Flash Burst Speed
Before you scroll down and look at the setup on how I took this photo. Click on it and take a good look at full size (1.4mb). It actually turned out quite well. The whole photo idea came from a discussion with my Bee Friend who has been taking photos of his bee hives – bees at high speed. The discussion was about the actual speed of your flash vs the speed of your shutter and that developed into a discussion on “shutter dragging” – this is part I of my posts on shutter dragging – using your flash to freeze motion in dark settings, while still having some of your background exposed.
Just to set the record straight, this photo is NOT shutter dragging, this is just plain old high speed photography using a flash as the light source. So you ask why am I talking about shutter dragging and how can this be part I? Simple, the two are completely related and if you fundamentally see and understand the speed of the burst of light from your flash and then you understand what flash sync speed is, you’ll totally just slip right into to a full understanding of shutter dragging and you can exploit it for yourself at a later time.
When you look at these photos you might think I have state of the art high speed photo equipment. Well I have great equipment, but it’s not special high speed equipment. You could actually do this yourself with a point and shoot, albeit a little more difficult and maybe not quite as much light to work with.
- 1 Pyrex pan (color blue)
- 2 blueberries
- 1 pencil eraser
- 1 mostly motivated assistant who understands timing is everything
- a bit of tap water
- 1 Camera (Nikon D7000) w/ Nikon 24-70 f2.8 lens
- 3 flashes mounted on stands 2 Vivitar 285HV’s (see my article) and 1 Nikon SB600
- 3 Cowboy Studio Flash Triggers (see my article)
Before you get all crazy on me thinking you don’t have the equipment, the lens was shot at f13, so you can use just about any old lens. Same with the the body. I could have done this with my D40 and the kit lens. All the extra flashes are just helpful, but you can do it with your on-board flash and you wouldn’t even need the Flash Triggers or stands. Though you are going to want a tripod and manual focus.
To take these photos I stuck the camera into manual mode, cranked up the shutter speed to 1/250th of a second (max shutter sync speed), fixed ISO to 100 and turned all the flashes on to 1/4 power (more on that later). I dimmed the lights in the room and then started off with an aperture of around f8. Fired a test shot and looked at the histogram to see my exposure. I kept cranking the aperture up until I hit just right at f13. You could do this just by looking at a preview, but the histogram makes it easy to see.
Once my exposure was just right, I then held something up in the dead center of my pan where I wanted the center of my focus to be. I used auto-focus to get focused, then switch to manual so it would stay focused in that exact spot. I then timed with my assistant dropping things in the water while I fired at my fastest frame rate (usually a burst of three images). Since I was at 1/4 power on my flashes I got a burst of three 1/4 power flashes no problem in quick succession without the flash having to recharge – that was a bonus as the flashes were able to take three to four shots in a row and keep up. The Vivitar 285HV by the way is an $89 flash. A bunch of trial and error later and we had our shots. Sweet. I will admit a point and shoot might be hard simply because of shutter lag, but it can be done if you time things right. Timing is obviously everything here.
So how and why did this actually work? If I had thought ahead I would have taken the shots with a slower shutter speed of 1/30th of a second to prove the point. Even with 1/250th of a second you are not going to freeze water in mid air. The first thing to know is the shutter speed had little to do with these shots or the exposure. I could have shot it at 1/15th of second or 1/250th of a second – it really didn’t matter. What mattered was that I was getting 99% of my exposure from my flash. The flash was so bright compared to the light in the room that the only thing I was getting was the burst of the flash. Think of being in a totally blacked out room when a flash photo is taken – you see everything for a very short time.
How long is the flash duration? Well that depends on the flash, power level, etc. Good studio lighting for example can be extremely fast (and bright). My SB-600 according to Nikon has the following flash durations:
1/900 sec. at M 1/1 (full) output
1/1600 sec. at M 1/2 output
1/3400 sec. at M 1/4 output
1/6600 sec. at M 1/8 output
1/11100 sec. at M 1/16 output
1/20000 sec. at M 1/32 output
1/25000 sec. at M 1/64 output
I honestly don’t know the flash duration of the Vivitar 285HV’s. But once I saw the Nikon SB-600 specs, I knew that lower power would yield faster bursts of light. I set everything to 1/4 power and got about 1/3400th of a second burst of light. Thats right everything was exposed for only 1/3400 of a second even thought he shutter was set to 1/250th. Wow! If I needed faster I could have lowered the power even more, moved the flashes in closer and got extreme stopping power of 1/25,000th of a second – do that with your shutter.
So thats the first lesson. A burst of a flash is very short and very fast. Where does shutter dragging come in? Well thats in part II when I can get some demo shots, but for now flash duration is this articles critical concept that I demonstrate in the photos above. I froze water in mid air simply by using my flash for the exposure and not how long my shutter was open. I was able to pretend my shutter was faster then it really was by having a bright flash.
My next article I’ll cover flash sync speed since thats the second concept you need to understand with shutter dragging. Your flash sync speed is the fastest your shutter can go without being in the way of the burst of light from your flash.