How to Choose a Flash? 10 Factors to Consider When Buying an External Flash

Below are the 10 features you need to look out for before buying an external flash unit. Hopefully, by the end of this article, you will have a basic idea of the features you need.

Lighting is an essential aspect of photography—it can either make or break an image. When you use the built-in flash of a camera it introduces harsh shadows and unnatural brightness to the shot.

Fortunately, external flashes are made to give just the right amount of light. Also known as a speedlight, an external flash offers more control over the lighting to help you achieve natural-looking results.

But with so many flash units on the market, choosing the right external flash can be overwhelming.

In this article, you will learn how to choose a flash by understanding ten key features. I will discuss each feature in-depth to help you understand its importance in photography lighting.

Brand of the Camera Flash

In the past, if you wanted to buy a flash, you needed to get one from your camera manufacturer—usually Canon or Nikon.

Today, you are no longer limited to these manufacturers. You can now choose a camera flash from various companies, such as Godox, Nissin, and Yongnuo.

In general, these third-party flashguns are cheaper compared to the big names in the industry. Some models also bring serious competition to the top brands in terms of power, durability, and overall performance. So make sure to look into these options when shopping for the best external flash.

With that said, flashes from your camera manufacturer are still worth considering. They might be more compatible with your camera. That means you can take better advantage of all their functions.

Flash Power

One of the first considerations when choosing a camera flash is its power output, which is expressed through a guide number (GN).

I don’t want to get too technical about the GN, as it’s pretty overwhelming for beginners. 

However, the most important thing you must know is that a higher GN value results in a more powerful light. It also affects the cost of a flash unit—a greater GN is equivalent to a pricier product.

For instance, Canon has a flash line-up consisting of 270EX, 320EX, 430EX, and 600EX. The figures in these speedlights are related to the guide number—270 has a GN of 27 meters, 320 is 32 meters, and so on. However, these guide numbers vary based on the aperture (F-stop), the focal length of the lens, and your distance from the subject.

Below is the simple formula for calculating flash guide numbers:

Guide Number = [F-Stop] x [Flash to Subject Distance]

Always remember to measure the distance you are likely going to cover with the camera flash. 

You can always reduce the flash power if you feel the light is too harsh. However, you cannot increase the flash output beyond what it can offer.

So it’s essential to buy a camera flash that can reach and illuminate your targeted subject in the first place.

Automatic (TTL) or Manual Control

Flashguns offer two flash modes, namely TTL and fully manual. Some flashes only have a single flash mode, while others include both.

TTL stands for Through The Lens. It is an automatic flash that takes an ambient meter reading of the scene and fires a low-power pre-flash. After that, it compares both readings and determines the optimal amount of light required to illuminate a scene.

Since the flash automatically computes the light needed, TTL is far more accurate and reliable in flash photography than manual mode.

Despite being an automatic flash, TTL still offers flexibility through flash-exposure compensation. This function enables you to adjust the flash power for greater control over the lighting.

For these reasons, the TTL flash mode is suitable for capturing most types of subjects and sceneries. But it especially comes in handy in situations where distances and lighting can easily change.

In contrast, a manual flash exposure relies on you to set the flash power output. Thus, it requires extensive knowledge and experience with flash photography. Beginners may find it harder to use than TTL flash units.

On a more positive note, it gives you far greater control over the illumination of a subject. Most manual flashes are also cheaper due to their simpler construction.

So if you want to achieve a particular look or mood or save money, a manual flash is the way to go.

Autofocus Assist Beam

When shooting in low-light situations, the camera and lens might find it hard to focus on the subject. Fortunately, a feature called autofocus assist beam is available in many external flashes.

As its name suggests, it can assist the camera lens in focusing on a subject by lighting up the scene momentarily. This short burst of light can help the lens see the object in low-light and, thus, focus on it.

Another advantage of this function is its ability to fire just “enough” light towards the scene. It does not produce highly invasive flash beams that blind your subjects, unlike the camera’s built-in flash.

However, note that most AF assist beams only work at short distances—around 15 to 20 feet—due to the low-powered light.

It’s also best to use a camera with several autofocus points if you want to take full advantage of this feature. That is because the flash can only produce light for a short period. So if you use a camera with a slow AF system, it will defeat the purpose of having this functionality in the first place.

