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Lighting 102: 7.0 - Time-Based Variables

Way back when, we talked about the idea that you could balance your flash and ambient light levels by leaving the shutter open long enough for the ambient light to burn in.

But during that "burning in" time, there are also lots of things you can do to add layers of interest to your photos. And that is exactly what we will be covering in the last unit of Lighting 102...

The beauty of altering your camera's settings, focus, focal length or position during a flash/ambient exposure is that you can merge two completely different sets of circumstances into one single frame. It's a little like in-camera Photoshop -- with a nice, creative randomness attached to it.

Today, I want to go through a few of the ways in which you can manipulate your photo during burn-in and show some examples of the end results.

Flash and Pan

For this shot of a soldier in the woods near Ft. Meade in Maryland I based my exposure on the ambient light level. The first value chosen was the shutter speed, which was chosen to create the best pan effect.

Having chosen the shutter, that also gave us the aperture for the proper exposure. Then, it is just a matter of adjusting the flash to the correct power to light Robert's face.

So, why even use flash at all?

First of all, because the flash adds a nice margin of error to a pan shot. Since the flash happens instantaneously, it will freeze your subject. This works best if the background is brighter than your subject. If you expose for the background, your subject will be dark -- and ready to be frozen by the flash without any ghosting.

Second, it gives you control over the relative exposure level between the subject and background. I could have raised or lowered the background level, for instance, without changing the tonal values on Robert's face.

(More on how this photo was made here.)

For this shot of an up-and-coming local hip hop artist, I spent a few frames grabbing a flash/pan look even though he was not moving during the exposure. It was an assignment that appeared to be doomed form the start, so I was grasping at straws.

(Perversely, I kinda enjoy the challenge of situations like that. As long as they do not happen all of the time.)

The top frame is a static shot, and this is the panned version. The rapper (who performs as "Bossman") had just been signed by a record label and his ego was in overdrive.

I am sure he thought he deserved to be surrounded, nonstop, by a dozen of those dancing hotties from MTV and BET. And as such, was far too cool to waste his time on a lead photo in the Features section in the local metro daily. So (once I pried him out of his living room) anything I wanted to try for variety had to be done without changing the setup.

But even when pinched for time I am always looking to burn a few seconds trying something different just to see what it looks like. And even if this one did not work out very well (we went with the still version) the point is that a quick change of the shutter speed and moving the camera could give me a second look -- without wasting any more of His Majesty's precious time.

(You can read more about this blood-from-a-turnip shoot here.)

Will it Go 'Round in Circles

Another way to add an abstract layer is to rotate the camera during a flash exposure. When I am shooting with just a point-and-shoot and built-in flash, this is sometimes the only way I have to amp a flash-lit photo.

In this shot of Danny Ngan owning Chase Jarvis on Guitar Hero, rotating the camera during a flash exposure helped to make the background a little more abstract.

Whether you are panning, or panning or rotating, you want to begin the action before you press the shutter. This will give you a smooth effect, without the jerkiness that happens if you wait until you start the exposure to start the movement.

As before, it also helps if you are working against a brighter background.

Diffuse the Situation

Using time as a variable during a flash exposure does not necessarily mean moving the camera, either. You can shoot one portion straight and the other portion heavily diffused, for instance. Or filtered. Or both.

In the "Winter Book Club" assignment show at left, I started the exposure by firing blue-gelled flash from the back while there were about eight layers of plastic wrap over my lens. Then I removed the diffusion and finished the exposure painting with the modeling light on a second SB-800 with a CTO gel attached.

All of this has to be done in a darkened room, of course, or you will get (unwanted) burn-in from the ambient light. You can see more detailed look at how this photo was made here.

By now, you should be starting to get other ideas on how you can use time to manipulate your images while they are still being formed. You might, for instance, choose to light someone against a sunset and the defocus the camera during the ambient portion of the exposure. If you need for the image to stay in register during the process, a tripod is obviously a big help.

NEXT: L102 7.1 - Flash Zoom and Stone Soup


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Anonymous Nathanael Gassett said...

Great post, Sir!

I wanted to do a shoot today, and was about to settle for back-flashing Gatorade bottles, but now I have some new tricks to experiment with. Whee!


August 25, 2008 1:55 PM  
Blogger Trent said...

