Simply put, the slave mode on your flash will allow you to fire that particular flash when it senses the flash from another speedlight.
There are a few different situations in which you might find yourself needing to enable slave mode on your flash. The most common situation is when you don't have enough flash receivers to trigger all of the flashes you are trying to use at the same time.
TIP: If you plan on using your pop-up flash to trigger your speedlight in slave mode, you will have to compensate for the extra light coming from your camera. Use flash exposure compensation to turn down the flash power on your camera and help reduce the effect of that extra light.
The concept of slave mode is quite simple. The setup is very easy and quick to do; all you need to make sure of is that there is a clear line of sight to another flash.
To get your speedlight into slave mode, all you have to do is toggle the “Mode” button on the back of the flash. Most flashes will function in a similar way.
You can use slave mode to work with any brand of speedlight. All the speedlight is doing is detecting a pop of light to trigger itself. Some photographers will have their nice speedlight as their key light, but use more affordable flashes as fill light and easily trigger them with slave mode. You can also trigger a flash in slave mode by using the pop-up flash found on your camera.
The way to make the most out of the gear you have is to set the rest of your flashes without receivers to slave mode. BEWARE: Because slave mode is dependent upon the flash of another speedlight, you will need to make sure that there is a clear line of sight to the other flash.
For example, the photo shoot with this car had a set of lights on the outside of the car, as well as a speedlight on the inside of the car. With the limitations of slave mode, the flash inside the car could not be set to slave mode simply because it did not have a direct line of sight to another flash. However, the flashes on the outside of the car were set to slave mode because they did have direct line of sight to another flash. It is safe to assume that the more creative your light placement in your setup, the less likely you will be able to use the slave mode on your flash. For most situations you should be just fine.
If you are looking for a set of triggers/receivers for your speedlight, we recommend the Yongnuo Radio Transceivers (Canon – Nikon – Sony). Here at Improve Photography, we have taken these transceivers and have put them through the paces. Because these rely on radio frequencies, you are able to use your off-camera flash at a greater distance than would otherwise be possible with infrared. An additional benefit to radio triggers is better response between the camera and flash.
For other flash photography gear, visit our Recommended Gear Page.
The latest YN-560 III comes with a built-in receiver. This means all you need on your camera is the trigger to fire the flash. This takes away a lot of the frustrations of working with other variables of flash photography. Not to mention those extra batteries for everything that go into the entire production!