Flash photography basics

The basics of flash photography

Flash photography is a fascinating and often indispensable area of photography that allows you to take outstanding shots in almost any lighting conditions. Whether indoors or outdoors in poor lighting conditions, the correct use of a flash can make all the difference. In this blog post, you will learn about the most important terms and basic techniques of flash photography and how to use your flash optimally.

Important terms in flash photography

In order to master flash photography effectively, it is important to understand some basic terms.

TTL (Through The Lens)

TTL stands for "Through The Lens" and is a technique that enables the camera to automatically measure and set the flash exposure. The camera measures the light that falls through the lens onto the sensor and adjusts the flash output accordingly. This is particularly useful in changing light conditions, as the camera can continuously correct the exposure. This allows you to concentrate on taking photos without having to constantly adjust the flash output manually.

Guide number

The guide number is a key quality feature of clip-on flashes and indicates the maximum range of the flash at a specific aperture and ISO setting. For example, a flash with a guide number of 56 can optimally illuminate a subject ten meters away at a set aperture of f/5.6. The calculation usually refers to an ISO sensitivity of ISO 100. If the aperture is opened to f/4, the range is extended accordingly to 14 meters. Caution is advised if a manufacturer specifies a high guide number at ISO 200 instead of ISO 100. In this case, the guide number is not directly comparable and must be converted to ISO 100. The conversion factor is 1.4, so if a manufacturer specifies a flash with a guide number of 56 at ISO 200, for example, the performance of the flash unit at ISO 100 only corresponds to a guide number of 40. You should therefore always pay attention to the specified ISO value. A flash with a guide number of 56 at ISO 100 is therefore better than a flash with a guide number of 56 at ISO 200.

Flash output in watt seconds

With professional flash heads for studio and outdoor photography, the flash output is not specified in guide numbers but in watt seconds (Ws). The unit of measurement watt-second describes the amount of energy that a flash unit can emit in one second. A flash unit with the specification 500 Ws can therefore convert 500 watts of electrical energy into light in one second. More watt-seconds mean more light and therefore the possibility of illuminating larger areas or photographing with smaller apertures. Compared to the guide number, watt seconds indicate the flash output more clearly and precisely.

Modern flash units often offer the option of manually regulating the power. This gives you more control over the amount of light that hits your subject. For example, you can reduce the flash output indoors to achieve a natural lighting mood or increase the output outdoors to brighten up shadows.

Flash sync time

Die Blitzsynchronzeit ist die kürzeste Verschlusszeit, bei der der gesamte Sensor der Kamera beim Auslösen des Blitzes noch vollständig offen liegt und somit gleichmäßig belichtet werden kann. Bei Verschlusszeiten, die kürzer als die Blitzsynchronzeit sind, können Teile des Verschlussvorhangs bereits Bereiche des Sensors verdecken. Dies kann zu schwarzen Balken im Bild führen, da der Blitz in diesem Fall nicht mehr die gesamte Sensorfläche belichten kann. Die Blitzsynchronzeit variiert je nach Kamera, liegt aber typischerweise zwischen 1/200 und 1/250 Sekunden.

HSS (High-Speed Synchronization)

High-speed sync (HSS) allows the flash to be used at shutter speeds faster than the flash sync speed. This is helpful, for example, for outdoor shots with bright ambient light, as a larger aperture can be used to achieve a shallow depth of field. The HSS function also helps to achieve very fast shutter speeds of around 1/4,000 of a second for action-packed subjects where fast movements need to be frozen. HSS works by the flash emitting several pulses of light during the exposure time in order to illuminate the entire scene evenly.

Flash compensation

Flash compensation allows you to adjust the flash output in small increments to achieve optimum exposure.

This can be useful if you want to subtly vary the amount of light from the flash without having to change the camera's exposure settings.

Positive flash compensation increases the flash output, while negative flash compensation reduces the flash output. For example, if your image is slightly overexposed, you can reduce the flash output by one or two levels to achieve a balanced result.

Which camera settings are relevant for flash photography?

For successful flash photography, it is important to set the camera correctly. This includes the exposure time, aperture, ISO sensitivity, white balance and shutter curtain setting.

Exposure time

The exposure time determines how long the camera shutter remains open and light falls on the sensor. The exposure time plays an important role in flash photography as it influences the balance between ambient light and flash light. It is generally advisable not to set the exposure time shorter than the flash sync time specified by the camera manufacturer. Otherwise parts of the image will remain dark because the sensor is partially covered by the shutter curtain. If you still want to use shorter exposure times, you must switch the flash to the HSS mode described above. Conversely, you can also expose for longer than the flash sync time. In this case, you can freeze the movement of the subject with the flash on the one hand, and on the other hand create additional motion blur with the long exposure.

Aperture

The aperture controls the amount of light that falls on the camera's sensor and influences the depth of field of the image. A wide-open aperture (small f-number) produces a shallow depth of field and allows more light to fall on the sensor. A closed aperture (large f-number) increases the depth of field but reduces the amount of light. The flash output must be adjusted accordingly to avoid overexposure or underexposure. As described above under "Flash f-number", the aperture also influences the distance between the flash and the subject that can still be optimally illuminated.

