The scene: Outdoors with full sunlight.
The gear: Your camera, lens, and flash.
The problem: You find that your flash only works at 1/200s or below, so you need to be at f/16 or f/22 to get a well-exposed shot. And at f/16-f/22, everything is in focus, including all the cars and other distractions in the background. (Those dust spots you keep meaning to clean are also perfectly visible.)
Why can’t you shoot with a higher shutter speed so you can have a wider aperture?
Well, it’s all down to the issue of sync speed.
More specifically, it’s about using flash and high-speed sync.
Generally speaking, to overpower the sun and stay below your camera’s sync speed, you’re forced to use a narrow aperture. Here I’m at f/20 just to stop the backlight overpowering the hair and the sky from blowing out:
The resulting aperture means that everything is pretty much in focus, leaving the background looking cluttered.
(This shot is for example only; you should generally make a point of choosing clutter-free backgrounds.)
What is sync speed?
Sync speed is the fastest shutter speed for which the camera can expose the whole frame at once.
It’s a bit technical, but when you fire any shot below the sync speed, the first shutter curtain opens fully, revealing the entire sensor to light. At the end of the exposure time, the second shutter curtain moves across the frame to finish the capture.
(Generally, the sync speed varies between 1/125s and 1/250s; it depends on your camera.)
When you go above the sync speed, the second curtain starts to move before the first one has completed its journey. As your shutter speed gets shorter and shorter, the gap between the curtains narrows to a tiny slit. Despite this, all parts of the sensor receive light and a full exposure is made. On a bright day with a prime lens, you can easily shoot at 1/8000s at f/1.4 and have a perfect exposure. All parts of the frame still receive light, because ambient (non-flash) lighting is continuous throughout the exposure.
So why does the sync speed actually matter?
The sync speed problem
It’s when you introduce flash that you start to have problems.
You see, when a flash is fired (which usually happens when the first curtain is opened), all the light from it comes out in a very short space of time (in the order of milliseconds).
When you go above the sync speed, the position of the curtains doesn’t reveal the entire frame at the time the flash fires. So the shutter curtain blocks part of the flash and prevents it from reaching the sensor.
Any ambient light will expose normally, but the flash gets hidden in part of the frame. As your shutter speed gets faster and faster, more and more of the flash is blocked until it’s no longer visible in the shot (i.e., your exposure is what you’d get if you never fired the flash at all).
Below is a set of images taken at 1/3-stop increments with a flash. The first photo is at 1/250s, the native sync speed of my Fujifilm X-T2 camera. The other shutter speeds are, in order from left to right (and top to bottom): 1/320s, 1/400s, 1/500s, 1/630s, 1/800s, 1/1000s, and 1/1250s. Note that 1/320s is potentially usable if the subject is away from the edge of the frame.
Everything in focus
Normally, when you use flash outside in daylight, you end up having everything in focus.
Remember the Sunny 16 Rule? If your subject is in direct sunlight during the day, you can set your aperture to f/16 and your shutter speed will be one over your ISO value.
So if your ISO is set to 100, your shutter speed would be 1/100s (at f/16). If your ISO is 200, then the shutter speed would be 1/200s.
Now, to get a darker, richer sky while using flash, you’d really need to be at f/22. Because you can’t get faster than 1/250s (remember, it’s the sync speed!), you have to increase the aperture to expose the shot correctly.
As you can see from the photos above, this is a huge problem. Shooting at an f/22 aperture just doesn’t give you the creamy bokeh that portrait photographers love, and it can leave you with unpleasant, distracting backgrounds.
So what do you do?
The solution: high-speed sync
There is a solution: high-speed sync, also known as focal-plane sync.
No, it’s not perfect, but it does work. You see, instead of firing the flash at the start of the shot, high-speed sync pulses the flash throughout the whole exposure, trying to simulate the effects of a continuous light.
It looks good, but it comes at the expense of power and heat, because HSS works the flash really hard. After a few shots, the flash may even shut down for cooling.
Now, for high-speed sync to work, you need the camera to transmit a signal to the flash and for the flash to have high-speed sync built in. Cactus Image makes a trigger called the V6 II, which allows you to use any HSS flash with any camera.
The look of high-speed sync
You can use high-speed sync to go over the sync-speed barrier, so settings like 1/4000s at f/1.4 are achievable with flash. You get complete control over the light, but while using the wide apertures you usually associate with natural-light photographs. Yes, please!
By shooting wide-angle photos with a shallow depth of field, you can even create images that look like stills from a movie.
Settings for high-speed sync
Let’s look at a typical setup and settings for a photo using high-speed sync. This particular shoot was done in the evening when the light was relatively low, but I really wanted a shallow depth of field – and therefore required high-speed sync.
I set my camera to f/1.4 for a super-shallow depth of field. To get the clouds properly exposed, I had to boost the shutter speed to 1/4000s. To get the flash to work, I had to set it to high-speed sync. Using a Cactus V6 II trigger, I could easily get my Fujifilm X-T10 to shoot with high-speed sync.
Another high-speed sync portrait example:
Note that high-speed sync isn’t the only way to shoot with a wide aperture and flash.
For one, you can always head out at the beginning or the end of the day when the light is pretty low; then the ambient lighting won’t add much to the shot, and you’ll be able to get a nice exposure at 1/200s. Plus, you can get great sky color and you won’t be fighting against strong sunlight.
Of course, if you’re doing any photoshoots with clients, you often have to work with the subject’s schedule rather than your own. So you may have to shoot at midday to suit them.
And that leads to the next option.
Using a neutral density filter
If you shoot landscape photography, you will be familiar with neutral density (ND) filters. This filter type allows you to slow the shutter speed down to get nice, silky water.
Neutral means that it adds no color, while density refers to blocking light. You can get ND filters in a range of values from 1 stop to 16 stops.
For portraits, neutral density filters allow you to widen the aperture instead of dropping the shutter speed. So a 4-stop ND filter would take you from f/16 to f/4.
The drawback is that, as you block light, focusing can become harder.
Another potential issue is that not all ND filters are actually neutral. Some tend to have a color cast. (I have a Firecrest 10-stop ND for landscapes, which is neutral, but the older 4-stop filter I own – also from Firecrest – is slightly pink.)
Flash and high-speed sync: conclusion
As you now know, you can make outdoor portraits even when the sun is bright – simply by using flash and high-speed sync.
So make sure you get a flash that has HSS capabilities.
And start practicing!
Now over to you:
Have you ever used high-speed sync? Have you ever struggled to get nice bokeh in bright sunlight? Share your thoughts (and high-speed sync images!) in the comments below.