Flash Duration for Studio Flash – Monolights
Flash duration is measured in two different ways. These methods of describing flash duration define the time as the flash begins to glow and then dims at the end of the flash. The methods are referred to as t.5 and t.1. As you can see the t.5 describes the duration above 50% of the maximum brightness, and the t1 describes the duration of above 10%.
The t.5 duration is generally the method used by manufactures in specifications of their lights. This t.5 reference is not the best indicator of stop action capabilities of a flash. The t1 method gives us a better indication action stopping of a flash. T.1 durations are generally 3x the duration of a t.5. For example a monolight flash that is rated at 1/900 t.5 will have the action stopping of a 1/300, not really much action stopping.
Here is something that many photographers are not aware of, most every manufacturer of monolight flash units vary the power delivered by “varying the voltage to which the flash capacitors are charged.”
This has the result of making the flash duration about twice as long at 1/32 power than it is at full power. In our example above of a monolight with a t.5 of 1/900 is in effect a 1/150 at 1/32 power.
Flash duration of 1/150 is not much action stopping, problems may become apparent when shooting a fast moving shoot handheld with a 200mm lens.
- T.5 designation is a bit misleading
- Monolight systems generally produce longer durations as the power is reduced.
Monolight are the favorite of lots of run and gun shooters, like wedding and location portrait shooters. We love the fast pack up and go that a monolight offers and also the ability to finely adjust the power to each unit. This flash duration issue does however cause us to think twice about selecting monolights for our work. Lets take a look at a popular and well respected system the Calumet Travelite 750.
Calumet Travelite 750
This is a powerful flash that has a t.5 flash duration at full power of 1/600. That means that it has a t.1 full power duration of around 1/200s. Now if we use the flash at 1/32 power the flash duration is about 1/100. If you are shooting this flash at a shutter speed of 1/200 you are clipping the duration of the flash. My guess is that the common user is not aware of the facts about this flash.
In a given product line say alien bees you will see that the lower power units always offer the the fastest flash duration. I have included a screen grab and a link to the Alien Bee Site. There is a ton of great reading and learning there.
The latest cameras have incredible high ISO performance, so why do we need so much power? The low power choice of a monolite gives us CHEAP and FAST DURATION.
I am really impressed with the Alien Bees, they just look a little dumpy. I guess you just have to keep a sense of humor about yourself.
I am thinking about a B400 and a Vagabond II kit. Ok, the 400 is $224.95 and the Vagabond II is $299.95, that means for $525 you can have can have lot of fast duration flashes with out plugging in. Now, just what color??
Here is a look at the Vagabond II, It looks like a together product and cheap. The B400/Vagabond combo would produce 2400 full power flashes with a .7 sec recycle!!
Photographic Education - JerryCentral 