Flash memory knowledge

The knowledge of flash, I believe many people are familiar with the term flash, but not many people have a deep understanding of flash. Using flash well is a necessary skill for every photographer. If you are a photographer, you must follow me to learn about flash.

Flash knowledge 1 1, the definition of flash memory

Flash is called flash in English and electronic flash in Chinese, also called high-speed flash. The electronic flash lamp stores high-voltage electricity through the capacitor, and the pulse triggers the flash tube to discharge, thus completing the instantaneous flash. The color temperature of the usual electronic flash is about 5500K, which is close to the color temperature in the sunlight during the day. Its luminescent property belongs to cold light type, which is suitable for shooting objects that are afraid of heat.

2. Flash index

According to the explanation in the photography manual published by National Geographic, the flash index indicates the luminous intensity set by the flash manufacturer for each flash, which is usually set based on ISO 100. The flash index is usually expressed by GN, which is the abbreviation of Guild No. Its expression can be divided into two types according to the unit of meters or feet, and the calculation of GN can be calculated by the formula of "GN= aperture f value * shooting distance". Generally, the built-in flash index of 135 SLR cameras is around 12 (metric). If shooting with aperture F4, the effective flash distance is 12 ÷ 4 = 3m. When buying an external flash, it is best to buy a flash with a GN of 25 (in meters, GN/M=25) or 80 (in feet, GN/F=80), unless you take a close-up photo with ISO400. If you often take photos with reflective flash, you need a powerful flash. Buy a flash with a GN value of 40 (metric) or 130 (feet).

3, the classification of flash.

1) Built-in flash: Generally, 135 SLR cameras, APS cameras and video cameras are equipped with built-in flash, and GN varies according to different cameras. The GN of 135 SLR is about 12. In some top 135 SLR cameras, there is no built-in flash, such as Nikon's D2X and Canon's 1DS MAKR 2. Because the index is small, the built-in flash is not widely used. The place that the author uses most is to fill the light with a flash when shooting portraits. Using the built-in flash will inevitably lead to a lot of power consumption, so frequent users should always prepare spare batteries.

2) External flash: generally, it is a flash specially customized by camera manufacturers for their camera products. The characteristics of this flash are as follows: A. The flash index is large, usually between 18-56, which can be used for shooting more scenes. B. flexible use and enhanced operability. Usually, this kind of flash is connected through the camera's hot shoes or special flash socket, and those without hot shoes can be connected through the flash synchronization interface. The operation is more flexible, and it can control the output of flash quantity and change the direction of flash. Even some advanced flash lamps can be operated by wireless remote control outside the machine.

3) Large flash: Large flash is generally used in photo studios, photo studios, photography studios and other occasions. This kind of flash lamp is characterized by its extremely large output power. The flash index is not used to calculate the flash amount, but Ws (Watt/sec) is used instead. Generally speaking, 400ws is equivalent to a flash index of about 56.

4) Special flashlight: refers to an unconventional or uncommon flashlight designed for some special purposes. There are two main types:

A. Ring flash: used for close-up or macro photography, widely used in medical photography.

B. Underwater flash: As the name implies, it is used for underwater photography and has good sealing performance and pressure resistance.

4. Flash control (metering) mode:

At present, the mainstream flash control mode is TTL mode, and the corresponding flash output is determined by the actual amount of light passing through the lens. TTL is the abbreviation of (through the lens), which can be translated as "light passes through the lens". In fact, this metering determines the output of the flash in the field of view seen by the viewfinder, and the probability of failure is extremely low. On the basis of TTL, various manufacturers have developed more advanced TTL measurement mode. This paper mainly introduces Nikon's I-TTL and Canon's E-TTL.

1)E-TTL: It is another form of flash control technology released by Canon in 1995, that is, "flash metering through lens evaluation". E-TTL uses the main flash bulb to emit a low-power pre-flash with known brightness to determine the correct flash exposure. It measures the reflectivity of the scene by pre-flicker, and then calculates the output power of the flash lamp needed to realize the middle tone according to these data. Unlike TTL flash exposure meter, E-TTL sensor is not easy to be seen by curious people, and it is hidden in the case of pentaprism. E-TTL is superior to TTL and A-TTL because it is used to fill flash memory. E-TTL usually performs well by adding subtle and natural fill light flash to daytime photography. E-TTL exposure is also related to the current focus, and it is theoretically easier to obtain excellent exposure.