ISO sensitivity

The ISO sensitivity determines how sensitively the camera sensor reacts to light. A higher ISO number means a higher sensitivity to light, which is useful when there is little light available. However, a high ISO number also leads to more image noise. If you are shooting with flash, you should keep the ISO sensitivity as low as possible to maximize image quality. In dimly lit shooting situations, however, a higher ISO sensitivity can also help to brighten the surroundings so that they do not become too dark when the flash is used.

White balance

The camera's white balance menu contains a preset for optimum color reproduction when using flash. If only a fill-in flash is used, the automatic white balance can already deliver very good results. Flash light is very similar to daylight with a color temperature of approx. 5,500 Kelvin. So if the flash is used at sunset or in rooms with warm artificial light, the difference can be clearly visible in the final shot. Although the white balance can also be adjusted in post-processing on the computer, it is advisable to take action when taking the picture. If the flash light is to be warmer in order to adapt it to warmer light sources, you can work with appropriate filter foils, which can usually be attached to the flash head using a device.

First or second shutter curtain

When photographing with flash, the flash can be synchronized to either the first or the second shutter curtain. What does this mean? The focal plane shutter of a camera essentially consists of two shutters: the first and the second shutter curtain. These movable metal plates prevent the sensor from being exposed unintentionally. Normally, the flash is triggered as soon as the first shutter curtain reveals the image chip. Probably the biggest disadvantage: any movement that takes place during further exposure is shown in the photo as a kind of superimposed motion blur.

However, many cameras and flash units also allow the flash to be synchronized to the second shutter curtain. In this case, the flash only triggers at the end of the actual exposure. Movements of the subject that took place before the flash was triggered are superimposed on the subject being flashed. This leads to a more natural picture result. However, the timing of the flash on the second shutter curtain is crucial. It can happen that the subject has already moved out of the picture frame when the camera flash triggers.

Photographing with fill-in flash

A fill-in flash can be very useful both during the day and at night to brighten up different areas of the picture. In daylight and backlight, the fill-in flash ensures that your subject does not appear as a silhouette against a bright background. This can be the case, for example, if you want to photograph people in front of a sunset. The fill-in flash highlights the person in the foreground, who would otherwise disappear in the shadows. This allows you to achieve uniform illumination of the entire image.

To do this, first switch off the flash and set the exposure on the camera so that the background of the picture is optimally exposed. The person in the foreground will then appear very dark. Only then switch the flash back on to brighten the person in the foreground. To do this, only correct the flash output and not the preset exposure for the background. The flash output can be finely adjusted either via the flash compensation or via the manual output setting for studio and outdoor flash heads until a harmoniously lit image is created.

A fill-in flash can also be useful for night shots to illuminate specific areas of the image that would otherwise be in the dark. For example, this could be a person in front of a city backdrop illuminated in the evening or at night. The same principle can also be used to brighten up details of an evening event with a flash.

Indirect flash

With indirect flash, the flash light is not aimed directly at the subject, but is reflected from the ceiling or wall.

This creates softer and more even lighting, which is particularly advantageous when taking portraits, as harsh shadows and unnatural highlights are avoided. For example, if you are photographing in a room with white walls, you can direct the flash against the wall so that the light falls softly on your subject and appears natural.

Make sure that the surface from which the light is reflected is a neutral color, as colored walls or ceilings can color the light and affect the skin tone or other colors in the image. The flash output should also be adjusted accordingly, as indirect light is less intense than direct light and may require a higher flash output. These techniques can be used indoors or in low ambient light to create professional and appealing images with natural and soft lighting.

Unleashed flash

Unleashed flash means that the flash is not located directly on the camera, but can be positioned independently. This flash method is used to create specific lighting accents and to master more complex lighting situations that would be difficult to achieve with a flash mounted on the camera. Flash units for studio or outdoor use work for this purpose either with a radio trigger, which is attached to the top of the camera's hot shoe and triggers the flash wirelessly, or with a flash cable that connects the flash to the camera, provided the camera has such a flash sync connection. Otherwise, the only other option is the radio trigger. With clip-on flashes, there is also the option of radio triggering. Alternatively, several radio flashes can also be used, whereby one is mounted on the camera and, as a so-called master flash, sends the flash settings by radio to the other flashes set as slave flashes. The advantage of radio control is that you can control several flashes separately at the same time via the radio transmitter or master flash. This is important if the flashes are to flash at different intensities.

If your camera has a built-in flash, you can also work without a master flash or radio remote control. In this case, the light emitted by the internal flash during shooting is detected by the sensors of the other flash units, which are then also triggered. It is important that no obstacles interfere with the visual contact between the camera flash and the light-sensitive sensor of the clip-on flash. With a wireless system, you are more flexible overall.

Conclusion

Flash photography offers a wide range of creative options for achieving perfect shots in all lighting conditions. If you understand and apply the basic techniques and terms such as TTL, guide number, flash output, flash sync time, HSS and flash compensation, you can take your photographic skills to a new level. Whether using fill flash, indirect flash or unleashed flash, the right technique and settings are the key to impressive images. Be adventurous and use the many possibilities of flash photography to realize your creative visions.