Submitter's name:	Mark Marr-Lyon
Title:	Green Flash
Gear used:	OM-4T, Zuiko 21mm f/3.5, and a tripod.
Diaphragm:	f/16
Shutter speed:	About 1 minute (auto +2 stops overexposure).
Film used:	Kirkland (Agfa) 200
Subject information:	The lab where I work. Two pulsed Nd:YAG lasers (the green light) are used in our experiment to freeze the high-speed (about 100 meters per second) motion of gas accelerated by a shock wave. The red light is from the safety interlock warning signs, since these lasers are powerful enough to cause significant eye damage. I have always liked the green color of the lasers, but due to the intensity of the light couldn't look at the beams, so I took a picture of them.
Technical information:	I didn't use a normal flash, but since the lasers have a pulse duration of less than 100 nanoseconds (1/10,000,000 second), I thought they would count. Normally the beams aren't seen as well as they are in the photo, but some theatrical fog was spread around the room to make them more visible. The lasers were set to pulse about twice per second, and I set the camera on auto and at f/16 for the greatest depth of field. The picture overexposed by 2 stops looked the best.
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Comment left by: Olaf Greve (no e-mail specified)

Brilliant shot, and a very original interpretation of the "flash" concept as well ;) As discussed off-list between me and the photographer, I too had been playing with this idea (for TOPE 2), but in the end I never carried it out. This picture has inspired me to do try to take such a picture someday, though.

Comment left by: Mickey Trageser (no e-mail specified)

I thought I had tuned into a sci-fi thriller! Nicely done.

Comment left by: John A. Lind (no e-mail specified)

I was wondering if someone would push the envelope on the definition of a "flash" and glad someone did, especially in a fashion which required some imagination and ingenuity to make an original image. Nice composition and use of the 21mm lens to "take it all in" too.

Comment left by: Henrik Dahl (hdahl@privat.utfors.se)

One word: cool!!!

Comment left by: Ralf Loi (no e-mail specified)

Think about moving your "flash" around... not very portable! I like the composition and the bi-color effect.

Comment left by: The Photographer (no e-mail specified)

Haha! You've got me there! The laser producing the beam in the foreground is reasonably luggable, meaning that it only uses normal household AC voltage and doesn't need to have an external cooling system. One person could probably even carry it. The laser producing the brighter beam in the background, on the other hand, occupies most of a 4x8 foot optical bench, requires two cooling water loops, and needs about 1000 pounds of 220 VAC power supplies! In fact, it was easier to move the experiment to the laser than the other way round (you can barely see the hole cut in the wall for the beam to pass through). Thanks for the comments. I like how the red color turned out too.

Comment left by: Wiliam Wagenaar (wiliam@zeelandnet.nl)

I love this one, but I wonder: 2 stops OVER exposure? Looks more like two stops under. Was it due to the intensity of the laser that the meter was fooled or was it the reciprocity failure of the film?

Comment left by: The Photographer (no e-mail specified)

Yes, I'd guess that reciprocity failure would play a large role here. With pulse durations so short, I'd also guess that the camera meter couldn't quite keep up either, but would do better than the film. I'm just glad that the red and green lights are fairly well balanced in the photo, since to the eye the green laser light is much brighter. I would think that with another 2 stops overexposure, the highlights in the laser, as well as from the red light would be rather blown out, but the rest of the room might start to be visible from scattered laser light.

Comment left by: Jim Caldwell (jamesfc@gte.net)

Really cool picture - I expected to see the Terminator lurking around the background! I was also surprised that this was 2 stops over - I would have guessed underexposed as well!

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