A Guide to On-Camera Flash

A Guide to On-Camera Flash

An on-camera flash is an indispensable accessory for many photographers. While it provides light to supplement dark conditions, an on-camera flash also allows you to achieve more balanced exposures in daylight conditions, permits freezing of fast-moving subjects, and can even be used to control other flash light sources. With so much to offer, an on-camera flash can become an integral part of your workflow, but where do you start? We are going to give you the on-camera flash rundown with everything you need to know to make the most of this important tool.

On-Camera Flash vs. In-Camera Flash

An on-camera flash is, quite simply, a type of strobe light that connects directly to your camera. While it is “on-camera” by name, this type of flash can be used interchangeably on or off-camera, affording users greater control and better lighting options. These lights notably have their own power supply, and many can accommodate external power sources to improve their overall performance.

You might be wondering why an on-camera flash is more appealing than the built-in flash on your camera. While that in-camera flash might suffice for illuminating a dark environment, it is less than ideal to have your flash pointed squarely at the scene at hand. Because the built-in flash is stationary, you cannot control or direct it by angling or bouncing the flash off different surfaces, resulting in a final result that isn't quite what you envisioned. Additionally, its location near the camera lens often produces the red-eye effect when photographing subjects in dimly lit conditions. Sure, you can edit that in post-production, but there’s only so much you can do to remedy overall bad lighting after the shoot is over. By contrast, on-camera flashes can be tilted and swiveled, or taken off the camera completely for a more aesthetically pleasing effect. 

Guide Numbers, Manual Usage, Controlling Flash Power, and Sync Speeds

In general, understanding how to control an on-camera flash manually is the easiest way to integrate this nifty little gadget into your workflow. While auto-exposure metering is available and useful for determining the best exposure settings, you should know the ins and outs of your flash to truly make the most of it. 

We will start with guide numbers, which are the standardized quantification of a flash’s power, with a higher guide number representing a more powerful flash. A guide number is the product of multiplying the f/stop of an exposure with a given distance, at ISO 100; or GN = f/number x distance. This calculation directly refers to the Inverse Square Law, which states that a specified physical intensity of light is inversely proportional to the square of the distance from the source of the physical intensity.

For example, a given intensity of light will be 1/4 the intensity at twice the distance from the source, 1/9 the intensity at three times the distance, 1/16 the intensity at four times the distance, and so on. Since f/numbers fractionally relate to the intensity of an exposure, they fit perfectly into the guide number equation as a variable for determining flash exposure.

Let’s simplify this a bit with a real-life example: If you have a flash with a guide number of 100, photographing a subject 25' away will require the use of f/4 for proper exposure. Likewise, a subject 50' away requires f/2 or a subject 5' away requires approximately f/22. Since guide numbers are typically expressed at ISO 100, you can further determine your exposure if using a higher sensitivity, such as ISO 800, as a subject 50' away would require an aperture of about f/5.6.

Of course, these examples assume that you are using your flash at full power. You might opt to control the flash output of your strobe in increments to reserve your battery life, achieve faster recycle times, or to attune your exposure when working in closer situations. This variable fits into the guide number equation by reducing one of the other variables. For instance, if using a flash with a guide number of 100 (at ISO 100) at 1/4 power and photographing a subject at 25' away, you will now require an aperture of f/2 (which is 1/4 of the original example’s given aperture).

It bears mentioning that, when working with a flash, controlling your exposure in-camera should only be done by modifying your aperture. Because the precise duration of a flash is substantially less than most shutter speeds, you will not see any change if you compensate for your exposure by using a faster shutter speed, because the flash is essentially performing the role of the shutter.

This brings us to sync speed, which is the fastest recommended speed at which your camera can record an image when using flash. If you make an exposure faster than the sync speed while using flash, the shutter will likely not have enough time to clear the image path, resulting in a partially blocked or blacked-out image.


Fill Flash and “Dragging the Shutter”

While flash is often used to illuminate a scene entirely, it can also be used in tandem with ambient exposure for creative effects. Known as “dragging the shutter,” this technique uses a shutter speed would be required of an ambient exposure with your flash to mix both ambient and flash light. Essentially, by adjusting your sync speed, you can highlight specific elements in a scene.

Let’s say you are photographing a field or bush at dusk. While the foreground and surrounding areas are very dark, the sky still provides some light in your scene. You could use your flash to illuminate the foreground while keeping your shutter open longer to capture the ambient light of the sky. This will adequately expose the darker and brighter areas of the scene in a single frame. This technique also works well for freezing movement in darker light, where the flash captures the moving subject while the open shutter properly exposes the background.

