Paul C. Buff, Inc. Technical Forum

I apologize for such a stupid question, but what is a "t.1" method and a "t.5" method?

t.1 and t.5 are flash durations. It's a way of expressing how long a particular flash emits light. t.5 is the time it takes for the flash to emit half its power. t.1 is the time it takes to emit 90% of the power.

These are relevant when considering a flash's ability to freeze motion. If these durations are relatively long, then moving objects may be blurred in the picture. (Very similar to a slow shutter speed when using a continuous light source.)

The lower the t.1 or t.5 is, the more able the flash is to freeze motion. t.1 is a more sensitive indicator and discriminates more finely among flashes. That is, two flashes could have the same t.5 and this might imply that their motion-stopping capabilities are the same. But if, in fact, one of them had a lower t.1 than the other, then that flash would actually perform better. This is because the light emitted between the 50% and the 90% mark is capable of impacting the exposure, but is not accounted for in the t.5 measurement.

There is a long article about all of this on this website. Go to the home page, choose the help section>studio flash explained>flash duration.

Thanks. You answered my question with your answer. Now all I need is to find out the flash duration of an Ultra 1200 at full power. Most appreciated.

Here's the t.1 and t.5 times for all permutations of WLX. Ultra1200 durations are approximately the same as WLX1600 in "full mode" . . . 1/1600 t.5 and 1/530 t.1 @ full 640WS . . . about twice as long when dialed down to 1/32 power.

http://www.paulcbuff.com/x1600.php

So "t.5" is at 1/32 power?

Twice as long as 1/1600 (full power t.5) = 1/800 (1/32power t.5)