Second curtain use of camera flash - Part 2

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.