>Dear Nikonians--need your expert advice. > >The concept is a picture of someone taking the last step down >a dimly lit spiral staircase, so that there is motion but the >figure is sharp at the bottom step. I have set my D90 to >Manual mode and Rear curtain sync and exposure based on >ambient light. I'm using an off camera SB700 in commander mode >(it fires just fine). My problem is that the figure remains >ghostly. I've tried overexposing--really ghostly!--and >underexposing--a bit more evident--but I haven't found a >setting that makes the figure sharp at the end of the step.
When there is motion in a flash picture the flash will stop the motion. However, if the ambient is bright, there will be a second image on top of the flash frozen image, and depending on the shutter speed, that ambient contribution may show the motion blur.
The only way to stop this blur is to eliminate the ambient portion of the exposure. So, the first step is to turn OFF the flash and shoot a picture using the shutter speed and aperture you want to use with the flash ON. This will show you how much ambient contribution you are getting. You want this to be very dark to eliminate the ambient.
To eliminate the ambient, you have to increase the shutter speed and you also may have to select a smaller aperture (high numbered f/ stop).
This is all best done with the camera in Manual mode, so you can adjust the shutter and aperture to whatever you want.
Also, make sure the flash is in Regular TTL and NOT in TTL-BL mode. TTL-BL mode is for adding fill flash to an ambient exposure, which is the opposite of what you are trying to do.
Then, when you get a totally dark ambient exposure, turn ON the flash and let it provide all the light for the exposure. Then, the motion will be stopped.
However, if the ambient is bright, there may not be any settings that will eliminate the ambient exposure. Then, the only solution is to turn OFF the flash and shoot the picture using the ambient light at a high shutter speed to stop the motion.