Another technique I use doing a push or a pull zoom while the shutter is open. Not the greatest example perhaps, but first I could find:
It's just like panning or rotating, but your zooming in or out while the shutter is open. Works best with camera set to first curtain sync, because you have your shot composed. If you sync to rear curtain, you'll have zoomed away from your original composition and not sure what you'll get. Of course, sometimes that random-ness can be a wonderful thing. Sometimes, it sucks.

August 25, 2008 2:30 PM  
Blogger Trent said...

...okay, so I should read through to the end of the post before commenting...

August 25, 2008 2:33 PM  
Blogger Andrew Kraker said...

LOL, I get the feeling you didnt really like the photo shoot with the rapper.

August 25, 2008 2:36 PM  
Blogger Michael said...

Last month I helped a friend of mine get an interesting time-based shot on film. We shot a traffic signal such that all three lamps were properly exposed. The ambient was really dark even at the 5.5s exposure needed, so I had to pop a flash to bring the lamp housing into the exposure a bit more. That also froze the motion on the tree behind the signal so it wasn't just a big blur from the wind.

Unfortunately, nobody thinks anything of the shot unless it's explicitly explained that it's a normal operating signal and there's no Photoshop involved. Oh well... we thought it was fun.

August 25, 2008 4:12 PM  
Blogger Chris said...

Correct me if I'm wrong, but couldn't you get a lot of these effects by using your second curtian sync option?

I shoot in ETTL (wireless transmitter), so I don't know if pocket wizards are capable of doing this as well.

August 25, 2008 4:19 PM  
Blogger David said...

@Chris (4:19pm)

I am doing this full manual, most of the time.

Typically, I prefer front-curtain flash, because it lets me choose the moment I want to freeze, rather than have to anticipate it by 1/8 (or 1/4, 1/2, 1/30th) of a sec.

When panning, flash-dragging or rotating, there are enough variables as it is, given that you have to start your movement before you fire the camera.

There are enough variables involved that it can be a bit of a learning curve at first, but the sprites and fairies that tend to work their way into your photos as a result are worth the low batting average, IMO.


August 25, 2008 4:37 PM  
Blogger illustratoranswers said...

I was fooling around with that this weekend actually. I was prompted by a thing I saw on dg28. I was trying to shoot the same subject multiple times in the same exposure with successive manual flash releases. I don't think I got I got it quite right, but you can see an example here:

August 25, 2008 5:02 PM  
Anonymous LightningPaul said...

Many thanks for this very useful info. I'll definitely try this technique.

I'll already used slow shutter flash to stop action (see my photo blog).

August 25, 2008 5:28 PM  
Blogger Paul D'Andrea said...

I've been playing with this since reading your previous posts on motion blur and flash. Three photos come to mind.

This first one is rear curtain bare SB800: Stop!

This second is also a bare SB800. We had trouble getting the timing right using rear curtain for the jump, so I took the trigger off the camera and tripped it by hand at the top of her leap. (More details in the description of the image.) Jump

This third one is technically not really Strobist, but I was working through the ideas I had gotten in the zooming with flash post. This is a three second exposure where I let the carousel burn in for the first second and then zoomed the lens. Carousel

Great stuff here, thanks David.

August 25, 2008 5:38 PM  
Anonymous hive said...

@Chris and David
Personally, the only time i'd use Second curtain sync is when I'm shooting stuff that needs a logical sense of movement; a moving bicycle would look pretty weird in first curtain.

Well, it really depends on your audience... any photographer will probably consider the technical aspect before the subject matter; others will just dismiss a picture unless it triggers an emotive reaction; flashy colours or a subject they like.

August 25, 2008 8:10 PM  
Blogger db123 said...

Great post David. I too prefer frong-curtain flash, for the same reasons.

I was trying a big of shutter dragging on a recent photoshoot, trying to mimic the shriek the "fantasy wraith" model acted out in this shot:

Definitely had to start my motion before firing the camera...definitely need some more trying...its tricky to get looking decent.

August 25, 2008 10:42 PM  
Anonymous Nathanael Gassett said...

@Paul Interesting photos! I particularly enjoyed "Jump". Nice colors, and just enough whimsy to suit the setting.

August 25, 2008 10:44 PM  
Blogger Nick Davis said...

Ye Gods, the Strobist posts not at midnight!?!? Now I'm all messed up.

Thanks as always for the post, is there gonna be an assignment to go along with it? And thanks again for the advice and tips back at the January seminar out here in sunny California, my business is really taking off and I definitely have you to thank for a big part of that.

