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Rear-curtain sync

From: Foundations of Photography: Flash

Video: Rear-curtain sync

In the last movie, you saw how we could combine Yup.

Rear-curtain sync

In the last movie, you saw how we could combine a slow shutter speed with a flash to get an exposure that a well exposed foreground thanks to the flash and a well exposed background thanks to the long shutter speed. Now, the thing about a long shutter speed that you're probably already used to is that a long shutter speed allows you to create motion blur. So, is there a way that I can use that motion blur in an image? A, a low light image with a flash to create any kind of effect. Obviously I wouldn't be asking that question if there wasn't. Have you ever seen an image that looked like this.

I've got this wonderful streak behind my subject, but the subject is frozen. That streak is coming from a slow shutter speed. The frozen image is coming from the flash, so this is a slow sink image. The trick to it is I need to control when the flash is firing. If it fires at the beginning of the image, then they are a still image with a blur on top of them. If I fire them at the end, then I get a blur with them at the end. This is going to all make more sense as we create a shot like this. So I'm not sure if you noticed, but there's a guy on a unicycle riding behind me.

I didn't notice it at first, and then I turned around, and lo and behold there's a guy on a unicycle. This is Nick Brazzi, who is a I didn't know this until today, an incredible unicyclist. Just to add a little tension to the movie here, we're just going to see how long he can go. I'm just going to take my time and he's just going to go back and forth. Yup. Yeah, and we'll just see if he wears out. Anyway, our other goal is to get a shot of him riding. Now, you might also have noticed that we're standing in an empty warehouse. Here is part of the thing with this kind of effect. You, it's a very delicate balance of lighting effects that we're going for here.

We need a dark background, because motion blur is translucent. If it's in front of something really bright, you're not going to be able to see it. So we need a dark background, or we need to do this in very low light. So we're in this darkened warehouse here. So, I'm just going to take a picture, and we're going to build this up and see what happens. I think you're going to find, when you go out to do this that you're going to run into the same problems I have. You're trying to find this balance of the right amount of blur to create the length of streak you want, but some exposure setting troubles that you gotta wrestle through to get everything to look clear and, and saturated and everything.

So, I'm going to just start here. It's low light. I know I'm going to need a little more ISO so I cranked my ISO up to 400. I also know that nothing auto is going to work in this situation, so I'm putting my camera in manual mode and the first thing I'm going to do is slow my shutter speed down. I'm just going to set it on one second. And the reason I'm slowing the shutter speed down is I need time for him to get across the frame. So he's got about a second worth of blur, I hope. So we're going to see what happens. I'm going to just frame up a shot here. Now, the next problem is I need to auto focus. I need to auto focus before he gets in the frame.

And I can't do that because he's not in the frame. So, I'm going to first take a pass here, and let him get in the frame. And, now I'm going to auto focus and now I'm going to switch my camera to manual focus for the rest of my shoot. As long as our distance to each other doesn't change, my shots should be in pretty good focus. So, now... That stabilized the camera, and I'm getting this. I'm going to turn the flash off. Here's what I got, and it's too much information all at once. I got flash in there, that's confusing things. I want to just figure out length of the streak here, so. So this is one second. That's pretty good.

I'm getting nice saturation on him on, on color saturation on him, the streak is really burned in. I can tell you the reason the streak is burned in is because we've set up some extra light. We've got a light down there shining this way and he's riding back and forth through that. The thing is, for his blurry self to register on the image sensor, it needs to be reflecting a lot of light. When we first came in here, it was just too dark. We weren't getting blur. So, again, you're looking for the right combination of lighting situations here. I'm not saying, so, if you want this effect, you gotta carry a light around with you.

What I'm saying is that you probably will find best results when you are somewhere in low light, so there's a good, dark background, but there's also other light around that's hitting your subject. So that's a pretty good streak. I can control the length of it by changing my shutter speed. So I'm going to go down to a second and a half, take another shot, and that's too long. He's actually passing all the way through the frame. So I'm going to back off a little bit. A second and a third. I'm trying to stabilize the camera as much as I can. I'm waiting till the moment he enters the frame.

