In part 1 of this article I discussed the use of second curtain flash in action photography especially when you want to include a trail of your moving subject. Sometimes, however, you may not be able to use second curtain flash when or how you would like to.  In some cameras, that function is only available in certain shooting modes such as manual mode, or if you can use second curtain flash in automatic mode you may be restricted to a shutter speed of 1/60 of a second..  One sixtieth of a second maybe too fast to record the ambient light you want to capture. Check your camera’s owner’s manual to find out which shooting modes allow the use of second curtain flash sync and what other limitations may apply.

Another consideration for using second-curtain sync is the type of background you’re using and its tone in comparison to the moving subject.  Your background should be as simple as possible.  Avoid backgrounds that will compete with the trail. If that is not possible there are a couple of options that you can experiment with. You can darken the background rendering it less noticeable by using a faster shutter speed as long as it’s not faster than the sync speed (See part 1 for discussion of sync speed). If that negatively impacts the capture of the trail you may have better luck increasing the distance between the camera and the subject.  This takes advantage of the inverse square law.

The effect of inverse square law in photography is easier to see if you point the flash directly at an object.  When you move the camera away from that object the effect of the flash is reduced by the inverse square of the change in distance.  For example, if you placed a camera 3 feet from your subject then moved it to five feet the effective strength of the light would be 1/4 what it was before.  Had you moved the camera from 3 feet to 6 feet, then the effect of the light would be 1/9th.

For an interesting example of using second-curtain synchronization as a technique in action photography see this site.

Second curtain use of camera flash – Part 1

By Katriel


Knowing the difference between first and second curtain use of a flash in photography increases the options a photographer has when shooting action. Let’s take as an example a runner jogging at night.  If the goal is to show the path of the jogger as s/he passed across the camera’s field of view you could just simply use a slow shutter speed, however, you would lose a lot of detail in the subject. By firing your flash on its default setting (assuming you’ve never made changes to the flash) with a slow shutter speed you could freeze the subject and still capture the ghostly trail. But what if you want the trail to appear on the opposite side? This is where second curtain sync comes in.

So what is second-curtain sync or first -urtain sync?

Digital SLR cameras use plane focal shutters to help control the length of time light strikes a sensor. For the most part the shutter consists of 2 sets of metal or cloth blades. These sets of blades create a blind between the sensor and the light coming through the lens’ aperture except for a slit of space between the blinds when they travel across the sensor.  Each blind is called a curtain.



When you press the shutter release button one of the curtains moves across the sensor exposing the sensor to light.  There will come a point in time when the entire sensor is exposed to light before the 2nd curtain begins its travel if the photographer is  using a shutter speed less than or equal to 1/60 of a second. (Many higher end cameras today can use what’s called –high sync speeds of 1/125 of second or faster .) 

A flash’s sync speed (or synchronization speed) is the fastest shutter speed a photographer can set which will leave the entire sensor completely open to light for a brief period. A flash needs to fire during the time the entire sensor is exposed to light; otherwise, you will see an image of the second curtain as it travels across the sensor.  That part of your photograph will appear black.  If you still use a film camera it will look like you did not advance the negative completely and as result only recorded part of the scene.

The time lapse of a flash is much faster than the sync speed.  Depending on the hardware a flash’s burst can be anywhere from 1/500 of second to over 1/4000 of second which is fast enough to freeze most moving subjects.  In the world of photography then that leaves plenty of time for ambient light to also be recorded onto the sensor.  When you use 1st curtain flash, ambient light is recorded after the flash burst.  When you use 2nd curtain flash, the burst of light the flash fires occurs right before the 2nd curtain begins to move; obscuring light from the sensor. The ambient light is recorded prior to the burst of light.  With slow shutter speeds moving subjects will be recorded blurry except at the point of the flash burst.  This can lead to lead to some very interesting effects when shooting action such as having your shadow chase you or you chase your shadow (assuming you’re the subject of the picture).

So what else do you need to know before taking shots using 2nd curtain synchronization? Plenty. Such as why using high-sync speeds may cause problems if trying to capture a motion trail. Also the shooting mode to which you’ve set your camera may prevent you from using 2nd curtain sync.   Another consideration is the tone of your subject in comparison to the background and how much of the background or ambient light you actually want to record. You may want to record less ambient light than the shutter speed you set will produce. Knowing the inverse square law is helpful when you want to minimize ambient light.  Part 2 will cover these issues.