Hi,
I'm new to photography, and recently received an sb-910 flash(mounted ln D90).
As part of some nightly experiments, I've tried a long exsposure (15 seconds) with a rear flash.
Unfortunately, the device flashes twice, at the beginning of the exposure and at the end (TTL mode).
The user's manual is in German, which I don't understand.
Any thoughts?
Thanks in advance,
Onmri
You are using TTL flash mode and also Rear Curtain sync in camera.
TTL flash mode makes a preflash immediately before shutter opens, which is metered by the camera to set final flash power level for correct TTL flash exposure.
Rear Curtain sync waits until the end of the 15 second shutter duration to flash the final exposure.
So, you see two flashes. If it were normal front curtain sync, you would never notice.
First preflash is immediately before the shutter opens.
Normal Front Curtain flash occures immediately after the shutter opens.
Rear Curtain sync waits until the shutter is almost ready to close.
Rear curtain sync is used to to make trailed blur streaks from continuous light (due to show shutter speed, moving car lights for example) follow behind the light (naturally), instead of leading it in front (unnaturally).
Here is a sample:
http://www.scantips.com/lights/flashbasics5.html
Rear Sync does not otherwise affect flash exposure, which is extremely short duration.
It only affects When the flash fires, relative to shutter opening/closing.
English SB-910 manual is available in PDF file here:
Nikon Product Manuals available for download
But Rear Curtain Sync is a camera shutter function.
Rear Curtain Sync control is same camera button as Flash Compensation, but using the other dial wheel.
