kibbles304 Loc: Indiana

While using rear curtain flash with slow exposure, the flash is firing at the beginning of the exposure and then again at the end of the exposure. I've searched the internet and this site with no success. I have Darrell Young's "Mastering the Nikon D7100. I am either missing something or the camera needs to be repaired. Thought I would ask you guys first. I have thought about doing a factory reset but will wait till after I post this.

wdross Loc: Castle Rock, Colorado

Unless it is a super flash, rear curtain will only go off as the rear curtain starts to close. Normally, the flash goes off once the first curtain exposes the film or sensor. But unless it is a super flash (steadily flashes during the whole slow exposure), the flash will only fire once. If it is flashing twice, it is more than likely you have your red-eye reduction on. That is a pre-flash to get the subjects eyes to dilate small and contributes nothing to the exposure.

big-guy Loc: Peterborough Ontario Canada

When ever you fire your flash it always makes 2 flashes. The first is to judge the exposure and the second is to take the actual photo. It happens so fast you can't see the double flash. But when you move to 2nd curtain flash you can then see the pre-flash with the main flash coming when the 2nd curtain starts to close. It threw me for a loop the first time I tried as well as I'm sure almost all get fooled.

Note: red eye reduction is similar but then 3 flashes are actually fired. The first to adjust the eyes to close down, then the exposure judging and finally the main flash.

wdross Loc: Castle Rock, Colorado

Thanks for the information. It will help me if someone ask a question about such the next time. It makes sense once one thinks about it

GoofyNewfie Loc: Kansas City

Super flash?.... You mean High Speed Sync ( Auto-FP in Nikon Speak).

I concur that a pr-flash for red-eye or exposure could be what the OP is experiencing.
Going manual on the flash and turning off the red-eye reduction should eliminate the pre-flash.

speters Loc: Grangeville/Idaho

That is just not true, it only fires a preflash when using ttl/tti !

kibbles304 Loc: Indiana

No. the red eye flash is turned off. But, thanks for the response wdross.

kibbles304 Loc: Indiana

You are correct! Took flash out of TTL and put it in manual, the pre flash or first flash has stopped. Thank you so much speters.

kibbles304 Loc: Indiana

Thanks to all who responded. This site is a treasure of information.

wdross Loc: Castle Rock, Colorado

Olympus developed a flash mode called super flash. It is where the flash output is reduced slightly but is stretched out over a longer period of time to allow the flash image to record some subject movement.

GoofyNewfie Loc: Kansas City

Yes, I see now
Olympus calls it Super FP flash.
https://asia.olympus-imaging.com/product/dslr/accessory/flash/fl900r.html
Yet another term...
Been around quite a while!

GoofyNewfie Loc: Kansas City

http://www.ayton.id.au/wiki/doku.php?id=omd:flash_superfp

1980’s. Does this pre-date other systems?
I’ve always admired Olympus equipmentk

Shoeless_Photographer Loc: Lexington

If first curtain is selected, you'll see one flash when the shutter opens. If second curtain is selected, you'll see a flash when the shutter opens, and a second flash when the shutter starts to close. If you slow down your shutter speed to, say, 1/2 second or slower, you should be able to see the difference.

amfoto1 Loc: San Jose, Calif. USA

Rear (or 2nd) curtain flash cannot be used at the same time as High Speed Sync. If you think about it, they serve opposite functions. Rear curtain flash is used with slow shutter speeds, to cause the flash to go off at the end of the exposure. HSS is used with fast shutter speeds, faster than the native flash sync speed of the camera, shortening the duration of the flash and timing it to occur when the shutter is open.

iTTL (Nikon's term... it's called ETTL by Canon, other things by other manufacturers) is flash metered "through the lens" using the camera's built in metering system. In most cases it works by firing a lower powered "pre-flash" prior to the actual exposure and measuring that to calculate the power it will use for the "actual flash" exposure a moment later.

iTTL works this way with BOTH first curtain and rear/second curtain (as well as HSS). In fact, it works with any mode where you have the flash set to iTTL. In normal use this occurs so fast that you don't notice the flash is firing twice. But when you slow things down and are using rear curtain, it becomes more noticeable that the flash is firing twice. The pre-flash usually not any problem unless you are using the flash in conjunction with some other optically triggered devices (studio strobes, etc.), in which case the pre-flash will trip them too early.

When the pre-flash is a problem for any reason, simply take the flash out of iTTL mode and it will only fire once, a shot timed to coincide with the opening of the shutter. It can be front or rear curtain (or HSS) as you see fit for your purposes (but not rear curtain and HSS at the same time).

lamiaceae Loc: San Luis Obispo County, CA

And a treasure of disagreements it seems.