You can use the SB-600, SB-800, or SB-900 as wireless flash, controlled through infrared (requires line of site of the sensor on the flash, or near a wall the signal can bounce off).
SINGLE REMOTRE FLASH SETUP
Switch the flash to remote (see the manual for the SB-600 menu).
Leave the default as group A. There can be multiple flashes in groups A, B and C. The purpose is you might want to set group B to +1EV to be twice as bright as group A.
Leave default as channel 1, of possible 4. I set to 3, so to not interfere with other photographers and their flashes.
On D7000 or D90
\Custom settings menu
TTL is the default (refers to built-in flash or attached external flash).
Choose CMD (commander) mode.
Put group A as TTL and built-in flash as double dash — for off. Press OK button (pressing anything else to exit the menu doesn’t save the settings).
The built-in flash needs to be up for the wireless flash to work, since it acts as a pre-flash and does not appear in the photo.
Alternately, set group A remote to Manual. 1/1 is a good starting point, you can then figure “okay I am about one stop (1EV) too bright so I can go to 1/2 power, or move the flash further away, or set the aperture darker by one stop om f/4 to f/5.6.” Or that “1/1 power is too weak, so I must move the flash closer or double ISO from 200 to 400.
Again, press OK to save the change to power as 1/2 or 1/4 etc.
You can add an additional wireless flash to group A, B, so you have two wireless flashes triggered by the built-in flash.
MASTER AND REMOTE FLASH SETUP
In the above basic setup, the built-in flash of the camera can be a pre-flash, not in the photo. If it was On (as a strong/main or a as a weak/fill flash) then it would be the master while the wireless flash is the remote.
If you have two flashes, you can have the SB-900 or SB-800 as the master flash on the camera; plus SB-900, SB-800 or SB-600 as a remote flash. The advantage is that the master flash will not be limited by the sync speed of the camera (see end of article) and also you get to use the flash’s red AF light cross-hairs to focus in low light rather than the camera’s light bulb (which is obscured by the lens in the way). This cross-hair appears even when the external master flash is set to not fire with –.
Put the SB-900 or SB-800 in master mode. It does not matter whether the camera has been set to TTL or CMD mode, or what the numbers are in CMD – the settings on the master flash’s screen override this.
So on the flash’s menu, set the on-camera flash to TTL or — (off), or even MANUAL by using the Mode button. Press the top left button to go to the next line and set group A to TTL or MANUAL. The buttons of the menu take a while to get used to, so again, read the flashe’s manual if you are stuck.
How I use this set-up practical – I like to have the SB-900 on-screen menu as my master flash on TTL 0EV to balance with the the remote SB-600. Or maybe master as -1EV or -2EV, if I want it to fill in the remote main flash to light a group photo evenly . Or master flash off, if I want the harsher look of a lone remote flash. I set the remote SB-600 to TTL 0EV. I sometimes to the diffuser dome on the SB-900 and a mini softbox on the SB-600.
CONTROLLING TWO EXTERNAL FLASHES MANUALLY
When using my flashes for a portrait shoot rather than a party, I put one or both flashes on stands with umbrellas or get an assistant to hold one. In this controlled situation, I set the main remote flash on MANUAL as 1/1 power on the camera’s menu. Then I see what I need to do regarding ISO, aperture, flash distance from the model, and diffusion (losing about 1 to 2 stops when shooting with an umbrella). I prefer to use the flash at 1/8 or 1/4 power, so that it recycles quickly, my batteries don’t run flash quickly and the flash doesn’t overheat (the SB-900 has a thermometer warning come up and it stops working).
Once the main remote flash is set, I introduce the second remote at maybe 1/4 power as a fill.
NOTE ON SYNC SPEED
Sync speed is the shortest possible shutter speed a camera can use with flash. For the D90 it is 1/200 (with Focal Plane FP high speed sync set on in the menu), D7000 1/320 (set as 320* in a menu for FP sync) and I believe it is 1/250 for D700 etc.
The built-in flash working alone means that the shutter can’t be set to 1/250 on the D90, even in shutter priority mode. In bright daylight, this means you aperture will be f/13 or similar – which means your small built-in flash will be very weak even lighting up something 2 metres away, and it also means you can’t do any artistic looks with the background blurred at f/2.8.
You can look up more details on high speed sync if you want, but it means that an external flash on your camera allows you to shoot as your camera’s limit (1/4000s on D90 and 1/8000 at D7000) by pulsing the light instead of doing a single burst (which is when the black bars appear from your shutter). This means you can shoot at apertures like f/2.8 with flash even in bright sunlight (since 1/200 f/2.8 would be severals stops too bright). The drawback is a loss of a few stops of flash power, depending on whether you are at 1/500, 1/1000, 1/4000 etc. If you can get the flash close to the subject, this is not really a problem.
If you put the built-in flash as a pre-flash as “–” with a remote on, you can use the remote flash with the FP sync option. If the built-in camera flash is on and you are shooting with remote flash again, you are limited to sync speed like 1/200. Anyway I don’t use the built-in flash as a or 3rd flash with my 2 wirelessflashes, since the quality of the light is still harsh and direct unless it’s used as a just noticeable weak fill.