I've never used a wireless flash - how exactly would it work? From Youtube videos I see that the internal pop-up flash on the D90 still goes off at the same time as the SB600.
Is it possible to have just the external SB600 go off, but non the pop-up?
The Nikon wireless flash system is called CLS, and although it is an extremely deep subject that you can probably read up on elsewhere, here's a basic overview:
The D90 is sending pulses of flash
before the actual exposure and the flash of the SB600. It happens quickly, so you think they all go off at the same time but in reality the D90 pulses are over when the exposure is taken, leaving just the light from the SB600 in the picture. I don't know the exact details but the pulses tell the SB600 how strong to fire and when, etc. Using this system you can then control the power of the SB600 from the D90 without having to go over to the SB600 and set it up. Also there is this thing called iTTL mode which is kind of like metering for flash, the flash can somehow (unclear to me) determine what the proper power is to correctly expose the subject in the viewfinder, or you can just straight up tell the flash to fire a manual burst (full power, half power, etc).
The triggering is actually done via infared light so there is an optional accessory that goes in front of your D90 flash that blocks the visible light but lets the IR through, and cuts out any residual flash from the D90 pop-up flash in the picture.
The advantage is that any camera (D90 or higher) can act as a commander and you can use the built in flash. The disadvantage of optical triggering is that it is line of sight based, so your remote flash has to be able to "see" the pulses or it won't fire. If it's behind some obstruction, or too far away, it won't work. You can also use most of the flash units themselves (basically any current Nikon flash except the SB-600) as commanders, if you need more power than your built in pop-up can provide, or if your camera does not have the commander ability built-in. Obviously if you are using an external flash mounted to your camera as a commander, you will need a second (or more) flash to position remotely.
Another advantage is that you can control multiple sets or "banks" of flashes at once. So you can set one flash to be one power, another flash to be a different power (to light the background, etc) all from your camera without having to move. The higher end equipment (SB900) can control up to 3 banks, the lower stuff like the D90 or SB700 can control up to 2.
If you need greater range, or can't have line of sight, you can get radio-based wireless triggers. The drawback is that most of the cheap ones can't do the iTTL metering so you can only run in manual mode, and I think you are limited to one bank. However, there are some newer wireless triggers (I think PocketWizard makes the most advanced ones?) that support iTTL and everything. The drawback is that these units are expensive. But they are much more capable as far as range or placement goes.
Anyhow it's more than enough to get a single SB600 or SB700 and just play with the built-in commander on your D90. You can always add more capability later and that first SB600/700 you buy will still be useful, so it's not really wasted money.
I say all of this because I am myself very interested in the SB700 as my first flash too. I have never really shot with flash much in the past, mainly because I only have the built-in flash on my D80, but think it would be useful and interesting to learn some basic lighting techniques with a single (off-camera) flash.
A
great site for learning some off-camera flash basics is the strobist website:
www.strobist.com. They are really into doing things manually and using older (cheaper) equipment, but much of the basic theory applies should you still decide to go with the convenience of the CLS system.
Ruahrc