2) Nikon's i-TTL is similar to Canon's E-TTL. Firstly, the amount of flash is roughly estimated by pre-flash, and then the brightness of the main body at the focus position is measured. When the flash is on, the E-TTL will command the flash to stop flashing after the light shining on the main body reaches its due brightness, and Nikon's i-TTL will also substitute the distance information into the operation as a correction, and then command the flash to stop flashing, which is of course more accurate. The acquisition of this distance information is completed after the focusing is completed, so there is no time delay at all. Nikon's I-TTL has only five partitions, but because of the further correction of distance information, these five partitions are accurate enough.

5. Flashlight lighting angle:

Indicates the coverage of the light beam emitted by the flash. This is somewhat similar to the viewing angle of a lens, and it is also expressed by a focal length of several millimeters. In some high-end flashlights, there are zoom lamp holders, which can realize accurate and effective flashlight lighting according to the change of lens focal length.

6, lightning call back time

After each flash of electronic flash, the time to charge the capacitor and prepare for the next flash is called "flash back time". According to the different grades and types of flashlights, the callback time is different, and the approximate range is between 0.2- 10 second. For us, of course, the shorter the time, the better, especially when taking pictures on important occasions. Different battery types will affect the call back time. Generally speaking, the callback time of nickel-cadmium battery is faster than that of alkaline battery, and the external battery pack is faster than that of battery pack 5. Of course, the premise of choosing the battery type is that it must meet the requirements specified in the manual.

7. Red-eye prevention function

When shooting with a flash in a dark place, or when the flash is too close to people's eyes, the light beam will be reflected by the blood vessels in the fundus, leaving an annoying red pupil on the picture. In order to avoid this phenomenon, most flashlights have anti-red eye function, which can effectively avoid red eye.

8. Main flash mode

1) Fast-frequency flash: Fast-frequency flash can make moving objects leave a series of tracks, which means that the flash flashes continuously for a certain period of time. When shooting, it is best to choose manual mode, the shutter time is set above 1 sec, the background is best to choose dark color, and the all-black background is best.

2) Hou Lian synchronous flash: flash immediately before the shutter Hou Lian closes, which can avoid the illusion that the moving object stays in front of the subject when shooting at night.

3) Slow synchronous flash: In order to enhance the brightness of the background, a low-speed shutter is used to illuminate the photographed subject with a flash, and the brightness of the background is achieved through long exposure. When using slow synchronous flash, you must cooperate with tripod.

Slow synchronous flash can obtain good exposure effect of subject and background. (shooting parameters: f 7. 1. 1/4 seconds, SB-800 flash)

4) High-speed synchronous flash: High-speed flash synchronization is generally used to solidify high-speed moving objects, or to fill the light with flash when shooting against the light. With high-speed synchronization, it means that you can shoot with a large aperture flash, and you can get the effect of blurred background and prominent subject, which is widely used in portrait photography.

High-speed synchronization can use large aperture shooting to obtain good background blur effect. (shooting parameters: F2.8, 1/F2.8 seconds, SB-800 flash)

Flash knowledge 2 types of flash memory

Flashlights can be roughly divided into the following categories, and their functions and performances are different according to different types.

1, built-in flash, using the built-in flash will cause a lot of power consumption of the camera, and the built-in flash does not support various advanced functions of the flash.

2, external flash, external flash is generally located at the top of the camera fuselage, some high-end external flash also provides a variety of advanced functions.

3, handle flash, handle flash is often used in photo studios, photo studios, wedding photography studios and other professional places.

4. Electronic police flashlight: LED lightning series high-definition intelligent digital flashlight (industrial grade, model ZS-LEDSGD- 1) is a new type of high-power and high-performance digital pulse LED flashlight developed by Shangzhou Optoelectronics, which focuses on the intelligent transportation field and is used in various snapshot systems to meet the working environment and functional requirements of electronic police, such as safety bayonet, speeding snapshot, running red light and so on. The product adopts a unique digital control circuit, which has the characteristics of fast response, long service life, accurate flash time control and continuous output in the form of high power square wave (high power density), greatly improving the light output energy of the camera during exposure. By adjusting the flash length, the light and camera exposure time can be perfectly combined, thus greatly reducing the impact on human eyes and minimizing the interference of ambient light on taking pictures. It can meet the requirements of the auxiliary camera system to take the clearest photos of vehicles and drivers under various light conditions. Its unique control technology, product performance, installation convenience, service life and price are superior to ordinary flashlights. It is the best substitute for the flash commonly used by electronic police in the market at present, and it is also the first choice for the upgrading of electronic police.

5. Photo studio flash, high-power flash used in professional photography places such as photo studio, photo studio, studio, etc., generally cannot be held by hand due to factors such as weight and volume, and often stands on a special tripod or slide.