Nick Davis
Cycle 61 Photography

August 26, 2008 12:09 AM  
Blogger ogalthorpe said...

Nice timing. I just shot a couple portraits using this technique about a week ago.

I did one with spin. And one with zoom.

I was pleased to see your comment about low batting average. Cause I was starting to second guess myself there for a bit.

Jeremy Center
A Seattle Photographer

August 26, 2008 1:42 AM  
Anonymous jussi said...

Fliping,kickin, throwing... camera around works nicely on 'drunken bar pictures.'

My friends usualy like these shots, -both, pics and those that the bar offers.- ;D

Atleast they don't look totaly wasted in these pics as the background takes the eye away from the subject :D

Rear curtain sync, shutter 1/1, and those dark party pictures get a whole new life.

August 26, 2008 6:10 AM  
Anonymous Alexander said...

The Strobist said: And that is exactly what we will be covering in the last unit of Lighting 102...


LAST? Will Lighting 103 follow? Or are we all pros now and you can't teach us any more?

Anyway, THANK YOU for this marvelous site and the work you've put into it. Apart from wifey and kids, you are responsible for the most fun thing in my life!

Best wishes to you and family!

(Hamburg, Germany)

August 26, 2008 6:28 AM  
Anonymous Jan said...

It especially adds in concert photography (only if it is a local show where you are allowed to use flash).
Some light additions
With diffused fog in the background
And one in broad daylight

But the technique is already somewhat overused.

August 26, 2008 7:28 AM  
Blogger Josh Mullenite said...

"First of all, because the flash adds a nice margin of error to a pan shot."

This, sir, is an incomplete sentence.

August 26, 2008 7:51 AM  
Anonymous Nathanael Gassett said...

Uninformed person's question: What is the curtain sync? I'm hearing about first and second curtain sync. Is that referring to whether the flash fires are the beginning of the shot, or at the end?

August 26, 2008 10:37 AM  
Blogger j.fialho said...

I like this blog. It´s very helpfull to me. That´s why i visit it.

But why all those rules in the comment box?

August 26, 2008 4:19 PM  
Blogger Milind said...

@nathaniel: Yup, that's pretty much it in a nutshell. Remember that the flash fires very quickly -- its duration is much less than the amount of time the shutter is open. So you basically have two options:

1) Fire the flash as soon as the shutter is fully open. I'm not entirely sure, but I think this is called first-curtain sync because the flash fires as soon as the first curtain of the shutter gets to the other side of the film/sensor (i.e. as soon as the shutter is fully open).

2) Fire the flash at the very end of the exposure. This is called second-curtain sync as it happens when the second curtain begins to close off the sensor.

So why use one instead of the other? Well, first-curtain sync is nice because you know exactly when the flash is going to fire -- it's good for composition. But it can be bad with long exposures because the subject will be frozen and then continue to move -- so the motion blur will appear to be in front of the subject, which looks odd. In those situations, you use second-curtain sync so that the motion will be frozen at the end of the exposure, and the blur will look natural.

August 26, 2008 5:32 PM  
Blogger David said...


Without the guidelines -- and considering roughly 250,000 regular readers -- it can quickly turn into a feces-hurling free-for-all.

The framework gives me the grounds to reject comments that would tend to degrade the quality of discussion. Most of them are basic decency and/or common sense. And all of them have arisen because of actual former comments.


August 26, 2008 5:42 PM  
Blogger j.fialho said...

Ok David. I understand ...

João Fialho

August 26, 2008 8:09 PM  
Anonymous Anonymous said...

David, is it possible to read all of Strobist sequentially? I want to be able to either read from the beginning or back to the beginning.

I may be missing something obvious...


August 26, 2008 8:56 PM  
Blogger David said...


Yes, using the monthly archives will get you a month-by-month listing. It is on the sidebar in a drop-down menu.


August 26, 2008 8:59 PM  
Anonymous Dhanny said...

My sample

August 29, 2008 2:08 PM  
Blogger Tomer said...

Dear David
I think we just made something that can relate to this's over here:
Thanks 4 your time!

August 29, 2008 7:33 PM  
Blogger fotoman91 said...

this technique is also known as "shake and bake". just thought i'd throw that out there cuz it's a cute term. :)

August 30, 2009 2:47 PM  

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