Andy Gock

It’s been a while since I’ve written a technical article. But today I’m going to talk about flash durations. After a bit of wild searching on the internet, I couldn’t really find any good resources showing actual real-word measurements of flash durations of speedlights, especially t.1 measurements.

I decided to do my own tests…

Canon 580EX at full power

Lights Tested

I decided I would measure the flash durations of various lights. Thanks to Refined Reflections for lending some of his lights to test.

These include:

• Canon 580EX
• Nikon SB-24
• Nikon SB-26
• Nikon SB-28
• Nikon SB-80DX
• Yongnuo YN560
• Cactus KF36 (Vivtar 285HV)

These speedlights above are all IGBT triggered power control, this results in shorter durations for lower power discharges.

There are also some results from:

• Broncolor Flashman floor pack with Pulso 2 head (1800Ws symmetric)
• Broncolor Impact 41 mono light
• Godox 120 Ws
• Alien Bee B400 160 Ws
• Paul C Buff Einstein E640 (640 Ws), measured for constant color mode and action mode
• “Mystery” eBay light 400 Ws

Here are the results I measured, these are real word measurements I personally performed on these flashes. Later in the article, I’ll describe, how I actually did the measurements.

I’ve also added some results of a few mains powered strobes for reference as well.

The Results

Canon 580EX

Nikon SB-24

Nikon SB-26

Nikon SB-28

Nikon SB-80DX

Yongnuo YN560

Cactus KF36

* This is the same as Vivitar 285HV

Broncolor Flashman with Pulso 2 head (1600 Ws)

I double and tripled checked this, the duration is really shorter at higher power!

Broncolor Impact 41 Monolight

Godox (120 Ws)

Alien Bee B400 (160 Ws)

Paul C Buff Einstein E640 (640 Ws)

We measured this under 2 modes, Constant Color and Action mode.

Under constant color mode:

Under action mode:

“Mystery” eBay light (400 Ws)

How I measured it

I built up a basic little circuit using a BPV11 phototransistor as the sensor. The output was then read by an oscilloscope and the t.1 interval determined by setting two cursors to correlate to the respective t.1 amplitudes.

The resistor was chosen so that the transistor always operated within linear regions, and collector current was within maximum limits allowed. The device never reaches saturation. It measures light between 620 to 980 nm, peaking at 850nm and has a turn on and turn off response time between 5 to 6 microseconds each (plenty fast enough for our measurements, within 5% for the fastest measurements) (- fixed typo on units, thanks Randy)

The t.1 (sometimes called t0.1) is measured as below:

Sample Discharges

I didn’t bother to save the waveforms for each test, it just would have taken too long. But I did keep a couple for my personal reference. Here are some of them, just as an example to see the shape of light output of the 580EX at different power levels.

The vertical axis is linear to the irradiance at the sensor, so something that is twice as high means it was twice as bright (one stop). From one image to another in the plots below, they are not to scale.

Canon 580EX at full power

Canon 580EX at full power minus one third

Canon 580EX at 1/4 power

Canon 580EX at 1/64 power

Final Words

This article might be updated later as I get my hands on more gear to test and add to the result list.

Leave a comment if you have any questions, or perhaps you’ve picked up a mistake somewhere.