Just a little reminder for those of you that may have forgotten. One of the most basic and important things I’ve learned about photography is that when you’re using flash, ambient light is controlled by adjusting shutter speed. Flash exposure is controlled by adjusting aperture. Tweaking ISO lets you adjust the range of the Shutter and Aperture. In other words, if you could have any shutter speed and any aperture and control or provide any amount of flash you could control how any exposure is made. Whoa, that’s a lot of “any” for one sentence.
Most cameras have limitations. One limitation is the “Sync Speed”. It took me a while to grasp the idea of Sync Speed. Its actually more simple than I first thought. In short, Sync Speed is the fastest shutter speed your camera can use and still be able to synchronize with your flash – that your flash is lit at the right time to fully expose your image as the shutter opening passes over your camera’s sensor or film.
Most current cameras are around 1/200 – 1/250 of a second. In years past the sync speed/shutter speed limit was about 1/60th. My old film body was 1/60 when ever you put on a flash. My Nikon D300 is 1/250. If you shoot faster than that you start to get part of the sensor covered by the shutter during the exposure and you get at least a black band across the bottom of the image and that looks like crap.
This photo was taken during the day in my neighbors back yard at 1/1600th of a second using two Nikon SB flashes.
I can hear you saying, “But, you said your flash sync limit is 1/250th. And what are you talking about, “during the day and outside? It looks like you put up a black backdrop.”
Enter High Speed Sync (HSS). HSS is a way to make your flash go faster. On Nikon HSS is also called Focal Plane (FP) shutter sync. HSS works by firing lots of little flash bursts the entire time the shutter is open. This makes sure that the flash output is “available” during the entire pass of the shutter curtain as it goes by the sensor. (I should mention that the shutter curtain works differently at higher speeds in the way that the curtain opens. Here is a great and detail explanation). The downside of all this magic is that the series of flash bursts are not as powerful as one big release of the flash energy so you’ll need to keep that in mind as you determine exposure.
So what does HSS get you?
Since I was able to shoot this at 1/1600 I was able to kill ALL of the ambient light in the photo. There are trees and grass and my shed behind the bird. You just can’t see them because they shutter was fast enough to eliminate the light on the sensor. The two SB flashes were able to fully light the bird and feeder.
I used my RadioPopper PX system to trigger all of this which is pretty cool. Most trigger systems don’t exceed the cameras mechanical shutter sync speed unless you have an electronic shutter working for you but the Radiopopper PX works the Nikons CLS and does it nicely.