Flash Recycle Time

When the flash fires, it “cools down” for a short period before it is ready to shoot again. The flash recycle time, also known as recycle speed, determines how quickly you can resume firing the speedlight.

The recycle time is expressed in seconds. Most manufacturers mention two different periods, such as 0.3-5 seconds.

The smaller number indicates how soon you can fire the flash again at its lowest light output or power setting. Meanwhile, the larger figure denotes how quickly you can take another flash shot at its maximum light output or full power.

The more important recycling time to consider is the larger one. If possible, choose a flash that offers a short maximum light output time. It enables you to use the speedlight continuously while capturing a series of photos in burst mode.

However, the flash recycling speed is only crucial for action and sports photographers, who often use burst shooting mode. If you take portraits, then this feature isn’t quite as essential when choosing a flash.

Swivel and Tilt Flash Head

The pop up flash of your camera can only point in one direction, which limits you significantly. 

Fortunately, most external flash units have the advantage of being able to tilt and swivel at your desired location. This function makes it easier to bounce the light off a wall, ceiling, or any white surface. The result is softer and more even lighting that complements the subject.

However, before buying a wireless flash, make sure to check its tilt and swivel range in the description. It will list how far the flash head can angle up or down and rotate in degrees.

It’s best to choose a flash that enables you to bounce the light emitted at almost any angle you want. It gives you more flexibility.

Auto-zoom Setting

Similar to camera lenses, external flashes also have a zoom setting. 

This function can automatically adjust the flash output based on the focal length of the lens. When using a wide-angle one, the flash can spread light towards the sides to illuminate more of the scene. But on a telephoto setting, the speedlight can redirect the beam on a narrower pattern.

By ensuring that the light beam covers the view angle of your lens, the auto-zoom offers two significant benefits. First, it can illuminate the scene evenly. Second, there is no wasted light, meaning you can expect the flash to brighten more of the subject than what you can see through the viewfinder.

Wireless Capability

Taking the flash off the camera is one of the best ways to expand its capability. So you might also want to consider buying a flash with built-in wireless capability.

It allows you to control the flash settings remotely. It also enables you to use multiple flashes within a scene to achieve various effects.

However, make sure to check if the wireless functionality is compatible with your camera. Some older models require you to add an accessory to the flash in order to control its settings.

For those who want to use an off-camera flash but don’t have built-in wireless, you can pair the flash with wireless adapters. Do note that these products come at an additional expense.

High-Speed Sync

Most external flashes offer a few synchronization modes, such as front curtain, rear curtain, and slow sync. However, only a few speedlight units feature high-speed sync (HSS).

To understand why this feature might be important to you, I’ll briefly discuss flash sync. 

In simple terms, flash sync speed refers to the action of matching the speed of the flash with the shutter speed setting in your camera. 

Most cameras offer native sync of 1/250th of a second. If you shoot anything faster than this (for instance, 1/400th), it can affect the flashgun’s ability to sync with the camera’s shutter speed. It also leads to overexposure, and in some cases, black bars in your images (which depicts the shutter blocking the flash).

Now, let’s go back to high-speed sync speed and why it might be essential.

This flash mode allows you to use a faster shutter speed than the native sync speed of 1/250th second. Thus, it can eliminate the risk of overexposure and having black bars in your images.

It is essential when shooting fast-moving subjects or using a wider aperture setting in outdoor conditions. 

Temperature Control

Flash units can get extremely hot, especially under heavy and extended use. Unfortunately, some speedlights can lower power output or shut down completely when they reach such high temperatures. These are ways to protect the flash panel from damage.

You probably don’t want any of these to happen, especially when capturing a crucial scene.

Thus, it’s important to know how the flashgun handles temperature before using it on a rigorous shooting session.

Better yet, consider a speedlight with an internal temperature sensor. It allows you to control and suppress a significant increase in the temperature of the flash head for uninterrupted firing.


An external flash is one of the best accessories a photographer can own.

However, it can be pretty overwhelming to choose the right one. But as long as you keep these buying factors in mind, you might find it easier to narrow down your choices.

See some of our guides to picking flashes for specific camera bodies: Sony A7RII and Nikon D750