Off-Camera Flash Jargon Explained

Off-Camera Flash Jargon Explained
Don’t be overly concerned with complex sounding words such as ‘rear-curtain synch’. All of that will soon become clear.

Here is some off-camera flash jargon to get you started:

Off-Camera Flash

Off-camera flash is simply a flash unit that is not permanently fixed to your camera. When photographers speak of ‘off-camera flash’ they are usually talking about the small flash units as oppose to the larger more professional flash units in studios. Those are normally referred to just as flash, studio flash or monolight (a monolight is a flash unit with its own independent power source built in).


TTL means ‘Through the lens’. Canon calls theirs E-TTL which stands for ‘evaluative though the lens’ and Nikon i-TTL for ‘intelligent through the lens’. This means that if your flash unit is TTL enabled it will use the camera’s metering system to try to gauge how much flash is needed for the subject. TTL is like using metering on your camera but for your flash. Sometimes it is great and other times it is way off the mark.

Manual Mode

Manual mode means that you switch off the TTL capability and choose to use a mode that allows you to choose the flash output manually.

Flash Synch

Flash Synch means flash synchronisation and this means that the flash is synchronised with the opening of the shutter when you take a photo. The two need to be in synch with each other.

Flash Synch Speed

Flash-Synch speed refers to the maximum shutter speed of the camera that you can use, in order for the whole picture to catch the flash from the flash bulb. On modern cameras, the flash synch speed is around 1/200 of a second or 1/250 of a second (it’s best to read the manual for the exact speed for your model of camera). If you use a higher shutter speed than this, you will find that you get a black section across your photos. This is caused by the fact that the shutter curtains were already closing, whilst the flash was firing, and only part of your image was being exposed to the flash. Using the correct flash synch speed for your camera, ensures that the shutter curtains are fully open when the flash fires.

Slow-Synch flash

There is nothing stopping you from using a slower speed than the flash synch speed. This is referred to as slow-synch flash. When you use a slower shutter speed you allow the flash to fire and also let in the ambient light after the flash has fired, so you tend to get a more natural result.

Rear-Curtain Synch

Rear-Curtain Synch is when your flash fires just before the closing of the shutter. The default mode for flash is front-curtain’ mode . It is called this, as the flash fires just after the shutter opens. Rear curtain synch is used often in photography where there is movement. Imagine that you wanted to take an image of a car at night passing from left to right across the camera frame and have the lights of the car trailing the car in the image. If you decided to use the default front-curtain mode of the flash, along with a slower shutter speed, (slower than the max flash synch speed), you would find the trails would be in front of the car on the photo. This is because the flash at the beginning of the shot freezes the car and the slower shutter speed, records the lights of the trails. Because the car lights are recorded after the flash the lights end up looking as if they are in front of the car. In this instance, you would want the lights of the car to be recorded first and then the flash to expose the car to the right of the frame and therefore you would choose rear-curtain synch. This can be confusing, so the best thing to do is practice and you will understand better when you see everything visually.

Flash metering

Flash metering is what your flash does if it is in TTL mode. The flash fires and does a calculation of how much light it should output for that subject to be exposed correctly.

AF Illuminator

AF illuminator stands for Auto Focus illuminator. It is a red patterned light, which is emitted by the flash (in dark conditions) to allow your camera to see the subject and focus the lens correctly.

Flash exposure compensation

Flash exposure compensation is similar to the exposure compensation on your camera but it is for the flash. Just as you can decide to add or take away light by changing ISO, aperture or shutter speed, you can also add or take away light from the flash. If you are in TTL mode and you think the flash output is not right you can use the plus and minus buttons to change the brightness of the flash.
Now that some of the jargon has been explained, I hope that if you have an off-camera flash and a compatible camera that you will throw caution to the wind and explore the creative options that flash can bring to your photography.

Enjoy your creativity!

You Should Also Read:
Off-Camera Flash Photography Mistakes

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