Today I took out my two Nikon bodies and decided to test them with my cheap-o Gadget Infinity (aka Poverty Wizard) radio triggers and my Nikon SB600 flash. I put my artificial light up against the Arizona sun in what we photographers love to call Overpowering the sun with flash.
Something unknown to most novice photographers is a camera's flash sync speed. Most camera's these days can achieve a very fast shutter speed ranging from 1/4000th to 1/8000th of a second. YES, VERY FAST!! However, to achieve such fast speeds, the cameras play a little trick where the shutter doesn't open completely during the fast shutter speeds, but rather travels along the image sensor as a small slit, via a front and rear curtain. What this means is that during constant light, the image is being painted onto the sensor gradually from one side to the other as the shutter opening travels across the sensor. This, BTW, happens very fast. However, once you decide to add a flash to light the subject, only the area of the sensor exposed by the shutter at the time the flash fired will be exposed. The rest of the image will be dark (assuming there's very little ambient light on your subject!).
So what does this mean? It means that when using a flash, it's not the shutter speed that counts, but the maximum speed in which the entire shutter is open, therefore allowing a complete exposure of the image when using flash. This is what is known as the flash sync speed.
Back to my test. Both cameras were used in manual mode, as well as the flash. I started with the SB600 at 1/4 power to allow for plenty of power against the bright sun as well as quick recycle time. First things first, here's the published sync speeds of the camera bodies being tested:
Nikon D90: 1/200th second
Nikon D40: 1/500th second
Interesting that the lower priced D40 outperforms the highly coveted D90 by twice the sync speed. Chalk it up to the D40's electronic shutter.
So now it's time for battle. Did the bodies perform exactly as specified by the owner's manual? Sort of. I was pleasantly surprised.
The Nikon D90 did perform as promised. It achieved a perfect sync speed of 1/200th of a second. Of course, there are tricks out there that a photographer may use if the want to shoot outdoors in bright light with a wide open aperture. Such tricks include neutral density filters, such as the awesome but pricey Singh-Ray Variable ND filters. Nikon also offers FP (Focal Plan) mode in some of their camera bodies and shoe mounted flashes which sends out pulses of light which synchronize with shutters speeds up to 1/8000th of a second, thereby filling the entire sensor will light from the flash.
Back to our test! What about the entry level, D40 with the published flash sync speed of 1/500th of a second? When I tested the 1/500th shutter speed with flash, it passed with flying colors. So I decided to bump up the shutter speed to 1/640th of a second. IT PASSED! Wow! Very nice. Ok, let's try bumping it up some more to 1/800th of a second. IT PASSED AGAIN!!! Wow! That's a sync speed FOUR times faster than my beloved D90! Pretty cool. Of course I needed to try more, more, more. I needed to find the true limitations of this small wonder myself. So I boosted the shutter speed to 1/1000th of a second. It looks like this is where our limit was reached. I got a completely black screen. Still, 1/800 was pretty darn good in my book. The sync speed champ, Nikon D40!
Flash sync speeds tested using Gadget Infinity Cactus triggers and a Nikon SB600 in 1/4 power manual mode:
Nikon D90: 1/200th
Nikon D40: 1/800th
So why the big difference, especially since the D90 is considered to be a superior camera? The answer lies in the D40's electronic shutter. Once the front curtain of the shutter has traveled its course, a signal is sent to the camera to shut off its sensor. This is then followed by the rear curtain which covers the sensor completely. The Nikon D70 is said to have a similar shutter mechanism which also allows for sync speeds similar to the D40.
(Pictures will be posted soon)