How to use the flash

The flash index (GN) is one of the criteria to measure the flash power. It has two functions: first, manufacturers can identify the power of the flash, and the greater the GN value, the greater the power. The second is to calculate the aperture size of flash exposure when shooting with manual flash. The formula is GN value = aperture× distance (based on ISO 100). For example, when the strobe GN value =20 (calculated in meters) and the distance from the subject is 5 meters, the aperture is set to F4 for normal exposure. When the object distance is changed to10m, the aperture should be set to F2 for effective exposure.

When the flash power is not enough, you can increase the aperture and ISO. Increasing the aperture can increase the brightness, but it will also affect the depth of field, so the method of increasing ISO is generally used to obtain more power.

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The picture shows the relationship between the aperture, ISO and distance of the flash with GN=36.

2. The role of the shutter

Flash is characterized by speed and strength. The light strikes instantly in the form of strong light, usually flashing within11000 seconds to110000 seconds. This extremely short exposure time can enter the photosensitive element through the lens much faster than the shutter speed, so generally speaking, the shutter speed does not affect the flash exposure when the aperture and output power are constant, but for example, when you shoot the same scene with115 seconds and 1/500 seconds respectively, the flash is already at/kloc-0.

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3. Flash mode

Manual mode, also used by experienced photographers, is adjusted by the formula of GN value = aperture × distance. At this time, the light output is set by the photographer according to the actual situation, which can achieve the ideal flash effect. For example, after adjusting the light transmission, use exposure lock, and then display the ambient light by adjusting the shutter speed. But the disadvantage is that each adjustment takes time, which is not conducive to snapshots.

Automatic mode. In this mode, after the aperture size of the flash and the lens is fixed (consistent), the flash will calculate whether the supplementary light is sufficient according to its own photosensitive system within the effective range of flash power, and automatically control the output size of the flash to achieve accurate exposure. At this time, the exposure can be adjusted through the aperture.

TTL mode, also belongs to automatic mode. TTL is the abbreviation of "through the lens", which means "through the lens". The way is that the light enters the light metering device of the fuselage through the lens to accurately measure the output of the flash. Canon has E-TTL and Nikon has i-TTL, all of which mean the same thing. When the shutter is triggered, the flash also triggers the supplementary light, and whether the supplementary light is sufficient is calculated by the reflected light. If underexposure is detected, the flash output will automatically increase to obtain sufficient exposure.

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4. Flash exposure compensation

Auto flash mode only gives a normal exposure, and many times we need to increase or decrease the exposure to meet the shooting needs. This is similar to adjusting the exposure compensation method of the camera. The exposure compensation on the flash can adjust the transmittance to achieve the desired effect.

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5. Flash exposure

Flash bracketing exposure (FEB) works in the same way as camera automatic bracketing exposure (AEB). In this mode, the user can select a specific exposure range (1/3, 1/2 or 1Ev). Usually, one * * will take three shots (0Ev, +Ev, -Ev), and the results will be more reliable by using the enclosed exposure.

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6. Flash zoom

Similar to lens zoom, flash zoom is to cover more areas, achieve synchronous zoom with the lens, and keep consistent with the field of view at a specific focal length of the lens. In TTL mode, the focal length of the flash will automatically match the focal length of the nearest lens. Changing the focal length of the flash will also change the projection distance and intensity of the light beam. By reducing the focal length, the light can cover a wider range and become less intense. Increase the focal length, the light beam will gather and the brightness will be stronger.

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7. High-speed synchronization

Using high-speed synchronous flash can get rid of the limitation of flash synchronization and achieve higher shutter speed, and 1/8000 can also be used. It can not only quickly solidify the moment, but also be very suitable for controlling the diving depth with large aperture. However, in this mode, the intensity of the flash will decrease, so it tends to be close to the subject.

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8. Slow synchronization

As long as the shutter is lower than the maximum synchronization speed of the camera, the flash can be synchronized with the shutter, but the longer the shutter time, the brighter the ambient light will be. In fact, slow synchronization uses the superposition of ambient light and flash. The shutter speed determines the brightness of the background, and the flash feels the brightness of the subject. Finally, the exposure of the subject and background is consistent, which conforms to the Hou Lian synchronization mentioned below. Often used for portraits at night.

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9. Hou Lian synchronization

Generally, the default state of a camera is front curtain synchronization, which flashes first when exposed. Hou Lian synchronization needs to be set, and flashes last when exposed. There is no difference between these two methods for shooting fixed objects, but there will be obvious differences for moving objects, which determines the direction of object dragging. However, Hou Lian synchronization is mainly used to shoot portraits at night. When the exposure of the background and the person is consistent, a slower shutter speed is needed. The front curtain flashes synchronously first, which makes people mistakenly think that the shooting has been completed, and once it moves, it will destroy the picture. If Hou Lian is used for synchronization, and finally the background is exposed and then flashed, the subject will not cause the fuzzy problem of the character's movements because he consciously keeps his posture.

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10. Frequency flicker

The stroboscopic function is like a machine gun, flashing frequently again and again. Strobe refers to continuous flashing and output at a certain frequency during exposure. Dozens of overlapping and patched images can be left on the screen. These images generated at regular intervals can give people a strong sense of rhythm. The frequency depends on the flash output, and the higher the output intensity, the lower the frequency.

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1 1. Off-plane flash

Off-board flash, as the name implies, is that the flash does not need to be inserted in the hot boots, and flashes in a certain range near the fuselage. Compared with being fixed on the fuselage, the off-board flash has more freedom of light distribution, and can manufacture side light, backlight and other light sources to create a three-dimensional flash lighting effect, which is often used in portrait photography.

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I hope the above points can help you understand the function of flash of antipyretic boots and inspire its use. Remember that not all flashlights have all the above functions. If you use top-class lights, that's not a problem.