The Science of Poi Filming: How to Capture Fire Trails in Motion
Author: Yuta
Date: September 8, 2012
Introduction
This article explores the relationship between camera settings and the visual outcome of poi (fire) performances. Based on personal experiments and observations from 2012, I examined how resolution, frame rate, and shutter speed affect how fire trails appear on video.
Resolution & Frame Rate
- Full HD (1920x1080) is ideal in terms of image quality, but most DSLRs max out at 30fps.
- For fast poi movements, HD 720p at 60fps provides smoother motion and clarity.
- Panasonic compact cameras began offering 720p at 120fps, indicating the future of high-FPS video.
Key Questions
- How is 60fps footage handled when played back at 30fps?
- Should editing sequences match recording or output frame rate?
- How does slow-motion software like Premiere handle frame interpolation?
Shutter Speed & Frame Rate
Using 60fps with a 1/60 shutter speed exposes each frame fully. Some cameras support longer exposure—how they handle data across frames is unclear (see reference).
Fire Movement & Exposure
- Slow Poi: Overexposed due to lingering brightness.
- Fast Poi: Less overexposure, more clarity.
- Very Fast Poi: Trails break up, creating jittery visuals.
Trail Gap Formula
To estimate trail gaps:
G = Poi speed × { Gap Speed + (Frame Speed - Shutter Speed) }
The smallest gap occurs when shutter speed equals frame duration.
Conclusions
- Match shutter speed to frame rate for smooth trails.
- Use ND filters to control exposure without changing shutter speed.
- Long exposures can extend trails artistically if well-exposed.
Final Questions
Is fire brightness constant regardless of movement? How does wind affect fire visibility? This may warrant further study—maybe a university thesis?
Suggested Settings
For 720p/60fps:
Use 1/60 shutter speed, adjust with aperture/ISO, and add ND filters if needed.
For very fast poi:
Even with post effects like echo, gaps may appear—setting optimization is key.
