If you’re a portrait or wedding photographer, you’re going to want to learn this professional flash trick. It’s part light speed control and part shutter speed magic, and it requires a good understanding of how your camera creates an image when using the flash.
It’s a great way to introduce stunning and attractive light gradation into your images, all without the aid of software. The good news: all you need is a single off-camera flash – no need to buy fancy light modifiers or studio strobes!
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When your camera’s shutter is released, it moves up and away from the sensor, exposing the chip to light and allowing a digital image to be created. As you might expect, the higher the shutter speed value, the faster this cycle ends; and the lower the number, the longer the sensor is exposed. Although your camera has a range of shutter speeds, from around 30 seconds to perhaps 1/8000s, you will often find that you cannot use all of these speeds when using flash.
The maximum sync speed is usually 1/200s, although on some cameras it may be 1/250s or even 1/320s. If you try to use a shutter speed faster than this, one of two things will happen. On some models, the shutter simply will not fire if the flash is on, or the flash will simply not fire. In other cases, when the maximum sync speed is exceeded, a black line appears along one edge of the frame, creating uneven exposure.
The higher the shutter speed, the darker the frame and the darker the gradient. This is because the shutter physically manifests itself in the shot, as the flash is only “active” for part of the total exposure. In other words, your camera cannot guarantee that the shutter is fully open when the flash fires, so it is partially closed when this burst occurs. This means that the flash light is not captured across the entire frame, creating unevenness.
In most cases, this is seen as a bad thing – an undesirable phenomenon to be circumvented by keeping shutter speed below maximum sync. However, there are creative applications. By carefully balancing the flash with the ambient light, so that the differential is not too pronounced, it is possible to introduce an attractive dimming effect. This technique, often called “cheating the timing” and popular with wedding photographers and environmental portraitists, adds weight to the bottom of the frame and helps focus attention on the subject’s face.
There are two things to know first. First, it’s essential to switch to manual exposure and flash modes to prevent the camera from defaulting to the maximum sync value. Second, although this is unlikely to be a problem with a recent camera, it is worth checking the direction the shutter moves in your model. If it’s a horizontal plane shutter, found in some older cameras, it won’t work: the gradient will be in the wrong part of the frame.
1. Configure the wireless system
Although your camera and flash can communicate wirelessly, sometimes it is necessary to use a third-party trigger to allow the flash’s maximum sync speed to be exceeded. You can also use a compatible third-party flash. Opt for radio triggers for maximum reliability.
2. Adjust light output
Calculate the ideal balance between ambient and artificial light for the perfect exposure. Turn off the flash if it’s too bright and reflecting off your subject. A setting of ⅛ power is a reliable starting point and increases or decreases as needed.
3. Select exposure
Choose an f-stop that allows you to increase shutter speed above maximum flash sync – usually around 1/200s. Start with f/8 and adjust as needed, stopping if your speed gets too high. Increase the ISO instead if you need shallow depth of field.
4. Increase shutter speed
You can do this in manual mode, but switching to shutter priority mode will allow you to focus on exposure time, while the camera controls aperture. If the maximum sync speed on your camera is 1/200s, try using 1/250s or 1/320s to start with.
5. Give it a try
Take a picture and notice the darkening effect at the bottom of the frame, caused by the flash not lighting the whole picture evenly. The aim should be to introduce a subtle effect, so adjust exposure and flash output accordingly.
6. Push to the limit
If the irregular lighting is not clearly visible, try increasing the shutter speed to find the maximum possible setting before the transition from light to dark becomes too sudden. Adjust the position and height of the light to vary the effect.
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