Faster Than a Speeding Bullet

If you are over the age of 50, the phrase “faster than a speeding bullet” conjures up images of Superman. If you are younger than 50, perhaps you have visions of Neo dodging bullets in the Matrix.

Regardless, imaging at speeds “faster than a speeding bullet” and beyond has been a challenge for engineers and scientists. But those who have taken on the challenge have found both physical insight and beauty in the process.

The flash images that Harold “Doc” Edgerton created of a bullet piercing an apple and, more recently, Ramesh Raskar’s videos of “bullets” of light being scattered by water in a plastic bottle are cases in point.

Unprocessed image of a rocket sled acquired by a streak camera and illuminated by an Xe electronic flash unit.

An article published in Optical Engineering in August, “Digital synchroballistic schlieren camera for high-speed photography of bullets and rocket sleds,” describes a method for imaging fast-moving objects using conventional color CCD technology.

Authors Benjamin Buckner and Drew L’Esperance, senior scientists at MetroLaser, summarize the various approaches to high-speed imaging with streak cameras, which were traditionally film based, and the need and challenges of a digital solution. The authors then describe an innovative solution to these challenges that fits within existing off-the-shelf technology.

Buckner and L’Esperance use a galvanometer-based mirror system to produce the streak image on a high-quality color CCD.

Background-subtracted streak image of a 12-gauge, 00 buckshot round fired at 354 m/s.

Although the system is limited to F/10 or slower, the extra light needed for good-quality imaging was available through conventional flash systems.

Scan control of the mirror is critical and accomplished by a modest single board computer. Example imagery of shotgun pellets and a rocket sled are shown.

This well-written article clearly explains the technique at a level that both experts and non-experts in high-speed imaging can understand.

–SPIE Fellow Eddie Jacobs of University of Memphis is a member of the Optical Engineering editorial board.

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