03 - dragging the shutter
flash photography techniques
flash & ambient light 
dragging the shutter 
bouncing flash
Here I want to touch a bit more on mixing flash with the available light, so that the mood of the setting is retained, or at least so the available light still adds to the image.
It is crucial to understand that within a certain range, shutter speed has no effect on flash exposure. This key will allow us to better mix flash with available light - by controlling the shutter speed.
[update: Feb 29, 2008]
After reading this page, also please go through the following page where this technique is discussed as well: “Dragging the shutter” revisited.
With TTL flash, the camera & flash will follow our chosen aperture and iso combination - but this will also affect metering (and exposure) for available light. So this conveniently leaves us the shutter speed to control the available light. It’s very important to grasp this.
By bringing the shutter speed low enough that available light registers on the image, you can retain most of the mood of a setting by not over-powering it with flash.
This is called dragging the shutter.
Have a look at these two photos. Not particularly wonderful, but they clearly illustrate a point.
Both were taken seconds apart with two D100 cameras, each with exactly the same custom tone curve. Aside from resizing for the webpage, there was NO manipulation in Photoshop .. these images are straight out of the camera. And yet they look completely different.
1/15th @ F4.5 (400iso) |
1/60th @ F5.6 (400iso) |
I photographed the image on the left, and a photographer working with me as a second-shooter, took the image on the right. As you can see from the skin tones and the white of the shirt, the basic exposure for the groom is accurate enough for both photos. This difference is due to our camera settings. I used a much slower shutter speed, and a slightly wider f-stop. With this, I allowed nearly 3 stops MORE ambient light in. And it shows. The image on the left just looks so much better .. same opportunity, same setting, same subject .. but very different results.
The essential difference is that I chose my settings.
I only shoot in manual mode, hence *I* decide on the results I want to get. And I got it.
By shooting in Program Mode, the other photographer allowed the camera to make the decision - and the camera set a shutter speed that is too high. I wanted ambient light to register, and I set the
f-stop and shutter speed to where I could see from my camera’s built-in meter that I would get ambient light to register.
Even though the type of flash lighting used in these shots were quite different, the resultant look is nearly entirely dependent on the fact that I took the ambient light into consideration (via my camera’s meter) and purposely set my shutter speed accordingly. btw, I used a Quantum Q-flash bounced into an umbrella behind me, and the other photographer used a Speedlight on-camera.
This technique of using a slower shutter speed to allow ambient light to register, is usually called “dragging the shutter.” With this, you’d use your camera’s light meter like you normally would ..
.. but instead of using it to expose perfectly for just the ambient light, now you use it as a guideline as to how much ambient light you would like to register. And somewhere around 1.5 to 2 stops under-exposure will still give you enough detail in the background - and then you use flash as your main light source, and use the light from your flash to expose correctly for your subject.
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Another example:
Once again, the two images look quite different. Going by the skin tones, the overall exposure is correct for both images. The difference comes in with how the ambient light was allowed to register in the second image.
settings for 1st image: 1/50th @ f5 @ 500 iso
settings for 2nd image: 1/20th @ f4 @ 500 iso
I want to stress here, that these images where not manipulated in Photoshop, but were only adjusted for white balance in Adobe Camera Raw. So this is the kind of result you can see directly out of your camera already, when your settings are chosen with some thought.
By dropping my shutter speed and opening up my aperture a bit, I allowed a lot more available light in. It did help that he was standing in a area which is a little bit darker than the background area. This meant I could get away with a slow shutter speed, without noticable camera shake.
( In both images I bounced the flash up and over my shoulder.)
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Specific settings:
I’ve seen some photographers give advice like “shoot at 1/8th sec @ f5.6″ .. but that kind of advice about exact settings is misleading, since every situation is different.
The actual shutter speed chosen will depend on circumstance and the effect that you want,
- and the amount of ambient light that is available,
- and whether you have a tripod,
- or can shoot with a steady hand at slow shutter speeds,
- and the f-stop chosen,
- and whether you can bump up the ISO to allow more ambient light in,
- and how much subject movement there will be, or you will find acceptable.
There are a number of interlinked factors here that you balance out depending on the scenario. But in the end, the photograph where the flash and ambient light is balanced by using an appropriate shutter speed, just looks so much better in comparison to a photo where the flash light completely dominates.
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Adding motion:
Here’s an example where I dragged the shutter not only to get more available light,
but purposely zoomed my lens during exposure, to add a sense of motion:
Specific settings: Nikon D2H; Nikon 17-35mm f2.8
1/15th @ f4 @ 800 iso / manual; matrix metering / TTL flash: -1 exp comp
The shutter speed and aperture and iso was specifically chosen so that the street scene would record in this image. I was fortunate that the couple was in a darker area, and therefore mostly lit only by flash. As I tripped the shutter, I also zoomed, thereby getting these streaks of light converging on the couple.
Because they didn’t fill the entire frame, I couldn’t rely on the TTL metering of the flash to give me correct exposure, so I dialed down my flash exposure compensation.
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1. When you add flash to ambient light, don’t you over-expose the subject?
Speaking very broadly, there are two main scenarios (with any possible combination inbetween):
In the first scenario, the background is brighter than the subject, and you set your exposure to give near correct exposure for the background. Since your subject is darker than the background, they’d still be under-exposed. Then you use your flash to expose correctly for them. This is the simplest scenario.
But usually what you’d encounter is low light situations where the background and your subject have about the same kind of light on them, and would need the same exposure. So what you’d do here, is intentionally under-expose for the ambient light - around 1.5 to 2 stops - so that the ambient light registers, but doesn’t dominate. Since your subject would then still be under-exposed, you would then use your flash to expose correctly for your subject.
So by adding flash, you wouldn’t over-expose your subject, since you are pulling down your ambient exposure. You will encounter a lot of different lighting situations, but those two scenarios cover the basics.
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2. How do you deal with slow shutter speeds?
I often get asked why the images displayed here that were taken at slow shutter speeds, still appear sharp.
The reason why you don’t see (much) camera shake in those images, is that I do take care in keeping my camera steady, but there’s more at work here than just the basic technique.
The image of the piano player (and another image on a subsequent page) probably have a measure of camera shake - BUT - it is in areas which aren’t important - the background, the city lights. They are slightly out of focus anyway because of minimal depth of field.
The couple walking against the city lights, were in ’shadow’ and the piano player was in ’shadow’ . Without flash they would’ve come out sillhouetted / black. The roll-over image of the piano player shows this clearly.
The flash therefore freezes any camera shake, since the available light falling on my subject(s) is so low. You just wouldn’t see camera shake. Since the flash is pretty much an instantaneous burst of light, it will freeze action / camera shake.
Therefore you simply don’t see camera shake .. even though it probably does exist to some extent in the background.
[update: Feb 29, 2008]
Also read through this webpage, where this is discussed in more detail.
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Please feel free to e-mail me with comments & questions.
Neil van NiekerkIf you feel you need more direct help or instruction with this and other aspects of digital photography, I do present workshops and seminars.
I also offer individual tutoring sessions.If you feel that you have benefited from these webpages, then a small donation via PayPal would be welcome towards the cost of hosting these webpages. Thank you.