When you’re just getting into photography worrying about what flash to use might not be at the forefront of your mind. There are tons of things to learn and understand when you’re starting out and I see a lot of photographers who try to slide by without really understanding lighting and flash.
Light is the most important thing in all of photography and video as well. Light is one of the most important tools for crafting the mood of a scene. Maybe we take it for granted because the sun is always shining but without light photography would obviously be very different.
It’s interesting that in the creation story of the bible God creates the heavens and the earth, and the earth is described as without form and void. To fix this issue with the universe God then says perhaps his most famous phrase, “let there be light”.
You can think of photography the same way. Without light your photos will be without form and void.
Of course, in the real world we don’t get to snap our fingers and create light with a statement of fact like God does in the bible. Nope, unfortunately we must use our own meager means to give form to our photography using a variety of lighting devices.
To help you better understand what to look for in a flash here are some of the common features for flashes that photographers look at.
TTL stands for “Through The Lens” and refers to a metering method for the flash that the camera uses to automatically set the flash power for the scene. TTL is the equivalent of Auto mode on your camera but for flash power. TTL is useful when you have varying conditions like a room with a varying height ceiling or subjects at varying distances. The way TTL works is that the flash fires off 2 flashes in quick succession. The first flash is used by the camera to measure the light in the scene, and then the camera uses that information to adjust the power output for the second flash which is used for the actual picture.
Recycle speed refers to the amount of time the strobe has to wait between each actual flash of light. It is an important factor for a lot of people who shoot events or moments as they happen. In general, the recycle time is shorter at low power and longer at high power. The reason why the strobe must wait between each flash firing is simply to avoid overheating the strobe or to allow the batteries to charge the capacitors in the strobe for the next picture.
Not surprisingly, it is possible to set strobes on fire by overusing them in a short period of time. It’s also possible to melt or burn color gels and modifiers if they’re mounted too closely to the front of the strobe.
Recycle speeds vary from one strobe to another. A typical range for a modern lithium battery powered strobe, or even a plug in AC powered strobe, would be something like .05 seconds at lowest power, and 2 seconds at highest power.
The standard way of measuring strobe output is using a guide number. The guide number is equal to the subject to strobe distance multiplied by the f-stop. So, a strobe with a guide number of 100 would require an aperture of f/10 at 10 feet from the subject making f/10 x 10 feet = 100. From this you can gather that a higher guide number is equal to a higher power strobe .
Different things can affect the guide number like the ISO used, flash modifiers, or the type of flash head. For instance, with a strobe like the Canon 600 EX II the guide number is relative to the zoom position of the flash head. This strobe and others like it can focus the light into a beam that has the same coverage as a 200mm zoom lens. When zoomed in all the way to 200mm the strobe has a much higher guide number than when it is zoomed out to a wider coverage like 24mm.
Guide number is only a reliable measure for certain brands, some brands have their own methods for determining the guide number which make cross comparison of different brands nearly impossible.
The power of strobes is one of the mysteries of life. As far as I know there isn’t a strobe in the world that actually describes its light output. Instead we must use things like the Guide Number to determine the lighting effect on the subject. It’s not a 100% useful way of thinking about the light output for some situations.
Larger strobes usually describe their power using something called Watt Seconds. A watt second of power is just what it sounds like, it is equivalent to 1 watt of power sustained for 1 second.
The issue with this measurement is that it is based off a whole second of time, which is basically useless.
Just for example, imagine a flash that has an 800W/s power rating. Sounds really impressive right? Well, typically 800W/s strobes are really bright, but the amount of light still hasn’t been described here because we don’t know how long the strobe is actually on.
When a strobe fires, the time that the bulb receives power and thus produces light can be lower than 1/20,000 of a second. Most big strobes when run at full power will be in the 1/250th of a second range. That means that if a strobe is described as producing 800 watt seconds at full power, you need to divide 800 by the actual time the strobe is on. In this case, an 800 watt second strobe firing for 1/250th of a second gives a total power usage of 3.2 watts.
But that still doesn’t describe the actual amount of light coming out of the strobe. Due to differences in flash bulbs, circuits, modifiers, shapes, reflectivity, etc, the actual amount of light can vary even when two strobes have the same power ratings.
The only way to really know is to test each strobe yourself.
