Beginner First curtain flash sync & Second curtain flash sync.

[Mclovin101]

Im trying to get my head around First curtain flash and Second curtain flash

Has anyone got any good examples of information on it

Thanks

 

[CraigDHD]

I'm sure google will be better but basically your camera shutter has two "curtains", when you fire the camera what happens is the first curtain moves exposing the sensor then after a delay the second curtain moves hiding the sensor. The flash syncs with the shutter so that the flash appears when the frame is fully open to give an even exposure.

Flashes have a sync speed which is the shortest duration the sensor is fully revealed for. As the shutter speed gets slower it allows more of a window during which the flash can fire.

With first curtain the flash fires as soon at the first curtain opens. with second, or rear, the flash fires immediatley before the second curtain closes.

The main use for this then is when you use flash with a slow shutter to introduce ambient so you can control whether the flash lights the start or end of the exposure.

In its simplest form using it with motion the flash will freeze and the ambient will blur. So with first curtain the blur will happen over the frozen part however with second the advantage is the blur will be behind and under the frozen part. The disadvantage with second is if there's movement you have more risk of losing focus.

 

[Nawty]

So by way of example, say someone is walking towards you in in dim light that required a slowish shutter speed.

First curtain flash would give you a clean image of the person at the start and then a blurry ghost trail in front of them.

Second curtain flash would give a blurry ghost trail leading up to a clean image of the person, so it looks like they've walked to where the photo was taken.

In most instances the second curtain flash gives a much better effect.

 

[HoppyUK]

Im trying to get my head around First curtain flash and Second curtain flash

Has anyone got any good examples of information on it

Thanks

Good link here, from Neil van Niekerk http://neilvn.com/tangents/first-curtain-sync-vs-rear-curtain-sync/

Bear in mind that second-curtain sync doesn't work at shutter speeds faster than 1/30sec, even when enabled. The camera defaults to first-curtain sync at 1/30sec and above, and best results are had at significantly longer speeds than that. There are some downsides to be aware of and it's often not the magic bullet that some users seem to think it is Knowing how a focal plane shutter works is helpful, and will explain what's going on.

 

[Phil V]

There's a lot of misinformation and misunderstanding surrounding this feature. But it is really simple.
Youtube shutter

You need to firstly understand how flash sync works. The reason your flash has a max sync speed is that as your first shutter curtain travels down the frame to reveal the sensor to the light, the second curtain follows to cover the sensor (or film) back up. At faster shutter speeds, the sensor is actually exposed by a slit between the curtains. At sync speed and slower, the whole of the sensor is seeing the image - it's at this point the flash fires to illuminate the image.
Between x sync speed and 1/30 sec, there's no real difference between 1st and 2nd curtain sync, because the shutter isn't really open long enough to register enough of a difference.

Below 1/30 second though, using 2nd curtain sync the flash fires just before the 2nd curtain comes down. So a linear moving subject would have a flash lit image with a faint tail illuminated by the ambient.

What it doesn't do (and is often suggested) is 'stamp' the flash image over the ambient image, in fact unless you're after that specific effect, 2nd curtain sync is a bit pointless.

I use long shutter speeds with flash quite a lot, but because my subjects don't have a linear movement I use 1st curtain sync. I do this so that I can still choose the timing of my shot (how random is it pressing the shutter knowing your final image will happen half a second later)

edit to add - most of this has appeared above - I was busy