Rear Curtain Flash

[Jackie Schuknecht]

I was intrigued by Jaspar's Avian image of the week, and I was wondering what the difference is between front curtain, and rear curtain flash? Why would he have used rear curtain in that shot. Does it give it a certain look?

[Mike Milicia]

Here's my attempt at a short answer without getting into too much detail. The flash will typically only fire for a short time relative to the length of time the shutter is open. The flash is a very short duration and will light up dark areas of the the scene and freeze motion resulting in a sharp image. However, motion that occurs when the shutter is open but flash is not firing will likely blur. With front curtain sync, the flash fires as soon as the shutter opens, and then the shutter stays open for the set duration after the flash fires. With rear curtain sync, the shutter opens for the set duration and the flash fires immediately before the shutter closes. The main difference in effect between the two is whether any motion blur appears before or after the sharp image created by the flash. Imagine using flash and a slow shutter speed to photograph someone walking through a dark room holding a lit candle. With front curtain sync, the blurred light trail from the candle will be in front of the person (who will be sharp since the person was only visible when the flash fired and the flash was short enough to freeze the motion). With rear curtain sync, the light trail will be behind the person. The rear curtain effect seems most natural and that's probably why he used it although there's not a lot of motion blur in that particular image anyway so it may not have made a dramatic difference.

[Jackie Schuknecht]

Thanks for the detailed explanation Mike. Really easy to understand!

[Kevin Hall]

Rear curtain synchronized flash and a slower shutter speed does interesting things with hummingbird wings.

Broad-tailed Hummingbird image (http://4mallko.smugmug.com/gallery/5355531_ApiAv#334343257_ZSvkf-X2-LB)

[Mike Milicia]

Rear curtain synchronized flash and a slower shutter speed does interesting things with hummingbird wings.


Very cool image ... I like the effect!

Since there is no hint of motion blur of the body, I'm assuming that the bird was hovering.
If this were the case and if I understand things correctly, I don't think front curtain sync would have looked any different than rear curtain sync.

[Kevin Hall]

Hi Mike,

Front curtain would have been reasonably similar except you would have the flash stopping the action (providing detail in the wings) first and then wing blur on top of the stop action. With rear curtain stopping action after the blur the effect is a bit cleaner.

I'm glad you liked the image, it is not an easy one to make but I thought I would share the idea. As Jasper's image shows, rear curtain sync is a great tool with much potential and should be explored thoroughly.

[Jackie Schuknecht]

Interesting Kevin and lovely shot, thanks for posting more info.

[Ray Rozema]

Wow! Thanks for sharing