Nikon D50By: Dave Etchells and Shawn BarnettNikon develops an "entry-level" SLR loaded with features for less than $750. (Body only) <<Exposure :(Previous) | (Next): Shutter Lag & Cycle Time Tests>> Page 10:FlashReview First Posted: 05/20/2005, Updated: 08/10/2005 |
Flash
Built into the Nikon D50 is a pop-up flash unit, which operates in one of four modes: Red-Eye Reduction, Red-Eye Reduction with Slow Sync, Slow Sync, and Rear-Curtain Sync. Red-Eye Reduction mode pulses the very bright autofocus assist lamp before the main flash exposure, to reduce the Red-Eye Effect in shots of people. Red-Eye Reduction with Slow Sync works in a similar fashion, but combines the flash with a slower shutter speed for night portraits. (This reduces the harsh effect of nighttime flash shots, allowing more of the ambient illumination into the picture.) Slow Sync mode works with shutter speeds as slow as 30 seconds (!) to preserve color and background lighting effects in night shots. Finally, Rear-Curtain Sync fires the flash at the end of the exposure, producing light trails behind moving subjects, rather than in front of them. In all flash modes, the flash fires with every exposure. Closing the flash disables it completely. The Flash popup button to the left of the flash doubles as a Flash Compensation button, adjusting the overall brightness of the flash from -3 to +1 EV in one-third-step increments when the Exposure Compensation button is also held down while turning the Command dial. (That's a lot of button-pressing and turning, but I didn't find it all that awkward in practice.) Pressing the Flash popup button while rotating the Command dial cycles through the available flash modes.
The Nikon D50's internal flash is fairly powerful, with a guide number of 11 meters or 36 feet at ISO 100 (TTL Auto mode). That's a bit of an odd rating, given that the minimum ISO on the D50 is 200, but so many flash units are marketed based on their guide numbers at ISO 100 that Nikon doubtless felt a guide number rating at that sensitivity level would be the most meaningful to consumers. At ISO 200, the corresponding guide number would be 15 meters or 49 feet. This means that an f/2.8 lens will give you an effective range of about 17.5 feet, an impressive distance for an on-camera flash.
The Nikon D50 is also impressive in that its highest flash-sync shutter speed (the speed at which its focal plane shutter is fully open, permitting the flash to illuminate the entire sensor) is 1/500 second. This is very fast, makes it easier to emphasize the effect of the flash over ambient lighting, as well as to shoot fill-flash exposures with relatively large aperture settings under relatively bright lighting.
Also included on the Nikon D50 is an external flash hot shoe, just behind the pop-up flash compartment. The hot shoe accommodates Nikon accessory flash units, as well as a wide range of third party flashes. The full range of flash sync modes remains available for compatible flash units. Different Nikon Speedlights offer different features when used on the D50. The tables below (again used by courtesy of Nikon USA, Inc.) shows the features available when using various Nikon Speedlights with the D50. (Note that while many older flash units will work in non-TTL auto mode with the D50, but the full power of i-TTL is only available with the SB-600 and SB-800 models. Also, note that the SB-600 and SB-800 have powerful built-in autofocus assist illuminators that take over that function when coupled with the D50. With older flash models, the D50 has to provide its own AF-assist lighting.
3D Matrix Flash Metering
The "3D" aspect of the Nikon metering system is that it uses subject distance information from the lens (only available with D or G-type lenses) to guide its exposure decisions. This is particularly key with flash exposures, because flash illumination falls off quite strongly as the subject gets further from the camera. With 3D Matrix Flash Metering users don't have to give a second thought to balancing the flash with ambient lighting. Just snap a few test shots to see how much fill you want, decide what level you need (for instance, -2EV). Then set that level of flash compensation, set the flash to "fill" mode, and that's it. This is really a case of technology working perfectly in the service of creativity. The camera just quietly does its job, so you can focus on composition, color, interacting with your subjects, etc. It doesn't remove the creative decisions of how you want to light your subject, it simply removes the technicalities from the equation.
Wireless Remote TTL (iTTL) Flash
The D50 brings Nikon's unique "iTTL" wireless through the lens flash metering and control first seen on the D2H down to an entry-level d-SLR. When the D2H was first introduced, the phenomenal capability of iTTL flash operation actually struck me as a being a bigger innovation than the D2H itself.
Nikon has long been known for their 3D matrix metered fill-flash capability, and the exceptional ease it brings to fill-flash exposures. With iTTL (the "i" is for "intelligent" TTL), they're further extending the capabilities of their flash technology. In the D50, iTTL makes use of the 420-element RGB sensor used for the main exposure system, the accuracy of the metering pre-flash has been improved, and wireless capability has been dramatically expanded, with the implementation of true multi-unit, TTL wireless flash autoexposure. To me, that's the most amazing part of the new flash technology: Not just that it provides automatic flash operation without wires, but that it offers true Through The Lens (TTL) metering for flash exposures, even with multiple remote flash units: With an SB-800 speedlight as a master controller, up to three separate groups of SB-600 and SB-800 strobes can be controlled independently, each group consisting of an unlimited number of units.
Wireless TTL flash capability is one area though, where the D50 suffers somewhat relative to its big brother the D70. The higher-end D70 can itself serve as a master controller, although it can only control one group at a time, and its internal strobe can't contribute to the exposure when it's acting as a controller. The D50 lacks the ability to act as a master controller, instead requiring that an SB-800 unit connected to its hot shoe perform that function.
When I first heard about it, the whole wireless TTL system sounded like just so much magic, but it's actually pretty straightforward once you know what it's doing. (Straightforward, but no doubt requiring a lot of clever engineering.) The key to it all is strobe circuitry that can turn on and off very quickly, and fire multiple precisely timed bursts in a very short period of time. The iTTL system uses this capability in two ways. First, it uses rapid series of very brief pulses of the strobes to let the Master Controller "talk" with the various groups of remote units. The Master can command groups of remotes to fire either very brief pulses for metering, or more powerful flashes for the exposure itself. It does this by sending treating the flash head as a digital data channel, encoding commands about the type and intensity of pulse to fire in the form of rapid bursts of light.
The second way that the fast-pulse capability facilitates iTTL is by making it possible to determine exposure levels from multiple flash groups very quickly. (The speed is important, as you don't want the flash exposure determination to introduce an unacceptable shutter lag when working with multiple groups of speedlights.)
The way the iTTL system works is that the camera tells the Master controller to individually command each group of remote flashes to fire a metering pulse. Using its internal TTL sensors, the camera measures the amount of light coming from each strobe group, and integrates the light readings from all of the strobes with the ambient light coming through the lens. Via the Master controller, it then tells each strobe group how much light to emit for the exposure itself, and triggers them to fire when the shutter is opened.
If this sounds like a lot that has to go on before the shutter opens, that's because it is. It all happens very quickly though, without introducing an appreciable delay in the shutter release. (If you have several groups of strobes involved in a single exposure, and have quick enough visual reflexes, you can actually see a very brief period of flickering strobe flashes before the main exposure itself.)
The results are really pretty amazing. You can more or less scatter strobe units around the set any which way you want, and the iTTL system will deliver not only an accurate default exposure, but perfect control over the light being delivered by each group.
Given that the Nikon D50 can't itself act as a master flash controller, I won't spend any more time here describing Nikon's wireless flash system. Interested readers can refer to my coverage of the Nikon Wireless Lighting system in my Nikon D70 review, or in the Nikon Wireless Lighting video we made at the Spring 2005 PMA show, describing how we used a set of four Nikon flash units to capture perfectly-lit product photos with a portable setup.
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