Fill flash

Reversely, “fill flash” can be used to illuminate a nearer subject while keeping the background darker as the flash light falls off. This technique can be used in well-lit or daylight situations and is useful when your subject is backlit or silhouetted.

To use fill flash most efficiently, you will want to meter both your subject and background. Taking the difference of those exposure values, set your camera to expose the background values properly (underexposing your subject) and set your flash to compensate for the difference in stops between your background and subject. This will render both areas of the image properly, giving you a more balanced, evenly lit exposure.

You can also use this technique intentionally to render your nearer subject brighter than the background, giving it more prominence. Simply follow the same steps outlined above, but set your camera’s exposure settings to underexpose the ambient regions while the flash illuminates your main subject.

TTL Flash Metering

While ideal for creative use, manual flashes are sometimes not the fastest or most practical, depending on your application. This is where automatic flash metering comes into play.

Automatic in-camera calculation of flash metering is usually done using a TTL, or through-the-lens method. This method of determining proper flash exposure is very similar to how a camera’s exposure meter works, but it accounts for more variables, including flash power and subject distance when used with a compatible lens.

TTL flash metering initiates when you press the shutter button on your camera, triggering the connected flash. A burst of light called a pre-flash then engulfs your subject and reflects back through your lens. This returning light is directed to an exposure meter, which will determine how long the true exposure should be to expose your subject properly. This light can be corrected if you are looking to over- or underexpose your subject, making for a more controlled and consistent shooting experience. Overall, TTL flash metering avoids much of the guesswork and experimentation you can expect when working with a manual flash.

As you may have noticed, different camera types often have proprietary TTL systems, such as Canon’s E-TTL II or Nikon’s i-TTL. Many modern TTL systems are even optimized for specific lenses, allowing users to reap the benefits of more powerful TTL. Luckily, users of specific systems aren’t relegated to any one manufacturer for an on-camera flash, since most name-brand and third-party manufacturers offer flashes that support multiple TTL systems.

Bouncing Your Flash

We’ve mentioned flexibility as one of the main draws of an on-camera flash, in part because they can be adjusted and moved around. While there are stationary flash heads, they offer little outside of compactness over their adjustable counterparts. Rotating and tilting are the most common adjustments you can expect from an adjustable flash head, providing better control and variety to achieve your desired lighting effect.

Bouncing Your Flash and Using it Off-Camera

Light that is pointed directly at your subject tends to be harsh, producing deep shadows and a steep, undesirable light fall-off. With an adjustable flash head, you can tilt or rotate your light to bounce off a nearby wall or the ceiling, broadening its directional quality and softening the overall cast. You can enhance this effect with flash accessories like light modifiers and bounce cards, but more on that later.

Wired Flash Control

While mounting is great, on-camera flashes are especially flexible because they can function apart from your camera. Using either a wired or wireless connection, you can deploy an on-camera flash pointing in any direction or angle you wish. A wired connection requires a sync cord between your flash and your camera, typically via your camera’s PC sync socket or an adapter. While some flashes support more standardized connections like a household plug or a sub-mini jack, others require their own proprietary connection, so take care to ensure everything is compatible.

Cables for a wired connection vary in length and design, so it is best to assess your off-camera configuration first before buying one. You might want a shorter cable if you don’t plan to stray too far from your camera, or a longer cable to allow more distance.

Other accessories, like stands and flash brackets, make using your flash off-camera easier when you don’t want to hold it in your hand. While a stand can be placed anywhere, a flash bracket will position your on-camera flash just above or to the side of your camera, offering a bit more freedom to orient the flash apart from the camera itself.

Wireless Flash Control

Wireless flash is a bit more complicated than wired flash, with three different types: infrared, radio, and optical. Optical triggering, the most basic of the three types, works best in multi-light configurations. Often referred to as slaves or optical slaves, lights with optical triggering activate when they detect a flash of light. Like wired on-camera lights, slaves come in an assortment of connections and will require compatibility with your specific flash. Once properly paired, connect the slave to your flash and utilize another flash to trigger it.

While they are best in multi-light configurations, optical slaves can be used in a single-light capacity by programming your in-camera flash to fire at a very low power (1/64 or less if possible) and allowing the optical slave to overpower it completely. It is also worth noting that optical slaves can be problematic when using TTL flash metering. Often, the slave will react to the pre-flash, triggering before the main flash and throwing off your lighting synchronicity. While some optical slaves can automatically ignore the pre-flash, others will require you to disable it manually, via your camera or your master flash.

The second method, infrared triggering, utilizes infrared wavelengths to transmit the flash signal. You might prefer this method over an optical trigger because it doesn’t require an on-camera or directly tethered flash to trigger your exposure. An infrared transmitter is essentially a low-powered flash with an IR filter over the front of it; when it emits a burst of light, the IR filter attenuates most of this light and converts it to an infrared signal. One drawback to consider is that infrared remotes work best in indoor situations where there is less ambient light to disrupt the infrared transmission. They also usually require a direct line of sight to work, making triggering difficult if you are working in confined spaces or among obstacles. With these drawbacks in mind, IR systems do have the advantage of handling extremely fast sync speeds because they require less time to compensate for a radio transmission.

The last and most sophisticated method is radio triggering. Radio remotes have the advantage of being completely non-reliant on optics and do not require a line of sight or specific lighting conditions to function properly. They can operate across numerous channels, making wireless flash possible even with multiple photographers working simultaneously. Some radio systems even have full TTL compatibility, providing a direct connection between the flash and your camera to control your flash exposure. Additionally, many radio slaves can function as transceivers, allowing the same units to be placed on either cameras or flashes. This duality makes a radio triggering system more versatile under certain circumstances.

Additional Battery Power

Earlier, we mentioned how on-camera flashes benefit from having a self-contained power source, usually AA batteries. By contrast, your typical portable strobe pack might require batteries that weigh upward of 20 lb. The real tradeoff here is power―with flash consuming more than your regular batteries can dish out. Because of this, you might opt for an external battery pack, especially if you use flash on a regular basis. In addition to longer battery life, battery packs often enable faster recycling times, allowing you to fire your flash rapidly with less time between bursts. Auxiliary battery packs, which connect to your flash via a dedicated cable, tend to be compact enough to carry in your pocket. If you really plan to put your on-camera flash to work, you might look at higher-end flashes that will support the use of an external battery pack, since they are designed with longer shooting times and more strenuous conditions in mind.

Other Features to Look for When Purchasing a Flash

Like any purchase, it is important to consider how you will use your on-camera flash. Of course, you will want a flash that is compatible with your camera, especially when dealing with TTL. You will also want to get a flash that is proportional to your camera in size and weight. Other factors, like triggering methods and overall build quality, will determine whether an on-camera flash will be a worthy long-term lighting solution. If you plan to work outside, you might want to get a weather-sealed flash that will withstand adverse conditions.

Flash Accessories and Light Modifiers

There are many ways to outfit your on-camera flash to achieve your desired lighting effect. We are going to highlight the most widely used light modifiers, and why they might be conducive to your artistic goals.

  • Diffusers are one of the most common types of light modifiers, available in bounce, flat, dome, or wide-angle styles. By placing a translucent box or substrate in front of your flash, a diffuser will soften and spread the light more evenly than an undiffused flash head. While you will likely lose at least one stop of flash power your light will have less directionality and a softer appearance.

  • Mini Softboxes are a smaller version of a softbox designed for an on-camera flash. This accessory enlarges and softens your light source, lessening the intensity of shadows and producing a more wrapped-light quality. Available in different shapes, mini softboxes can also be used to create unique catchlights in subjects’ eyes.

  • Bounce Cards function as reflectors, producing a larger, softer light effect much like bouncing your flash off a ceiling or wall. Many flashes feature a built-in bounce card that slides out over the flash head, blocking light from spilling in all directions.

  • Grids and Honeycombs are used to control your flash. Whereas grids provide a tighter light output, honeycombs limit the overall spread of light, concentrating it into a more organized beam. Grids are often available in an assortment of sizes or degrees, with the smaller measurements a tighter, more refined light spread.

  • Snoots can be used to achieve an even narrower beam of light than a grid. This accessory produces a small circle of light, with a longer snoot creating a tighter circle. Grids can be affixed to snoots, producing an extremely narrow beam angle with a harder light quality, greater contrast, and more dramatic shadows.

  • Extenders concentrate the flash light into a tighter beam to be thrown great distances, almost like a telephoto or Fresnel lens for your flash. Unlike snoots, which restrict light to prevent spilling, extenders focus the light into a tighter area to simulate the angle of view of longer lenses.

  • Color Filters and Gels are applied over your flash head to alter your light’s color. They are useful when working under mixed lighting, such as fluorescent or tungsten-lit rooms, by getting closer to the room’s approximate color temperature for more balanced lighting. Filters and gels often come in packs, containing practical colors to address color temperature disparities, or vibrant colors with which to experiment.

Ringlights and Macro Lighting

Ringlights are a specialized form of on-camera lights that are designed for macro applications. While they embody many of the same qualities as standard on-camera lights, ringlights are donut-shaped and are mounted directly around your lens. Because the light source is perfectly aligned with the axis of the camera lens, users can enjoy nearly shadow-less lighting in macro and close-up applications. This also helps prevent your own camera’s shadow from getting in the way while working.

In addition to ringlights, there are also twin-light setups that position two separate light heads off to either side of your lens while remaining on a similar plane. These dual heads can be positioned to induce a more physical, 3D quality than a ring flash since they can be tilted or moved slightly to create more dimensionality with objects. There are even twin-light setups that feature a ringlight to provide the benefits of both systems—the flat, even lighting of a ringlight and the dimensionality of a twin-light configuration.

Incorporating flash into your photography is one of the most important steps you can take to mature and develop your craft. With the addition of an on-camera flash, you can access untold creative control practically and conveniently, reaching far beyond what any in-camera flash can offer. With the more intimidating technical aspects of an on-camera flash demystified, we hope that you can pursue your own photography more confidently. You can always contact a B&H Sales Professional via live chat, over the phone, or in our SuperStore with any questions.

Do you have any tips for working with an on-camera flash? Let us know in the Comments section, below.


Great article. While I use my Nikon SB-600 and SB-400 with my DSLR's, I occasionally - like when I'm in a retro mood - use my old Vivitar 272 (that's right 272!) flash with my old YashicaMat 124G, my old Gossen C-mate light meter, and my home-made flash bracket. The Vivitar flash uses two 9 volt batteries, and it still works!! Not exactly auto-everything, but it is fun.

This article is very informative and covers the most important information to make a sound decision at the time of flash purchase.  Thanks so much!!

I just started college for my General Studies but i intend to go for photography what would be the best colllege for that??

I've just started at university doing a Commercial Photography degree and we had a fill in flash/dramatic flash class on Friday which I struggled with to be honest but finding this article has really helped me to understand the process, many thanks!

Many thanks for such an awesome article. Simple and straight to the point. Please keep up the good work.

Nice! You covered my whole career in photography. I started with a Speed Graphic with a flash bulb "gun" (#5 or #11) attached to the side that could be hand-held separately and raised to tilt down on the subject to give modeling and cast the shadow down and out of the picture. Today, I carry a Point & Shoot with a built-in "trigger" flash that activates a separate slave unit. I skipped the DSLR phase in my retirement. Thanks again!

Thank you so much for the detailed description of external flashes. You know expectations never die.....it would be nice if more pictorial / graphical examples are given for 'dragging the flash' & some flashes compared technically.

But it is a really awsome article bjorn...

Thank you for a very simple explanation for a very complex process. This is where you use that math that you always said you would never use

Thank you very much! This was eactly what I was looking for.

I see most monolights hide the GUIDE NUMBER and brag about the Watt/S, most are 56 to 78 ....I found a $99.00 dollar one 160W/S with an output of @100 ISO (150 GN) how can that be when $600 dollor light are only 78

Well it would be difficult to make a fair comparison without knowing which studio strobe is being compared to the 160 w/s strobe you mentioned. The higher price point on most studio strobes not only has to do with the amount of energy they can store and release, but it has much to do with the control they offer in terms of the f-stop range and modification of the light.  Additionally, if the studio strobe may offer different readings of light output depending on how you actually modify it.  For example, a hard reflector with a silver surface might give you more output with a studio strobe versus using an umbrella with a silver surface on the same type of strobe.  If you would like a more specific comparison, please indicate the make and model of each strobe in question. 

Thankyou it help me, to buy a flash light

Very useful info

like it vey much.

I've never owned a Flash of any kind, I've always relied on the natural light. After digesting the good information in this post my thoughts have changed and will now consider the purchase of an on-camera flash. Thanks for such a good article!

Awesome article! Extensive and well done. This will greatly help me in my search for an on-camera flash. Thank you, Bjorn!

Great article, answered all my questions

Thank You so much!!!!