Reviews
Glossary
The Nikon Creative Lighting System is a wireless flash trigger system built in to Nikon DSLRs and some Nikon Flashes (SB-600, SB-800, SB-900)
It works by infrared rather than radio (presumably to do with differing radio frequency laws around the World) which requires line-of-sight between the flash & camera (although it can surprise - it seems to work flawlessly with the flash in a softbox.)
The beauty of CLS is that you can set the flash outputs from the camera, putting the flashes into up to 4 banks, and using 3 different channels so more than one photog can work at a time. It's great being able to adjust flash output without having to go to each light and fiddle around inside softboxes.
Flash power can be set either absolutely, or as ratios against TTL metering.
Note how I said "up to" 4 different banks - when using the pop-up flash you only get 2 banks plus the pop-up. To get the extra you need to use an SB800/900 or the SU-800 ir commander unit.
As well as the line-of-sight issue, the other down side of CLS is that some light from the commander registers in the image even if you have set it not to contribute. It's only really noticeable as a catch light in the eyes, and it's fairly easy to block by making your hand on the lens a little "bigger".
I highly recommend the CLS system, especially as a way of avoiding purchasing wireless triggers like Pocket Wizards or CyberSyncs. Just be aware of its limitations.