Strobe & Speedlight Output Waveforms

[mawyatt]

I've borrowed a LeCroy Oscilloscope and made some quick measurements of the Adorama Studio 300, XPLOR 600 (IGBT) strobes and the manual Zoom Flash Speedlight (IGBT).

These tests are not calibrated so just for reference comparison, and the waveforms seem slower (longer) than expected, this may be due to the photo detector setup which uses a LED in parallel with a 100K resistor as the detector. However this is still good for relative comparisons.

What's interesting is the Studio 300 doesn't vary in waveform timing much as you can see, however I've measured the output power with a Sekonic light meter and it's accurate over the whole range, including 1/10 Stop steps.

At 1/4 (75WS) the Studio 300 output has about the same time span as the Speedlight at full output (60WS) ~5.6ms, and at full output of 300WS is ~8.5ms. However the Speedlight is much quicker away from full output, with a time of ~1.1ms at 1/2 (30WS) while Studio Strobe is ~5ms (37.5WS).

The XPLOR 600 is faster (IGBT) at all measured power levels, with ~750us at 75WS (1/8 ) (Speedlight _5.6ms at 60WS (1/1)), and ~550us at 37.5WS (1/16) (Speedlight 1.1ms at 30WS (1/2)).

The XPLOR has a specified 1.35ms @ 300WS, 680us @ 150WS, 425us @ 75WS, 290us @ 37.5WS and 215us @ 18.75WS which seems to confirm that the measuring setup is showing slower results.

Anyway, here's a few of the waveforms collected.


















Best,

[Lou Jost]

That's very dramatic to see how fast the zoom flash quenches the burst, while the strobes drag on and on....that's really going to have an impact on their ability to freeze motion.

[rjlittlefield]

These tests are not calibrated so just for reference comparison, and the waveforms seem slower (longer) than expected, this may be due to the photo detector setup which uses a LED in parallel with a 100K resistor as the detector. However this is still good for relative comparisons.

I notice that all your graphs top out around the same height, and that the Studio 300 curves have a variable length flat-ish portion followed by what looks like an exponential decay. I'll bet that your photodetector is heavily saturating on most of the Studio 300's output, so what we're seeing as a long end is actually a lot lower amplitude than it looks in the graphs.

Clearly the photodetector is fast enough to catch interesting behavior, based on its rendition of the rise and fall of the Zoom Flash curves.

--Rik

[mawyatt]

That's very dramatic to see how fast the zoom flash quenches the burst, while the strobes drag on and on....that's really going to have an impact on their ability to freeze motion.

Lou,

I don't know if other speedlights behave like this, I don't recall the Younguno having such an abrupt waveform decay. Edit (just found some waveforms from a couple years ago and seems they also fall off quickly but it's hard to compare since the time scale is 2ms/div and a different setup was used). One thing to remember is to compare at the same output power not equal amount of back off.

Best,

[mawyatt]

These tests are not calibrated so just for reference comparison, and the waveforms seem slower (longer) than expected, this may be due to the photo detector setup which uses a LED in parallel with a 100K resistor as the detector. However this is still good for relative comparisons.

I notice that all your graphs top out around the same height, and that the Studio 300 curves have a variable length flat-ish portion followed by what looks like an exponential decay. I'll bet that your photodetector is heavily saturating on most of the Studio 300's output, so what we're seeing as a long end is actually a lot lower amplitude than it looks in the graphs.

Clearly the photodetector is fast enough to catch interesting behavior, based on its rendition of the rise and fall of the Zoom Flash curves.

--Rik

Rik,

It might be saturated, I just grabbed an LED and available resistor that was available. The relative waveform widths are what I think you can see from the waveforms. The Studio 300 shows the effects of voltage control for adjusting the power rather than gating the waveform as the IGBT enabled devices.

I might try and do some more tests with a different detector & setup if I get some time. From the above Younguno plots, the flat top of the Zoom Flash does hint at a possible detector saturation.

Best,

[rjlittlefield]

I might try and do some more tests with a different detector & setup

One quick and dirty approach is to just shield the detector however much is needed to keep it from saturating. Point it away from the flash, hide it in a mostly closed box, whatever.

--Rik

[mawyatt]

I just reran these tests with a different detector, used a 1N4148 silicon diode (found one) instead of the LED. Also used a small cup diffuser around the diode & resistor (100K). This produced better resultant waveforms IMO.

These are all still uncalibrated tests and only valuable as relative time base comparisons between different devices at same or similar power levels, so please note the actual power level (not backoff levels) and timebase, then compare waveforms.

For example: compare the speedlight at 60WS with two strobes at 75WS, or the speedlight at 15WS with the strobes at 18.75WS.

Best,

[Greenfields]

I attach a set of curves for the MT-24EX I made when the unit was new.










The noise on the traces is not "real" but a quantization artefact from the 8-bit analogue to digital converter of the digital storage oscilloscope.

The vertical scale should be mV not Volts.

Henry

[Lou Jost]

Beautiful fast-quenching curves! Though it looks like the lowest powers will not really put out their nominal amount of light. But I prefer that trade-off rather than the extended tails of the strobes.