One of the challenges when using strobe outdoors is obtaining wide aperture to get a shallow depth of field.
Why use strobe outside in the first place? There are a variety of reasons, although the simplest explanation is: to control the light falling on the subject. This means shifting the key from the ambient to the strobe in order to darken the background, or match the ambient (or fill in) to control shadows and provide direction to light on the face.
I chose the latter for this portrait of Kindera, taken in Siesta Key, Florida.
I positioned her with her back to the sun, a common practice. This means the sun is able to provide a separation light – hair light, rim, etc. – while also providing background exposure. It also means that her face will be in shadow. I can either expose for her face, meaning the background will go very bright (and the sky almost to white), or expose for the background, in which case her face will be underexposed. To provide both background exposure and proper facial exposure, I use strobe to balance the two.
The problem then becomes one of aperture when using strobe.
Most camera shutters are limited in the “flash sync” speed to a maximum of 1/250 second. This is a design tradeoff to support very high shutter speeds – often 1/8000 second. If you exceed this, then a portion of the shutter will appear in the frame as a black bar. The more you exceed it, the more black you see.
So, consider the “sunny 16” rule: if I am at ISO 100, then my exposure is 1/100 second at f/16 on a bright clear day. If using flash, I get a little more than 1 stop to play with (less on my camera, as its sync speed is 1/160) by using a higher shutter speed. So I max out at f/11 or so. Doable, certainly, but then the entire world is in focus. Or so it seems.
The traditional way that I handled this was to use a neutral density (ND) filter of some sort, which blocks light entering the lens. This allows me to select a wider aperture as less light is entering the lens. It works, but is difficult as all of the light is blocked, making it harder for both me and the camera to see (and focus).
A way around this is to leverage a capability of the camera – and certain strobes – to have the shutter speed be independent of the flash sync speed. They do this by either pulsing the flash (hypersync) or by having the flash pulse be timed to the entire duration of the exposure (HiSync). My camera/strobe combination again uses the latter method.
If your camera supports it – and very few small cameras do – another solution is to have the shutter in the lens, called a leaf shutter. There are still limitations, as shutter speeds go from around 1/600 to 1/1600 for one manufacturer. And the lenses are expensive, as they contain a shutter mechanism in addition to the lens optics. There are also cameras that use electronic shutters which have higher flash sync speeds (theoretically any shutter speed, though these tend to be shorter in their maximum quickness).
Using an HS head on my Elinchrom Quadra, with its flash trigger, I can shoot at f/2 in this case, giving me a very defocused background. The shutter speed here was 1/2500 second at ISO 100. It’s an amazing system, allowing me extensive creative control while keeping my equipment much simpler. Another benefit is I can stop motion using higher shutter speeds, something not possible when using a filter (as the shutter speed is still limited in my case to 1/160 second). I’m talking outdoors or any situation where there is significant ambient contribution to the exposure. You can still get an image, but there will be some ghosting. You can control that using rear curtain sync to place it behind the subject. But, why bother when you can absolutely stop motion using the HS head. In studio, it’s not a problem as the flash – and not the shutter speed – determines exposure, and I have heads with very short flash durations that can do that.
Another tool in the box.
And a portrait of a lovely lady, with focus on her.