for example, 10 spokes
- It rotates at a constant speed
Case A: The Correct Frequency
The stroboscope flashes exactly once per revolution.
- The same spoke always appears in the same position.
- The wheel appears stationary.
Case B: Half the Frequency (½f)
The stroboscope flashes only every second revolution.
- A different spoke is illuminated alternately.
- Since all spokes look identical, the eye cannot detect the difference.
Result:
The wheel also appears stationary - but incorrectly.
Case C: Double the Frequency (2f)
The stroboscope flashes twice per revolution.
- Two different positions become visible.
- These positions are geometrically symmetrical.
Result:
A seemingly stable image is produced here as well.
4. Why Our Eyes Are Fooled
The key point is:
- The eye does not recognize individual spokes; it perceives only a repeating pattern.
- When several positions look visually identical, our brain interprets them as being “stable”.
5. Typical Consequences in Practice
Without an additional reference (for example, a reflective marker):
- Multiple “correct” settings may seem possible.
- Rotational speed can be misinterpreted.
The operator must guess or compare different settings.
6. This Is Exactly Where AutoSync Comes In
The AutoSync laser function solves precisely this problem:
- It uses a unique reference point (reflective marker).
- The same point is detected every time.
- The flash is triggered only at that point.
As a result:
- No ambiguity
- No harmonic multiples
- Only one correct frequency
For an even more detailed explanation, see here.