I'm pressing the shutter button. Okay, that's pretty good as long as he rides at that speed. We've got a good amount of blur. Now, the problem in this image is he's just all blur. I want that frozen bit of him, so I'm going to turn my flash on. I don't want TTL metering here. I don't trust the flash in this situation because it doesn't actually know what I want. Let me show you what happens if I do a TTL shot here. I get this, now, the first problem I've got is that the flash is firing as soon as I press the shutter button, and so you can see that the more solid version of him is right at the beginning of the blur, we want it at the end.

Now, you've learned already, that when you press your shutter button the first curtain of your shutter opens, the flash fires, the second curtain closes. I can tell the camera to wait and fire the flash right before that second curtain closes. That's called second curtain sync. Depending on your system, you may be able to activate that from your camera. I'm using a Canon system. I cannot do that from the camera. I have to do it from the flash. There is a button on my flash. If I press it, I go into high speed sync mode, which is not what I want. I press it again and I get this icon which indicates second curtain sync.

Your flash may be completely different than that. Just look in your manual for second curtain. Second curtain sync, slow sync flash. Any of those are going to lead you in the right direction. So now I'm going to wait for him to come back through, and my flash, you may see a couple of flashes here. The first ones going to be a metering flash, the second one is the actual flash that fires. That's looking better, now I've got a more solid version of him right there at the end. It's a little over-exposed though. The flash is firing too much again. TTL metering doesn't have the foggiest idea how to handle this situation.

So, I need to take some manual control and figure out how to get my flash set manually. That could take a while. How you doing Nick? Alright, he is doing fine. Okay, so I am going to punch my flash over to manual mode and then, on this flash that's just simply pressing the mode button. So now I'm in manual mode. I'm at full power. That's one to one. So, now we'll see what the flash throws in to the scene. I'm also keeping my left eye open. It's when I press the shutter button the shutter's going to close and I need to make sure the flash is firing. So I'm keeping my left eye open so I can see when he enters.

I can see if the flash is fired. And here's what I get. Okay, this is looking better. It's still too hot, but I am noticing that I like the shots better when he's riding that way, because he's riding into the light, so the front of him is all lit up. So I'm going to start only shooting him going left to right from my perspective. Flash is too hot. I've got a few different options here. I could turn down flash power, or I could turn down my aperture. I think I'm going to go with turning down the flash power, because the flash is going a long way back there.

And I'm, I would like my background to stay darker. This may be entirely the wrong decision, I don't know, but this is how you just feel your way through these situations. So, I'm in manual mode. All I have to do here is dial down, that's half power. You know, I'll go a little bit further. I'll go down to quarter power, so that's two stops. Two stops less flash power. All my other exposure settings are staying the same and we'll see what happens. Again, my auto-focus should still be okay. Okay, that's good. It's not really changing my background very much.

So, I think what that means is the flash is not actually hitting that back wall back there. What's making my background bright is the long exposure time and there's no way around that. I need the long exposure time to get the blur. I need to check my histogram here, because it looks like there's overexposure. Sure enough, I'm getting a spike over here on the right hand side of my histogram. That indicates I'm getting near overexposure. I'm not seeing any flashing highlights here, so there may not be. Still, I would like it a little less hot. So, I'm going to turn the flash down some more. I'm going to go down another stop.

And go to one eighth power. Ideally, I would be doing this on a tripod but this is such a stylized image. I'm not that worried if there's a tiny bit of shake and he's going to be such a compelling thing in the frame. And I think it'll upstage any slight motion blur there is in the back. ha, that's coming along. It's less hot now. The problem is, he's not real opaque. And I'm wondering if that's because I've turned the flash down. I'm not sure.

So I'm going to turn the flash back up. I'm going to turn it back up to half power and I'm going to turn my, I'm going to close down my aparture, that's going to dim my flash a little bit. I may be just getting, I may just be ending up right back where I started. I'm not sure. But my idea here is if I hit him with a lot of flash light right at the end maybe it'll give me a good solid exposure of him. So I just need to wait for him to come back to left or right. ha.

