Glass Exploding

Just been asked to throw some figures together for a high speed shoot. Using the photosonics action master 500. My query is 500fps fast enough for a demonstration of the effectiveness of armoured glass against a bullet hit? The photosonics is the only camera I can lay my hands on, so other suggestions are out the window I suppose.

Nick Paton

Director of Photography

Nick Paton wrote :

>Just been asked to throw some figures together for a high speed shoot. My query is >500 fps fast enough for a demonstration of the effectiveness of armoured glass >against a bullet hit?

In my opinion you want to be using a speed of 5,000 frames per second, with one of the "drum" cameras that rotate an approximate 3' foot long piece of film wrapped around the inner circumference of the drum that is spun at a very high speed.

I wouldn't expect that you will see much information with a bullet hitting glass at 500 fps. You will have a frame where the glass is un-damaged, and the next frame will have the bullet crater.

I just did a close up shot of a golf ball being hit by a golf club at 2,500 frames per second and the ball is in frame for 10 frames after contact with the club! Than and the club head speed is couple orders of magnitude slower than a bullet's speed.

An interesting note about the golf ball shot: the compensation for the speed, shutter angle, and the rotating prism in the Photosonics 4C camera operating at 2,500 frames per second is 9 stops! We lit the holy s--t out of the ball and surrounding grass with an 18k HMI and two 6K par's. If we let the lights shine on the ball and grass for more than 15 seconds, it would set the grass on fire and start to melt the ball! After the shot the golfer would walk, no, run away with his white cotton pants legs smoking.

The 1,000 foot film load lasts 7 seconds. The golfer that was hitting the ball was using glacier glasses like you would wear ice climbing, just so he could see the ball, and I was using gas welding goggles just to see what the lighting balance looked like. It was so bright, everything looked white hot to my naked eye with out the goggles.

Oh yeah, with Vision 320T film, and an 85 filter for color correction, I was at a 2.8 on the lens!

Fun stuff. We did the shot 13 times for various angles and playing surfaces to cut into the upcoming film "The Legend of Bagger Vance" using 13,000 feet of film. The boys and girls down at Kodak LOVE this camera! The golfer never missed, in spite of the fact that we had lights and cards set inches from the path of his swing.

Bill Bennett Los Angeles

Another lighting option I have used with high speed shots is to use very large magnesium flash bulbs as illumination. Some burn for over 1/30 of a second and can sometimes be syncronised with the camera and the event you are recording. Very large electronic flash/strobe units are also sometimes an illumination option too if a single flash has a long enough duration. Running a video camera and recorder is great for setting up and gettting your timing right before you expose any film.

Cya Steve

>Another lighting option I have used with high speed shots is to use very large >magnesium flash bulbs as illumination. Some burn for over 1/30 of a second and >can sometimes be syncronised with the camera and the event you are recording.

I would agree with the general opinion that (as described) you need very, very high speeds. Do you want to see the bullet moving, or are you trying to photograph the glass shattering? If the latter, then lower speed might work. If the former, it sounds like you need to bring in a specialist company.

The flashlight comment take me back to the time when I was a scientific photographer working for National Physical Labs. We had a special rig for illuminating high speed shots. it consisted of a lightbox with multiple PF60's wired up to run from a uniselector (a mechanical rotary switich used in old telephone exchanges) The whole thing was run from dry cells, wired to produce about 100v. It would fire off about 30 bulbs over about one second god it was frighteneing! And it was all too easy to forget that although it ran from torch bulbs, 100v was 100v, as I learned ony too rapidly!

Brian

Nick Paton wrote:

>My query is 500fps fast enough for a demonstration of the effectiveness of armoured >glass against a bullet hit?

Nick I think this may have been covered on the Archive.

You might want to look up the work of Edgerton.

I once was enquiring as to a similar thought as I own a Camera capable of 11,000 FPS ( however 5,000 FPS is it's top regulated speed) and wanted to do a bullet shot.

Some thougths. Shoot outside. Sunlight does not flicker.

If there is no info on the Archive I believe the I was told that a bullet will move 2 inches between frames, I believe that frame rate was for 5,000 FPS, but I can't remember.

You may need to find an armourer who can load a lower powered charge to slow the muzzle velocity down.

I did do a shot of a Balloon sculpture being decimated by shotgun Blasts, for an artist. At 5,000 FPS it was amazing. In the TK we slowed it down 3/4. We were lucky to find the right pyro guy.

Steven Gladstone

Gladstone Films

Bill Bennett wrote:

>((snip)).....We lit the holy s--t out of the ball and surrounding grass with an 18k HMI >and two 6K par's. If we let the lights shine on the ball and grass for more than 15 >seconds, it would set the grass on fire and start to melt the ball!.......

Thanks for the advice, all. I shall pursue other avenues. What about if I used a sledge hammer to demonstrate the same effect. I would imagine this would have a much slower travel than a bullet. The purpose of the shot is to demonstrate the glass's indestructability, not a bullet necessarily.

What a great list this is, Ta Geoff.

Nick Paton

Director of Photography

Nick Paton wrote :

>My query is 500fps fast enough for a demonstration of the effectiveness of armoured >glass against a bullet hit?

I think it might be too slow. It certainly won't "stop" a bullet in flight. For that you need (help me out, Jeff Kreines?) a Schlieren (Wollensak?) camera at around 10.000 frames (???). Oh well, that was years ago. Maybe there is something better now. Sorry to butt in...

Robert Rouveroy csc

The Hague, Holland