Radio Controlled Strobes
Radio control is a newer and almost entirely commonplace method of controlling and triggering strobes off-camera. It differs from older methods of wireless triggering, such as optical slave triggering, by also offering the ability to remotely set the strobes power via the triggering device.
Most of the time radio control is simply referred to as “wireless” although it is not technically the only “wireless” method of triggering a flash, it has been taken into the vocabulary as the de-facto meaning of “wireless trigger”.
The biggest issue with radio controlled wireless is reliability. Just like cellphones randomly struggle with reception, so can strobes. I was on location for a wedding reception in an old building once, and depending on where I stood in the room some strobes would fire and some strobes wouldn’t… Bummer.
Optical triggering is now a lesser known method of wirelessly triggering strobes but is still an effective method, if your strobe supports it. (Many new strobes do not.) One big advantage of optical triggering is that it is cross platform, meaning, you can trigger different brands of strobes with one master control strobe. For people with a mixed selection of strobes this might be a nice thing to know if you’re in a studio and you need one more light to add into the mix or something like that.
The downside of optical triggering is that it does not allow you to control the power levels remotely, but if you’re working in a studio this is kind of a moot point most of the time.
The upside of optical triggering is that it is essentially 100% reliable. This is because the trigger is the flash of light. If your master strobe fires, the optical slaves will pick it up and fire as well.
Freezing the action is a unique ability of flash photography. It can allow you to get an even faster effective shutter speed than your camera’s shutter is capable of. When a flash fires the actual amount of time that the flash is on is mere thousandths of a second. Just to give you an idea of what I mean, below is a list of flash durations for various power levels for the Canon 600EX II-RT.
Many larger studio strobes will have flash durations that are significantly faster than shown in this chart.
Basically, if you are set up properly in a dark room, then use the flash at 1/128 power, it will be like shooting with a shutter speed of 1/15600. This is how photographers do things like stop the motion of a hummingbird’s wings as it’s flying.
Below is an example photo shot with the shutter at 1/160th of a second and the flash at 1/128 power. This gives us a flash duration of 1/15600 of a second using my Canon 600 EX-II. You can see the water splash and droplets are completely frozen by the flash even though I used a relatively slow shutter speed.
HSS/High Speed Sync
High speed sync is an important feature for some situations where there is ambient light that needs to be controlled, such as outdoor shooting. There are also some corner cases where HSS can be used when trying to stop motion that is outside the strobes range, or where the blended light of ambient and artificial may cause some ghosting at the edges of subjects. HSS is necessary when trying to sync faster than the camera’s normal sync speed. On most DSLRs the maximum normal sync is somewhere between 160th of a second to 400th of a second. If you want to shoot flash with a shutter speed higher than that you’ll need a flash that can work in HSS mode. HSS has a big disadvantage though, it reduces the power of the strobe output. This is because when in HSS mode the strobe fires multiple times as the shutter passes over the sensor. It all happens too fast for your eye to see so it just looks like one flash. Firing multiple times in such a short period of time means the strobe needs to use a lower power output over the extended time period.
The easier, and more natural way to balance an exposure where HSS seems appropriate is to use an ND filter instead of HSS. It isn’t 100% certain to stop all motion because of the blending of ambient with the flash, but, if your goal in using HSS is simply to balance a bright sky with a fill flash on a person then using an ND does the same thing as raising your shutter speed.
Getting your first strobe
I would start cheap then work your way up in the world of strobes. If you’re not interested in that, the Canon 600EX II is a good strobe to start out with and is fit for professional use. It is durable, water resistant, and runs on basic AA batteries. Other camera companies like Sony and Nikon also have their own models.
There also lots of 3rd party options in the world of strobes, such as Godox, Yongnuo, and Westcott. I have shot with strobes from all 3 of those companies and they’re all solid choices. Yongnuo wins for the lowest price, Westcott wins for the more advanced and powerful flash, and Godox is somewhere in between. Personally, I really like the Yongnuo 650EX-RF, it’s cheap and does the job most of the time.
Once you have a strobe, something you can do for fun to help you get a feel for flash photography is to replicate the water drop shot from above.
I hope this article helped you understand how flashes work a little better. Let us know what some of your favorite use cases for flash photography are in the comments below.