The instruction manual of the SB-700 is available for download now from Nikon, and I could finally have a look at the guide number table. Before, all that was known was the GN at 35mm FX, and sadly that GN of 28 (m) is lower than the one of the SB-600 (GN30) it replaces.
But in contrast to the 600 there is sensor size detection available on the SB700 now, which means that it does not zoom to the 50mm reflector position when a 50mm lens is used with a DX camera like the D7000 or D90, but it zooms to around 70-75.
SB-700 Guide Number with FX Cameras
Click on the image to see a full size version of the guide number table showing the SB-600 next to the predecessor SB-600. Both flashes cover down to 14mm with the built in wide-panel for standard illumination. With the optional center weighted illumination, coverage extends to 12mm.
At the tele end, the SB-700 reflector ends at 120mm, whereas the SB-600 ends at 85mm already. However, the SB-600 is stronger by design and there is no focal length with an FX camera body where the SB-700 would be advantaged, neither at wide angle nor towards the tele end. SB-600 is always a stronger flash.
SB-700 Guide Number with DX Cameras
With DX cameras the situation is different. Depending on the zoom setting the flash gains the ability to chose a more narrow zoom position. With the 50mm lens, the SB-600 will zoom its reflector to 50mm. The SB-700, however, will zoom to around 70mm reflector position and still cover the full frame while gaining a bit of power – or wasting less light.
Click on the table to see the details for different zoom settings and SB-600 versus SB-700 in DX zoom mode.
The following chart shows best the benefits of DX zoom on a speedlight, at least if you are using a camera with APS-C image sensor. From the 50mm lens setting on the old SB-600 is still advantaged, but at lens settings 35mm and lower the new SB-700 suddenly is the stronger flash of the two!
I still don’t like the recent Nikon trend of making their latest speedlights weaker and lower in maximum output than the previous generation, and if you’re using an FX body like a D700 you just have less juice than before. At least, for DX shooters, the sensor size detection flash zoom feature helps mitigate the issue and can give you even an advantage.
And, overall, the SB-700 is a big improvement overall with much better ergonomics, an optical slave mode, the wireless master mode, and lots of other advanced features.
Speedlight specs comparison page with data on all Nikon flash models from 1988 plus selected Canon, Metz, Nissin, Vivitar and Yongnuo flash units.
SB-700 available now in US!