Drag racing

These are funny cars drag racing at the Orange County International Raceway in Southern California. I took this picture in the 80's with my first medium format camera, the Mamiya RB 67. I was seated in the bleachers as far away from the track as possible, which was much too far for a flash to be effective. There were photographers who had gained access to a ground level vantage point right up against the railing, and they all had portable flash units mounted on their cameras. This shot is a one second exposure, from a tripod of course. The illumination on the cars comes from the flashes of the other photographers. I captured multiple images from multiple flashes during the long exposure. Determining the f/stop, though, was a bit tricky. The formula is: GN = f/stop x flash-subject distance. Most portable flash units at the time had guide numbers of about 120, and I estimated the distance from the photographers to the nearest cars to be 15 feet. Therefore, plugging in the values: 120 = 15X where X = the lens aperture. Dividing both sides by 15, X = 8. So, I set my 500mm Mamiya lens (equivalent to a 300mm in the full frame digital format) to f/8. Remember, with film you couldn't see the results until it was developed, so I had no idea if my calculations (especially the flash-to-subject distance) were correct until the next day. I captured this with Kodak Ektacrhome 64. The flashes you see in the opposite grandstand would have been totally in effective, but those people didn't know it.