Moving along with my hands-on on the Nikon D90, I moved into flash photography today. My first impulse was to turn off that auto ISO limit and moved it all the way down to LO.1 (or ISO 100). Facial hairs, reflections on the pupil of my portraits became apparent and natural, utilizing bounced flash for each of those shots.
Again, as I said, its a hobby and I intend to keep it that way. SB-400 is good enough for me. With an effective range of up to 60 feet, NEF images on my Nikon D90 appears analog-film clones. Installing one is a snap. The D90 automatically detects it and control it for each shot. Rear sync flash becomes fulfilling once again.
But do still bring your tripod along for nightscape as flash doesn't work in those shots. Here's a rough guide table for your flash shoots
The SB-400 flash unit supports improved Though The Lens (iTTL) balanced fill-flash feature, FV lock, flash color information communication, rear curtain sync and red-eye reduction on the Nikon D90. Flash Value (FV) lock is the ideal tool to take out-centered subjects in dark backdrop with the intent to bring out the background detail. The AE-L/AF-L button can be configured to activate this function on demand. Please remember to switch E5 custom menu item to ON to enable Auto FP high-speed sync to take shots with varying shutter speeds of 1/200 to 1/4000 second. I encourage you to know all about flash photography [here].