>Ok, so this is a CRITICAL piece of info. The question here is >whether you needed that 1/640 to freeze the rider or freeze >YOU. Assuming your comment about the barrel being the point >of focus and being tack sharp is correct, then you needed >1/640 to freeze the rider and not you. What is critical here >is that you need EXACTLY that same speed under strobes...with >your camera. > > >More lights shot at lower power greatly help your cause. >Fewer lights at max power works against you. What I am not >understanding here is why you are using flash at all during >the day. If you are using the flash just to get a little fill >light, you can essentially ignore the sync rating and shoot at >1/640. The ambient light is overpowering the strobes, the >shutter is freezing the action, and you should be good. It is >when the strobe begins to overpower ambient that you need to >worry about sync speeds.
I had a chance to play at home with the D600 and some Alien Bees AB1600s I used last weekend, as well as adding 4 AB800s to the kit. In the link that follows, I set up 2 AB1600s, then 2 AB800s and played with exposure, light power and f/stop.
Lights and camera set up 20'-ish from where I stood. To simulate motion. I waved my hands and moved around...yeah, I look like an idiot, but I don't have any horses or riders available at home.
You can see there's a difference between 1/200 and 1/250 (the latter which have banding at the bottom).
Camera originally set to expose for where I was. You can see that background really blown out. I was trying to shorten the AB1600s used in this series to see how it'd do. The last in the series, #0779, had them turned almost all the way down...the lights were exposed for f/10 @ ISO 400. The two right before them were around f/8 or so, which is why they're slightly darker. Even in these, there is motion blur in my hands.
The next series, with the blue sky, was shot with AB800s. I underexposed for the sky 2/3 of a stop, which is why it's blue, then kept turning up the lights until I got f/9 on the lightmeter. I then shot at f/13, which is why they're still dark. until the last couple, when I dialed the f/stop back to f9 to match the lights. Even at the beginning, with the AB800s turned all the way down, I still didn't get stop motion in the hands. The last image shows the setting on the AB800s for the final 4 images.
In order to truly be able to stop action....even with a camera that does 1/250...is going to be pretty tough to do. I just think that it's just enough with the 1Dx's synch speed to help, but when you really zoom in, there is still a hint blur, esp during the day.
Maybe some day I'll win the lottery then get some Einsteins with Pocket Wizard's High Speed Synch adapters and such so I can shoot at 1/640 and not worry about it.
I'm looking forward to this Friday, as I've another barrel race to shoot. I've the 3 AB1600s, and 4 AB800s available. Given the results from above, though, I have no idea what to predict. I'm hoping the extra distance will help with the fall-off/motion freeze.
The Nikon D600 has a 1/200th sync speed. Which for me means game over.
And as soon as I mentioned it on Twitter, I got a flurry of "Why does that matter?" tweets back. Here's why it matters.
When you are balancing flash in bright ambient, you start at your max sync for your shutter speed. That will give you the most flash-friendly corresponding aperture, whether you are normally exposing or underexposing the ambient.
Some cameras, including some Nikons (remember when you really cared, Nikon?) had standard syncs of 1/500th of a second. Which instantly made every flash you owned twice as effective.
Think about it: 1/250th at f/16 equals 1/500th at f/11. Since the flash only cares about the aperture, you could balance in the same light with half of the flash power.
Put differently: an Einstein 640ws monobloc, when used with a 1/500th syncing body, effectively becomes a 1280ws flash because that power is going up against an easier aperture in a daylight balancing situation.
Even better, due to the magic of some Nikons' electronic shutters, they could sync at any speed so long as the speed was longer than the flash's pulse length. Higher sync speeds equal much more flexibility with your flashes. Which means you can nuke the sun at distance with just a speedlight. Which is awesome.
The D600 takes a step backwards, with a max sync speed of 1/200th. This is the same math, but working in reverse.
True, it is only a third of a stop as compared to 1/250th. But with speedlights and daylight, that is a critical third of a stop. To be clear, this camera makes every single flash you own less effective.
Also, the difference between 1/250th and 1/200th sync is deadly when it comes to stopping action when balancing flash and ambient. 1/250th is dicey enough. 1/200th just doesn't work."