Quote Originally Posted by Mark Elberson


f/5.6 is 5 stops slower than f/1(1.0, 1.4, 2.0, 2.8, 4.0, 5.6, etc) correct? Wouldn't you need an ISO of 3200 (100, 200, 400, 800, 1600, 3200) to maintain the guide number of 58m or 190'? I'm not being a wise-guy, I'm just trying to understand because I am not very well versed when it comes to flash-photography
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As the coffee kicks in, I realize you're quite correct. I shoulda known better than to type before coffee (and pop-tarts...).


So, ISO3200 at f/5.6 is going to be pushing the shutter speed limits of the camera, will be deep into high-speed sync territory, and will limit the contribution that your flash will offer. If used for fill, it might be enough. You may need to cheat in any way possible to get the flash closer to the subject. I used a remote flash to achieve this a week ago while shooting a bicycling event. On-camera flash contributed to the lighting of the scene, but all too often the remote flash was doing the heavy lifting. Here are a few examples:


All shots: 1D Mark III, 70-200/2.8IS, 580EX II on-camera, 580EX II off-camera on stand about 12' forward and to the left of the shots, shooting at about a 45' angle between down the road and across the road. Varying cloudiness all morning.


ISO 100, f/5, 1/200th, lens at 200mm (f/5 for more DoF, I think):





ISO 100, f/2.8, 1/640th, lens at 105mm (f/2.8 for thin DoF):





ISO 100, f/2.8, 1/320th, lens at 125mm:





You can see the ground "blast" of the remote flash, from left-side-near to right-side-farther-back.


As I understand it, using an on-camera flash to trigger remotes is power-hungry. I also knew that I'd be chasing some clouds all morning. In the hopes of simplifying the remote triggering, I spent most of the morning with the flashes set to manual 1/2 power and ignored how well they contributed to the shot. At times, I'd experiment with the flashes at full power. Towards the end of my time at this particular spot, the clouds really rolled in, and I was showing speeds of 1/200th at ISO 100 f/2.8. Full power flashes were too much, for almost any of the shots I was taking, so then I went E-TTL (auto flash exposure), possibly with some - flash exposure compensation dialed in (don't remember, and don't have the originals handy to check). I know it's not wildlife, but it's at least an example of some outdoor shooting. These were all done with a monopod, and the on-camera flash had a CP-E4 external battery pack (which I absolutely love, and think is an essential piece for any/every 580EX II out there!).


Over the course of about two hours shooting there, maybe 600 shots total and about 400 shots taken with flash, I absolutely drained the remote flash. It was dead as a doornail, not blinking its red ready light and it probably just went to sleep. The on-camera flash was getting tired too, and then I swapped the three sets of batteries (1 in flash, 2 in battery pack). These shots were challenging, as I had to balance the desire to capture expressions with waiting for the riders to ride into my "prime" flash coverage zone.


Thankfully, this guy just struck his pose and rode with it: