What Is Guide Number In Flash Photography

by -514 views

An on-photographic camera wink is an indispensible accessory for many photographers; it provides additional low-cal when weather go besides dark to handhold your camera comfortably, allows y’all to reach more balanced exposures in daylight conditions, permits freezing of fast-moving subjects and can also exist used to command or trigger other flash light sources. Additionally, a flash can be used every bit a highly constructive creative tool to plant an aesthetic that elevates your imagery when lighting atmospheric condition are considered less than stellar. The benefits of an external on-camera flash far outweigh those provided past a built-in camera flash, while the only drawback is keeping an additional piece of equipment.

On-Camera Flash versus Off-Camera Wink versus In-Photographic camera Wink

The term on-camera flash simply refers to a blazon of strobe light (wink) that can connect directly with your camera. While it is referred to as “on-photographic camera” this does not require the flash to exist physically mounted on your camera. On-camera flashes can, and often are, used off-camera. This differs from other strobe-light sources, such as studio pack strobes and monolights in that these types of strobes are not meant to be physically continued to your camera (except under rare and unusual circumstances involving convoluted methods of accommodation). Additionally, on-camera flashes normally accept a cocky-contained power supply, although external power sources tin can sometimes be used to improve performance or bombardment life.

On-camera external flash likewise refers to the type of external flash that can be used on your camera, compared to a born flash that is integrated into many cameras. An on-camera external flash performs better than a born flash in almost every regard with the one exception that it is non built into your camera. The ability to take the flash off your photographic camera results in a significantly greater number of lighting options; far more than but providing a blast of apartment light to the scene to facilitate an adequate exposure. It is ofttimes not desirable to have your flash pointed squarely at the scene at paw; more oft than not yous will desire to bounce the flash light off other surfaces and point in other directions to control the wait of your flash. When using an in-camera flash, you are forced to use the wink at the given angle from which it extends.

Near congenital-in flashes are likewise located near the camera lens, which tin can often result in the red-heart issue  when photographing subjects in dimly lit weather. Carmine-eye occurs because pupils dilate in dim light, the congenital-in flash is aligned with the lens’s optical axis, its beam enters the center and reflects back at the camera from the retina at the rear of the centre, which is quite red. Being able to use an on-photographic camera flash source off-photographic camera, from a different angle, will aid to eliminate the ruby-red-centre effect in your photographs of people.

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

Before delving into the automatic technology that is contained inside nigh gimmicky flashes, it is best to understand how to manually control and grasp a flash’s power. This is directly related to having an understanding of exposure ratios—how shutter speeds and apertures affect and balance each other—even though auto-exposure metering is available and frequently utilized for determining the best exposure settings.

Guide numbers are the standardized, numerical way of determining the power of a flash, with a college guide number representing a more powerful flash…

Guide numbers are the standardized, numerical fashion of determining the power of a wink, with a higher guide number representing a more powerful wink. 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 foursquare of the distance from the source of the physical intensity. For instance, a given intensity of light will be 1/4th the intensity at twice the distance from the source, 1/ninth the intensity at iii times the distance, 1/16th the intensity at four times the distance, and and then on. Since f/numbers fractionally relate to the intensity of an exposure, they perfectly fit into the guide number equation as a variable for determining flash exposure.

Simplifying this a scrap, a realistic example would be if yous have a flash with a guide number of 100, photographing a bailiwick 25’ away will require the use of f/4 for proper exposure. Too, a subject 50’ abroad requires f/2 or a subject v’ abroad 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 every bit ISO 800, equally a subject area 50’ away would require an discontinuity of most f/five.half-dozen. Another variable to consider is that all of these values assume y’all are using your flash at full power; often, you lot can control the flash output of your strobe in increments to either save on battery life, provide faster recycle times, or to control your exposure more than when working in closer situations. This flash power variable tin can easily be compensated for in the guide number equation by reducing ane of the other variables. For instance, if using a flash with a guide number of 100 (at ISO 100) at ane/four power and photographing a subject at 25’ abroad, you will now crave an aperture of f/2 (which is 1/4 the original example’southward given discontinuity).

ISO 100

It should also exist noted that in most instances, controlling your exposure in-camera when working with flash should only be done by modifying your aperture. This is because the precise duration of a flash is essentially less than almost shutter speeds; if y’all compensate for your exposure by using a faster shutter speed you will not see any change in exposure considering the wink is essentially performing the role of the shutter. Additionally, unless using a leaf shutter (a shutter independent within the lens, featured on many medium and big format lenses), it is likely your photographic camera’s focal plane shutter will non be capable of producing a fully-exposed epitome at shutter speeds shorter than most one/250th of a 2nd (depending on your photographic camera).

The fastest recommended speed at which your photographic camera can record an image when using flash is called the “sync speed.” If you brand an exposure faster than the sync speed while using flash, the shutter volition likely non have enough time to clear the prototype path of the sensor or motion picture while the scene is fully illuminated by the wink. This will issue in blocked or blacked-out areas of the prototype (the part of the shutter that couldn’t clear the path in time). Conversely, you lot can make exposures longer than the maximum sync speed and withal produce a fully-exposed paradigm; however, depending on this length, other consequences or benefits may occur.

Fill up-Wink and “Dragging the Shutter”

While flash is often used to illuminate a scene entirely, either because of low-light weather condition or because you are using a modest discontinuity to gain boosted depth of field, wink can as well be used in combination with ambient exposure to provide additional creative benefits. Relating back to sync speed, if you lot’re using a shutter speed that is like to what would exist required of an ambient, regular exposure, in conjunction with flash, you lot will be mixing both ambient and flash lite. This technique is chosen
dragging the shutter
and can be utilized to highlight specific objects or subjects inside a scene. An instance would be photographing a field or bush-league at dusk; while the foreground and surrounding areas are very dark, in that location is more light available in the sky regions of the scene. A way of rendering this type of scene would exist to apply your flash to illuminate the nearer regions, and then letting your shutter stay open up longer to capture the ambient light of the sky. This volition provide exposure to fairly return both the darker and brighter portions of the prototype inside a unmarried frame. Additionally, this technique works well for freezing motility in darker light; by using the flash to freeze and illuminate the moving field of study, and then keeping your shutter open to properly expose the background.

 Fill flash

Similar in concept, but using the reverse protocol, is make full flash. Fill flash is a technique in which you apply your strobe to essentially fill in areas of the scene, either because they are darker than surrounding areas or to intentionally darken the background to better illuminate a nearer subject. This technique can exist used during daylight or in well-lit situations, even if the ambient exposure is appropriate for handheld use, where there is a discrepancy between the exposure values of the foreground and background (i.e. backlit or silhouetted subjects).

To properly apply fill up flash, first meter your subject and so meter the background. This difference in exposure values is what is to be fabricated up by utilise of wink exposure. Once you lot accept adamant the difference, you fix your camera to properly expose the background values (knowingly y’all will be underexposing your subject) then you set your wink to account for the difference in stops betwixt the ii regions. This will render both areas of the image properly, giving you a more balanced, evenly lit exposure. This tool can be further manipulated to intentionally render your nearer subject area brighter than the background, to give it more prominence. In order to accomplish this, you follow the aforementioned steps as outlined before but simply set your camera’s exposure settings to purposefully underexpose the ambient regions and have the wink properly illuminate your main subject area; thus producing an prototype with a well-lit discipline and darkened background.

TTL Flash Metering

All of the previous tools and systems can effectively be utilized with your flash when set to transmission operation. By using a wink in manual way, or a flash that does not possess automatic exposure capabilities, you lot are in total control of determining both your wink’south power and your camera’s exposure settings. This is ideal for creative utilise, and becomes easier the more familiar yous are with certain working situations; notwithstanding, information technology sometimes cannot be the most practical or fastest method, considering the availability of automated flash metering. Automatic in-camera calculation of flash metering is usually washed using a TTL, or through-the-lens method. This method of determining proper wink exposure is very similar to how a camera’south exposure meter works; nonetheless, information technology takes into account more variables, such as flash power and even subject distance if used in conjunction with a compatible lens.

TTL Flash Metering

TTL wink metering initiates when the camera’southward shutter push is pressed, which then instantly triggers the connected flash. This flash then sends out a burst of light, a pre-flash, which will strike the subject and reflect back through the lens. This returning light is directed to an exposure meter, which will determine how long the true exposure should be to properly betrayal the subject field. Mod TTL systems are able to control both a camera’s and a wink’due south exposure settings to provide well-exposed results, taking much of the guesswork and experimentation out of wink photography.

This method of determining proper exposure when using flash is likewise codependent on the type of flash and camera you are using, with both variables needing to “speak the same TTL language.” Different camera types all have proprietary TTL systems, such every bit Canon’s Eastward-TTL II or Nikon’south i-TTL, and and then TTL-enabled flashes volition specify which TTL system they support. Additionally modern TTL systems will too work in conjunction with certain lenses, which further do good TTL accuracy by existence able to factor in your camera-to-discipline distance. Depending on where your focus indicate is set, the wink will deliver enough power to properly expose a discipline at that distance. For intentional over- or under-exposure when working with TTL flash metering, most flashes incorporate an exposure bounty system like to that of a camera, allowing you lot to vary the “right” corporeality of calorie-free output by a certain number of stops. Exposure compensation, likewise as dedicated settings, as well allows you to control fill up-flash amounts when working with TTL, farther enabling more than controlled and consistent flash shooting.

Billowy Your Flash and Using it Off-Photographic camera

On-camera flashes can roughly exist divided into ii classes: those that feature moving (rotating or tilting) wink heads and those that do not. The strobes that practice not have a moving flash caput have the benefit of being more compact, but outside of that their usability is significantly less than that of a strobe featuring a flash head that can tilt, and even better, one that tin can rotate. A flash with no movements is similar to an in-photographic camera flash you might already have, and when mounted on your camera, information technology volition always output light in the same foursquare, front-facing direction. These flashes do often have more ability and transmission controls than your in-camera flash, though.

However, once yous add together the ability to motion your wink caput, yous can suddenly gain much greater command and a multifariousness of options regarding how to directly the light falling on the subject. Light that is pointed direct at your subject is typically very harsh light, producing deep shadows and having a quick light fall-off from your subject area to the background (Inverse Square Law). To render a similar scene with softer calorie-free, you can tilt your wink caput to bounciness your lite off a nearby wall or the ceiling in social club to augment its directional quality. In one case the flash low-cal strikes a wall or a ceiling, that surface is being converted into a much larger light source than your wink itself. This omnidirectionality helps to lessen the furnishings of the Inverse Foursquare Law, since the light source is larger, and will produce less harsh shadows with more even lighting.

Even amend than the ability to point your photographic camera-mounted flash away from your field of study is the ability to remove your wink from the camera entirely and point information technology in any direction and at any angle you wish. This tin can be achieved in a number of means; either by way of a wired connection or a wireless connection. A wired connection only requires running a sync cord between your flash and your camera. Make certain to have a cable with uniform connections to both your camera and your flash. Flashes oftentimes accept a kind of proprietary connectedness, or sometimes also support more standardized connections such as a household plug or a miniphone, photograph, or sub-mini jack. These cables unremarkably characteristic a PC connexion at the other end to provide a connection to your camera. If your camera does not have a PC sync socket, there are as well adapters available that slip into your hot shoe and provide a PC connexion from there. Cables that connect your flash to your camera are bachelor in lengths from six” up to 33’ in either coiled or direct designs. It is best to assess how you plan to utilize your wink off-camera before deciding upon length; if information technology is as well short you lot won’t be able to become far away from the photographic camera, if too long the cablevision will get cumbersome to handle. If you’re non handholding the flash, you tin easily remove the flash from your camera and mount it to either a stand up or a wink subclass. A flash subclass enables y’all to place your flash off to the side or above the photographic camera, and commonly gives you a flake more freedom as to the orientation in which you lot can identify your flash and the direction you indicate it. Brackets typically attach to your camera from the tripod socket and provide y’all with an additional method to concur your camera/wink system.

flash bracket

The other method of tethering a flash to your camera is to apply a wireless receiver/transmitter system or a slave, which employs radio, infrared or optical triggering methods to communicate betwixt your camera and your wink. A wireless system affords yous the most artistic control, as the boundaries of how far away your flash and photographic camera tin exist are practically limitless, and you tin also work with multiple flashes for more than creative lighting setups.

Wireless Flash Control

Wireless flash is a consummate entity unto itself, but as a conference, there are essentially iii types of wireless triggers: infrared, radio and optical. Offset with the most basic, optical triggers (usually referred to as slaves or optical slaves) are a small addition to your flash that enables wireless triggering once the slave detects a flash of light. These slaves come in an assortment of connections, typically household plug, iii.5mm or 1/iv” jack, PC connection or via a hot shoe. Determine which connexion blazon is compatible with your specific flash before considering anything else when using an optical slave.

Radio remotes have the advantage of being completely non-reliant on optics and do not require a line of sight or certain lighting weather to function properly…

Once properly paired, yous simply connect the slave to your flash and utilize another flash in guild to trigger it. These are ideally used in a situation with multiple light sources, since optical slaves require one outburst of light to trigger them; however, yous can effectively use them in single-low-cal situations by programming your in-camera flash to burn down at a very low ability (1/64th or less if possible) and assume that the flash with the optical slave will completely overpower this small-scale corporeality of lite. It should also be noted that many modern flashes incorporate a built-in optical slave, which eliminates the need to add an optical slave; they are mostly for use with older flashes or in circumstances where yous might demand an especially highly sensitized slave. One other note regarding optical slaves is to account for the pre-wink that will occur when using TTL wink metering. Often, the slave will react to this pre-flash, as opposed to the intended “primary flash,” and your lighting sync will exist off. Some optical slaves have a office to automatically ignore this pre-wink, while on others, you must manually disable the pre-flash either through your camera or the chief flash you are using to trigger the optical slaves.

The other method of wireless triggering is through the utilise of an infrared or radio system. One of the main advantages of these is that you exercise non crave a difficult-wired flash in order to wirelessly trigger a grouping of flashes or even a single flash; your entire lighting setup can be controlled from a transmitter connected to your camera. When working with a wireless transmitter and receiver organisation, you will connect one unit of measurement to each flash needed and ane to your photographic camera; this provides a remote method of advice between your camera and flashes to trigger flashes, and sometimes a ways to even control the power output of individual flashes. This method can also function well if using a single unit on your camera and principal flash, then utilizing optical triggering to fix off subsequent flashes. Another do good to these triggering systems is that some flashes contain a congenital-in infrared receiver, saving you the need to attach an auxiliary one. When working with radio transmitters, information technology is less common for flashes to have congenital-in receivers, unless working with proprietary transmitters and higher-terminate flashes.

An infrared triggering system is like to an optical method, but equally the name implies, it utilizes infrared wavelengths to transmit the wink signal. This has a benefit over an optical trigger, as y’all practice non demand an on-photographic camera or directly tethered wink to trigger your exposure, which tin can affect your exposure and limit the ways of how you low-cal your image. An infrared transmitter is substantially a low-powered flash with an IR filter over the front of it; when information technology emits a burst of light, the IR filter attenuates near of this light and converts it to an infrared betoken. Infrared remotes work best in indoor situations when at that place isn’t an affluence of ambient low-cal to disrupt the infrared transmission, and they also normally crave your infrared receiver to be in straight line of sight of the infrared transmitter. With these drawbacks in mind, IR systems do accept the advantage of being able to handle extremely fast sync speeds, due to the lack of time needed to compensate for a radio manual.

The final, and most sophisticated method of wirelessly triggering flashes, is through the use of a radio transmitter and receiver arrangement. Radio remotes accept the advantage of being completely non-reliant on optics and do not require a line of sight or certain lighting atmospheric condition to function properly. They can operate across numerous channels, which profoundly enhances photographing with wireless flash in situations where multiple photographers are working. Their other master benefit is that some radio systems integrate full TTL compatibility, which gives direct connection betwixt the flash and your camera for controlling wink exposure. Many radio slaves also have dual functionality, deeming them transceivers, which allows the same units to exist placed on either cameras or flashes. Transceivers tin usually exist set to transmit or receive, which helps to further dial in the specific purpose of them under certain circumstances.

Additional Battery Ability

As previously mentioned, one of the defining characteristics of an on-camera flash is a cocky-contained ability source. This power source, often AA batteries, is stored inside the flash and tin can be replaced easily during the grade of a photo session. This convenience is certainly appealing when compared to portable strobe packs featuring batteries that alone can weigh more than twenty lb; however, AA batteries are also not that powerful. Flash is a power-craving tool that requires battery power and quantity in excess of typical camera batteries. Rather than favoring a dependency on numerous AA batteries, it is benign to use an external battery pack if you use wink on a regular basis. Auxiliary battery packs are often compact in size, for carrying in a pocket or attaching to a belt, and connect to your wink via a dedicated cablevision. Packs contain an internal, rechargeable battery; a removable, rechargeable battery; or in some instances, are merely a means to parcel several AA or other common battery blazon together to more efficiently provide longer battery life versus irresolute out batteries from the wink itself. In improver to longer battery life, battery packs also ofttimes allow for faster recycle times—meaning yous tin burn down your flash more rapidly with less time in between bursts. Ofttimes only higher-finish flashes will back up the employ of an external battery pack, since they are more than typically put through longer shooting times and more strenuous weather condition.

Bolt CBP-C1 Compact Battery Pack for Select Canon & Bolt VX Series Flashes

Other Features to Look for When Purchasing a Flash

Equally information technology would when looking for whatsoever other photographic camera equipment, purchasing a flash should exist heavily dependent on your needs to ensure information technology has the features you lot will use and will best suit the applications for which you intend to utilise it. Additionally, information technology is usually preferable to work with a flash all-time suited to the specific photographic camera type you use, either by fashion of using the same brand or a third-party manufacturer with photographic camera-compatible accessories and connections. This is especially prevalent in regard to TTL systems, with not all TTL-uniform devices beingness TTL-compatible with your specific camera or flash. Like cameras, too, flash option should also take into account the build quality and how it will withstand the weather in which you typically work. Certain flashes feature full atmospheric condition-sealing, which could be necessary for working in adverse weather condition.

Flash Accessories and Light Modifiers

As mentioned previously, when talking about bouncing flash and getting the wink off your camera, is that a flash’s artificial light and straightforward angle are often non the near flattering or aesthetic sources. In improver to directing your light source at something other than your discipline, you tin can likewise apply numerous other tools to bear upon the mode the low-cal strikes your bailiwick. These on-photographic camera light modifiers come in a wide array of shapes and sizes, all serving to alter your light in various ways.


The nearly mutual type of add-on light modifier for your flash is a diffuser, in either bounce, apartment, dome, or wide-angle styles. These diffusers work by placing a translucent box or substrate in front of your flash, helping to soften and spread the calorie-free a bit more than evenly than an undiffused flash head. You will likely lose at least one cease of power from your flash, but your calorie-free will have less directionality and more of a softer, less loftier-key appearance.

Mini Softboxes

A mini softbox, equally the proper name suggests, is a smaller version of a softbox that is designed especially for use with an on-camera flash. A softbox converts your wink into a larger, softer calorie-free source to help lessen the intensity of shadows and produce a more than wrapped-light quality. The differently shaped softboxes volition produce differently shaped catch lights in subjects’ eyes; otherwise the different shapes will role similarly based on respective dimensions or expanse of the softbox.

Bounciness Cards

Many flashes feature a congenital-in bounciness card that slides out over the flash head, but if not or for more than control and adaptability, auxiliary bounce cards are available. In terms of light quality, a bounce card is something between a diffuser and a soft box. Information technology produces light akin to bouncing your wink off the ceiling or a wall. These reflector cards extend from the superlative of your wink head and cake light from spilling in all directions, and after create a larger, softer light source.

Grids and Honeycombs

Grids afford more control and a tighter lite output from your flash. The honeycomb pattern helps to limit the overall spread of lite and concentrate it into a more organized beam. Grids are oftentimes available in an assortment of sizes or degrees, with the smaller measurements referring to a tighter, more refined light spread.


For an even narrower beam of light than a grid, a snoot tin can be used to create a small circle of light. The longer the snoot, the smaller the circle of lite will be. Additionally, snoots oft feature an fastened filigree spot at the terminate for an even narrower beam angle. Both grids and snoots, and a combination of the two, will produce a harder light quality, greater dissimilarity, and more dramatic shadows due to their limiting of the low-cal spread.


A flash extender is essentially a Fresnel lens that concentrates the flash light into a tighter beam to exist thrown at greater distances. It is like to the idea of a telephoto lens for your flash, and some flashes even have telephoto/Fresnel lenses built into them to serve this purpose. An extender is different than a snoot in that it does not merely restrict the light from spilling; instead information technology focuses the light into a tighter area to simulate the angle of view of longer lenses.

Color Filters and Gels

Color filters and gels are used over your wink head to alter the color of light being produced. Most flashes emit low-cal that is daylight-counterbalanced (between 5000 and 6000K), which is fine for general purposes. When working under mixed-lighting conditions, still, such as fluorescent or tungsten-lit rooms, the difference in the color of light between your wink and the ambience lighting volition be much more than credible. Past roofing your flash with a colored gel, yous tin can more closely gauge the surrounding color temperature for more than balanced lighting. These filters, oftentimes sold in kits or packs, can incorporate a range of colors that typically include CTB (color temperature blue) and CTO (color temperature orange) filters.

These specific filters, and more often the CTO, are oftentimes used to balance your strobe’s light accordingly; a full CTO volition convert your flash light to approximately 3200K for tungsten lighting, and a full CTB will catechumen it to approximately 5600K for daylight utilise (if using a flash that is not already balanced for daylight). For more information on balancing mixed lighting conditions, refer to this B&H In Depth commodity. Additionally, many of these kits include many other colors to choose from for more creative applications where you want to use a colored lite source every bit opposed to one appearing “white.” These filters and gels can be affixed to your flash in a large variety of ways, ranging from defended filter holders for your specific flash to simply taping the gel over the flash head.

Ringlights and Macro Lighting

I other specialized blazon of lighting is an on-photographic camera ringlight, and other types of on-photographic camera lighting well-suited to macro applications. While all ringlights are technically “on-camera,” these refer to those that feature self-contained ability and other features as noted before. A ringlight is a unique lighting tool that is donut-shaped and goes directly effectually your lens. This round calorie-free is perfectly aligned with the axis of your lens and helps to provide most shadowless lighting, since the light is coming from all angles direct surrounding the lens. When used with more powerful studio strobe battery packs, a ringlight is a popular tool for fashion and portraiture work, but when confined to an on-photographic camera source the low-cal output is typically fairly limited and best suited to macro and close-upwards applications. The other, and even more important, reason that ringlights are best suited to macro work is that they plant an effective solution that provides even lighting to subjects where your ain or your camera’southward shadow would be in the manner if y’all were using off-camera lighting. Since the calorie-free is positioned on the same plane as your lens, you are able to light anything that your lens can focus on. In improver to ringlights, there are also twin-light setups that position 2 carve up light heads off to either side of your lens, but however on a similar plane as your lens. These dual heads can be positioned to induce a more physical, 3D quality than a ring flash since they can exist tilted or moved slightly to create more than dimensionality with objects. Finally, in that location are also twin-lite setups that are fastened to a ringlight to provide the benefits of both systems, including the flat, fifty-fifty lighting of a ringlight but with the bachelor dimensionality of a twin-low-cal configuration.

Ringlights and Macro Lighting

Flash is an entire co-existent realm to available-calorie-free photography, and can be utilized to better highlight or requite a more interesting visual advent to subjects. Flash tin can provide additional dimensionality and texture to subjects in a way that cannot be achieved with natural low-cal. An on-camera flash is a applied and lightweight option for using additional light when making photographs, and serves to be much more expansive than a flash that is simply confined to be atop your camera. When used in conjunction with controlling the power output, light direction, placement, shape and colour of the lite output, an on-camera flash is undeniably an of import tool to take for many, if non all, photographers.

If you take any questions or concerns near flash photography and what equipment is right for yous, please contact a B&H Sales Professional person via live chat, over the phone or in our SuperStore.

Source: https://www.bhphotovideo.com/explora/photography/buying-guide/guide-camera-flash

Posted by: Fusiontr.com

Originally posted 2022-02-12 11:40:01.