August 6, 2010
I hope this doesn't sound like an advertisement, but I love my Pocket Wizard Mini TT1. There are several things I like about it, but the most important to me is the ability to cheat the synch speed on my camera so that I can overpower bright sunlight with a small flash.
First, a little background. Modern DSLR cameras use a focal plane shutter mechanism. You can read more about the details, but the basic process is that there are two curtains. When you take a picture, the first one opens the window followed by the second one to close the window. For long exposures, say 1/2 second, there will be a pause of about 1/2 second between the first opening and the second closing. For really fast shutter speeds, the whole window is never open all at once. In fact, the second curtain will start closing before the first is fully open. In effect, there is a slit of light moving across the sensor. For most cameras, the fastest shutter speed when the whole sensor is exposed at once is around 1/200th to 1/250th of a second. That's the advantage of a focal plane shutter, the moving slit can be made very narrow so that it can achieve very high shutter speeds.
The drawback to a focal plane shutter comes when you want to use a strobe. Since the flash from a strobe is very short, like 1/2000 of a second, the strobe will only illuminate the portion of the sensor that's being exposed at that time. So, the fastest shutter speed you can use with a strobe is determined by the fastest shutter speed when the entire sensor is exposed. That's called the camera's synch speed. If you take a picture with a shutter speed faster than the synch speed, a portion of the image won't be exposed by the flash. Normally, the bottom half of the image will be too dark since it wasn't exposed to the flash.
Now, the folks at Pocket Wizard have found an ingenious solution. The Mini TT1 allows you to change the timing of when the flash fires. It turns out that there is quite a bit of wiggle room above the camera's native synch speed. There are a lot of variables, depending on your camera and flash, but I've been able to get usable synch speeds as high as 1/1000th of a second, which is a full 2 stop gain. All of a sudden, my little battery powered flash gains a 2 stop advantage against the sun.
Take a look at the examples below, and note the shutter speed shown above each frame. I'm getting nearly full-frame illumination at 1/500th of a second, and still have most of the frame at 1/1000th. The beauty is that when you're
In an indoors setting, I certainly couldn't use the high shutter speeds, but you don't normally need them indoors. The advantage comes when you're working outside in bright sunlight. A normal sunny exposure at ISO 200 would be 1/200th at f/16. Since the flash duration is so short, the shutter speed doesn't matter to the flash exposure, it's only controlled by the f-stop. At f/16, you'd need a really powerful strobe. But, if you can increase the shutter speed, that allows you to open up the f-stop so the strobe contributes more to the exposure. Normally, the goal is for the strobe to be somewhere between just under the ambient sunlight to a little brighter.
The photo below is a test shot of me in front of our house. For the first photo, there isn't any strobe, so the shadows are pretty dark. In fact, my face would have been a lot darker if it hadn't been for the porch and house reflecting some light back. The photo was taken at ISO 200, 1/350th of a second at f/8.
For the next image, I added a strobe to help fill in the shadows. The exposure is the same 1/350th at f/8, but this time there is a Canon 550EX strobe at 1/4 power shooting through an umbrella. The surface of the umbrella is about six feet from me. The result is a nice balance between me and the background. Even loosing one or two stops through the umbrella, I can use my strobe at 1/4 power so I get quick recycle times and long battery life.
Of course, I can push it further. The three images below were done using the same setup, but at 1/500th, 1/750th and 1/1000th of a second. As expected, the flash doesn't illuminate me at the bottom of the frame, but in this setting, it doesn't really matter. You might even say it's a little bit of an advantage since it helps to focus the viewers attention on my face instead of my stomach. None of the photos are cropped. I had zoomed in with the lens for the last frame.
Keep in mind that I'm shooting these as horizontals, through an umbrella, and at 1/4 power. If I wanted to shoot a full-length vertical, such as an outdoor bridal portrait, I'd have the entire top to bottom of the frame illuminated by the strobe - just keep the bride in the center. If I wanted overpower the sun even more, I could turn the strobe up to 1/2 or even full power and gain two more stops of light. If that wasn't enough, I could loose the umbrella and use a bare flash and gain another one or two stops.
The control that makes all of this possible is the hypersynch offset. You set it by connecting the Mini TT1 to your computer through a USB connection. Finding the right setting can involve some trial and error. So far, I haven't found the suggested starting points on the PW web site to be very useful. Too little offset, and you still loose the bottom of the frame. Too much offset, and you loose the top of the frame. I try to find a setting that takes some off the top, but more off the bottom, since the bottom portion of the frame is usually less important. If I do find a situation where I need more flash exposure on the bottom, I can shoot with the camera upside down.
Our modern tools really blow me away! When I started out in photography, most cameras would only synch at 1/60th of a second, so there was no practical way to use a strobe outdoors. When we wanted fill flash, we had to use flash bulbs since they have a relatively long burn time.