Yes, that is working. So the image before he also ended up right in front of that pole. You can kind of see through him on this image. He is a lot more opaque, which I am sure is good news to him as well. I'm going to go down a little bit more though. I am going to go all the way down to F11. I am keeping my shutter speed the same. And I'll just wait for him to come back by. So, again, if that didn't make sense to you, the idea here is I'm, I'm trying to get good strong flash exposure on him right there at the very end to get a really solid exposure of him. My slow shutter speed is giving me some nice blur before then.

This looks good. His face is still a little bit hot. I think I can pull that down in post-production. I really like what his shoes are doing also. So, again, we've, we've brought in our own lights for this situation. You're not always going to have to do that. What you're seeing here is that you want this particular relationship between a good amount of light for your subject, a dark background so that the translucent parts have something to show off against, and then its a matter of, as with any flash picture, balancing your flash exposure against your ambient exposure.

However, in this case we want the ambient exposure. To include a good motion blurring slow shutter speed. So, you saw me play with shutter speed first to get the amount of streak that I want. And then it was a matter of playing with flash power and aperture to get that relationship that I wanted between foreground and background. But the most critical thing for this particular effect is that I want him, the frozen version of him to be at the very end of the frame. And that was achieved by setting rear curtain sync in my flash.

As you probably imagine from watching this, this is something you gotta practice. It's something you gotta experiment with. Don't expect to run out and grab something really quick. This is something you need to go play with. You need, usually, a fairly slow moving subject. They need to be in the frame long enough to burn an image into the sensor. Increasing ISO can perhaps make that go faster, but you're just going to have to experiment and feel your way through it.

Show transcript

This video is part of

Image for Foundations of Photography: Flash
Foundations of Photography: Flash

40 video lessons · 17179 viewers

Ben Long
Author

 
Expand all | Collapse all
  1. 1m 35s
    1. Welcome
      1m 35s
  2. 33m 1s
    1. Exposure revisited
      2m 22s
    2. How flash works
      2m 12s
    3. Balancing ambient light and flash
      3m 54s
    4. Shutter speed, aperture, and flash
      4m 11s
    5. Fill and key light with flash
      4m 13s
    6. Understanding flash range
      2m 47s
    7. Understanding flash modes
      5m 16s
    8. Flash sync options
      3m 2s
    9. Some notes about your camera's built-in flash
      5m 4s
  3. 32m 50s
    1. When to use fill flash
      1m 39s
    2. Using fill flash in auto and program modes
      2m 44s
    3. Fill flash in priority or manual modes
      2m 38s
    4. Using flash exposure compensation
      9m 14s
    5. Using fill flash to eliminate unwanted shadows
      5m 46s
    6. Using fill flash to darken a background
      5m 1s
    7. Using flash to supplement ambient light
      3m 48s
    8. Filling in for a bright sunset
      2m 0s
  4. 33m 53s
    1. Shooting a portrait with flash as the key light
      4m 27s
    2. Why use an external flash?
      3m 34s
    3. Flash power and recharging times
      4m 21s
    4. Flash zoom
      1m 45s
    5. Taking the flash off camera
      5m 35s
    6. Using a softbox
      5m 3s
    7. Balancing flash and window light
      4m 22s
    8. Paying attention to the light in the room
      3m 39s
    9. Flash and white balance
      1m 7s
  5. 54m 20s
    1. Bouncing flash to improve lighting
      13m 8s
    2. Alternative options for bouncing flash
      5m 12s
    3. Using slow sync with flash
      8m 50s
    4. Rear-curtain sync
      11m 54s
    5. Using radio controls to fire a flash
      4m 32s
    6. Working with manual flash
      10m 44s
  6. 25m 16s
    1. Building up to multiple flash units
      13m 3s
    2. Adding the second flash for fill
      5m 19s
    3. The third flash as a backlight
      6m 54s
  7. 7m 50s
    1. Which brand of flash should you buy?
      1m 27s
    2. Guide number considerations
      3m 13s
    3. Shopping recommendations
      3m 10s
  8. 42s
    1. Next steps
      42s

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