Speedlites, also known as hot-shoe flashes, are battery powered flashguns that can affix to the camera via hotshoe. Modern speedlites have a rotating head to aim the flash, can have their output controlled, an automatic function and can be triggered off camera.
There are many advantages to speedlites over a traditional studio flash head. The first, and perhaps most obvious, is their portability and accessibility being, able to fit in almost any camera bag and being battery powered mean they are very easy to carry around and power.
This makes lighting very accessible on location shoots such as wedding and out-of-studio portraits.
A problem that can occur with on-camera flash is that is can produce very hard, intense and flat lighting making most images lack depth and unflattering. Such as the image below, shot with speedlite on camera, facing forward and in TTL mode.
You can see the result is a very hard and flat lighting, this is due to the flash head being a small light source and that is is firing almost directly from the lens' point of view. You can see the hard outline of the person's shadow behind her and on her clothes.
The background is supposed to be black but due to the direct hard light on it appears a dark grey in which you can see the folds and creases.
The light however is well exposed due to the TTL function of the speedlight. As metering light on the go, particularly in event photography, is unrealistic I use TTL which stands for Through The Lens.
TTL is essentially auto mode in which the speedlight will quickly fire a preliminary flash and meter than flash through the lens before setting the correct output to correctly expose the image. This happens incredibly quickly and is unnoticeable but serves as a really useful function.
In this image, the flash head is pointing up to the ceiling. This turns a very small light source is a very large one as the ceiling turns into a giant reflector.
The result is soft, even lighting that looks very natural due to the top down direction and white ceiling reflecting daylight colour light back onto the scene.
I wanted to try a freeze motion with flash however, typical studio lights have are limited by the camera maximum sync speed meaning sync speed higher than around 1/200 are not possible.
This is because SLRs tend to have a focal plane shutter, which takes around 1/200sec to travel the height of the camera's sensor. As flashes are instantaneous by comparison, you can catch a shadow of the focal plane shutter as it travels like you can in this image shot at 1/250. Though interesting, my camera's top flash sync speed is 1/250 with it's pop-up flash.
However, in freezing motion you typically want shutter speeds of around 1/500 upwards, which is a problem with flash photography and focal plane shutter cameras.
HSS
Speedlites (and more modern studio lights) have a function called HSS (High Speed Sync).
With this function you have shoot at higher speed as the flash, as opposed to firing a single burst of light, will fire several in stroboscopic fashion extremely quickly meaning the shadows of the shutter are exposed allowing you to shoot at higher speeds.
The pay off for this however is typically a weaker output in intensity as the speedlite cannot charge it's capacitor quick enough to let off full power bursts.
I did the following shoot at home and put a emphasis on freezing motion as opposed to creating a usable commercial image. As such composition and styling took a back seat and I simply focused on freezing the motion and positioning the light in a pleasing way that would highlight the glass and splash well.
I starting with my camera on a tripod as I need a free hand for the splash, and attached a HSS compatible remote trigger on the hotshoe and set up a light stand with a radio receiver and speedlite attached. This allows me greater control of direction of light as I am not bound by simply reflecting the light.
With the flash in TTL mode, I set my shutter speed to over 1/250th and took several test shots.
As speedlights lacka modelling light I had to take several shots like the ones below to see how the light would look and varying aperture to see what level depth of field would create a better image.
With TTL I can make these changes and not have to worry about exposure changing, though exposure isn't consistent throughout possible due to the reflectivity of the glass/metal.
Once I settled on the lighting, I set my shutter speed to 1/1600 to freeze the motion.
