Yongnuo RF603 wireless flash trigger delay
Yongnuo RF603 wireless flash triggers
During the photo shoot with my daughter in the studio I realized something odd. The D800 is supposed to have a minimum flash synchronization time of 1/250s. This is the fastest shutter speed at which the camera can still communicate in time, so that the flashes triggers when the sensor is fully exposed and not partially covered by one of the shutter blades (fast shutter speeds mean, that the second shutter blade is closing while the first shutter blade is still in motion, so that the sensor is never fully exposed. See this highspeed-video from 0 min 36 sec).
With the flash sync time of 1/250 I set my camera to 1/250s and started shooting. And bummer, the bottom part of the image was black. Long story short – I investigated this issue a little further and made test shots, triggering the flashes both with the Yongnuo wireless units and the sync cable which came with my studio flashes. I have used different channels on the RF603 units to rule out interferences with other equipment and also used them on my Nikon Speedlights.
Results see below. Sorry for the tasteless composition, I took what I could find in five seconds 
Studio flash, triggered with the Yongnuo RF 603 wireless unit – ISO 100, 1/250, f4
In this image the flash was triggered using the wireless units. As you can see, the bottom part of the image is black. This means, as described above, that the flashes got the signal to fire too late, the second shutter blade was already closing before the sensor. The Yongnuo RF603 needs the fraction of a second to process and relay the signal, inducing a delayed flash trigger. The result is this black strip.
Cross-check: same camera settings, same setup, flash triggered with a sync cable. Result:
Studio flash, triggered with a sync cable – ISO100, 1/250, f4
No black strip. The image is a little darker in the lower half, but that is due to the alignment of the softbox and has nothing to do with the timing of the flash.
Conclusion: I guess this is the price for a low price – I got the four Yongnuo units for around 55 Euros, which is an excellent deal. The units have a very good build quality, They do not feel “plasticky cheap”, they sit firmly on the hotshoe and the connectors make a solid impression. In the battery compartment are four DIP-switches to select channels – meaning they have 16 different channels on which they can send so that your units won’t interfere with Yongnuo units of other photographers which happen to be nearby.
Anyhow, due to the delayed trigger signal you lose the option to shoot at 1/250 sec when using the RF603. 1/200 sec is the fastest shutter speed you will be able to use. If you can live with that, it’s fine. I suppose that high-end radio triggers like the PocketWizward do not have such a delay, but a PocketWizard also comes with a hefty price tag.
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They all do that, guv.
Radio triggers all introduce some delay, some more than others – even the expensive ones tend to delay by around 600 microseconds (e.g. PocketWizard). I have some Yongnuo RF603s and measured them at 1.25 ms (1250 microseconds) with an oscilloscope. In other respects, though, they are super – reliable, long range, etc. The delay is taken care of by dropping the shutter speed. 1/200s is 1ms longer than 1/250 sec, and with my D700 (which will actually sync at 1/320 using a cable) I find 1/200s is OK with these triggers. Optical slaves are much quicker (about 60 microseconds), but less versatile.
Studio photographers routinely drop to 1/200 or 1/160 when using radio triggers, it’s the price you pay for cordless convenience, no biggie if the ambient light is low and/or goes away during the exposure (modelling lights).
Hi Carl,
thank you very much for this very conclusive background information, appreciated !
Julian
Interesting article – I just ran into a similar problem trying to sync two YN-560ii flash units using the RF603 wireless units. Specifically, I was trying to catch a fast moving subject at night via a short duration flash (and low shutter speed). One flash was attached to the hot shoe on my camera via an intervening RF603 unit, the other was attached to a RF603 unit on a free standing tripod. Unfortunately, the resulting images had a slight double exposure, presumably caused by a slight delay between the on camera flash (which I assume is short circuited through the RF unit to the camera) and the free standing flash (which was triggered via the radio signal).