========================
[Concept]
Of English, called Flash Light, to strengthen one of the ways of the exposure
Issued a strong light in a very short period of time the camera components.
========================
[Calendar history]
48 years after the birth of photography (1887) to flash photography, and its development process is roughly as follows:
------------
(1) magnesium powder flash machine (1887 ~ 1930)
Issued a strong white light ignited magnesium powder and potassium chlorate mixture, this method lasted nearly half a century.
------------
The first flash (flash bulbs). 1929 Aust Meyer (J Ostermeyer), a German invention.
------------
(3) electronic flash
Invented in 1931, on sale in 1939, which uses the gas discharge principle. Which is characterized by high-speed, economical, convenient, and is divided into three generations of products:
Between 1931 and 1939, the first generation of products, which uses a mechanical oscillator, failure-prone.
Second-generation products in the mid-1960s, which uses a transistor oscillator circuit.
Third-generation products into the market in 1972, which is characterized by:
(1) a photosensitive control circuit IC and blue silicon transistors, can automatically control based on the strength of the shooting distance and reflective flicker time (from 1/50000 to 1/120 sec.)
(2) the bypass-type changed to parallel control electronic flash to save energy, save energy, to shorten the flash gap and create the conditions for the strobe.
(3) a "hot shoe" and the other automatic contact, the speed control to the "X" position.
(4) The color temperature of 5500K, suitable for daylight-type color film shooting.
========================
[Sub 1]
---------------
A built-in flash
Use built-in flash will cause the electricity consumption of the camera and a variety of advanced features built-in flash does not support flash.
---------------
2, external flash]
External flash units are generally located in the top of the camera body, and some high-end external flash also offers a variety of advanced features.
---------------
3, handle flash]
The handle-type flash is commonly used in the studio, studio, wedding photography studios, professional place.
---------------
4, [police flash]
LED lightning series of high-definition intelligent digital flash
The product uses a unique digital control circuit has a fast call back and a long life and precise control of the flash time, continued to flash the instant high power square wave form output (power density) greatly improve the camera exposure period light output and energy.
By adjusting the flash length can make light-emitting exposure time to achieve the perfect combination with the camera, and thus greatly reduce the human eye and to minimize ambient light interference on the camera.
Able to meet in a variety of lighting conditions, the auxiliary camera system is the most clear camera requirements. Their use of the unique control technology, the effect of product performance, easy installation.
========================
[Sub 2]
Pure manual / automatic dimming / private
---------------
(1) pure manual
Flash each time the duration of the flash are the same, in order to ensure correct exposure, the operator set the aperture on the lens to subject distance
---------------
[Auto dimming formula]
The flash is the flash itself, with metering components, it can adjust itself according to the light reflected back from the subject, the flash output
---------------
(3) [special type]
Flash can only be used for a series of camera
Features is compatible with the specified camera in order to give full play to the full effect of the flash and camera TTL flash control.
Of course, there are many dedicated flash with automatic dimming device can also manually adjust.
========================
[Structure]
A lamp and reflector
2 flash lamp rotation lock button
3-assist illuminator
4 metering window
5 Mode Settings button
6 hot-shoe connection locking device
7 multiple scholars
========================
The original rationale
--------------------
1, [common type]
Common type of flash (1) refers to the energy of the flash output is adjustable flash, flash nominal flash index of GN is a constant value.
(2) The circuit consists of four parts:
Oscillation step-up part / rectifier charging part / voltage indication part / pulse to trigger the flash part.
(3) When the power is turned on, the switching characteristics of the transistor V1, the formation of an intermittent oscillation of T1 primary access to an alternating voltage, the T1 boost to the secondary access to the alternating voltage greater than 300V.
After a half-wave rectifier diode D1, an alternating voltage into a DC voltage of the main capacitor C2 and trigger capacitor C3 rechargeable energy storage.
Starter when voltage charge to about 70% of the rated voltage, indicating that the circuit of neon (Ne) indicate that the flash is in the normal flash wait state.
When you press the button to the AN, the trigger circuit (by R3, C3, T2 and Xe) pulse voltage, secondary induction in T2, the instant high voltage (10kV) pulse Xe flash tube trigger extremely Xe flash tube nitrogen ionization and conduction, the energy stored in the capacitor C2 through the flash tube discharge instantly transformed into light energy to complete a flash.
(4) built-in camera flash works as above.
When the brightness is insufficient when the outside scene, the camera's metering system will send a low according to information turned on manually or automatically by the camera flash circuit charging and flash.
Some cameras also have a system that automatically control the amount of flash (auto-dimming flash) in order to obtain a more accurate exposure.
--------------------
[Auto dimming formula]
(1) flash is fully charged, the camera flash sync contacts connected to the flash circuit.
(2) during the flash light-emitting, light from the flash exposure to the subject from the subject is reflected back to enter the camera (for exposure) and flash metering components.
This metering components will soon transform light energy into an electrical signal input integrator circuit, again from the integrating circuit output electrical signals proportional to a flash of light value;
Integral circuit of the output signal when the flash light for money to reach the requirements of the appropriate exposure control circuit to trigger the flash to stop the circuit, so that the flash is off.
(3) flash continuous flash time is very short, it dimmer used for flash metering component must have the ability to respond quickly to the photosensitive element.
(4) auto-dimming flash control mode according to the circuit structure can be divided into parallel and in series two.
(5) in the main flash tube Xe at both ends of the parallel a discharge tube V.
The main flash tube lit circuit and type the same line.
Reaches a reference value when the main flash light received by the metering components, integral circuit and control circuit to trigger the discharge pipe to discharge energy in the main control methods have not yet been immediate relief, so that the main flash tube goes out.
(6) parallel automatic dimming flash circuit structure is simple, low prices, used more often.
But each of the remaining energy of the main capacitor is not discharged all bleed finished, so charging a long time, battery consumption.
(7) series control mode is to the semiconductor switching element thyristor rectifier SCR and the main flash series in together, when the light intensity of the main flash tube output of the to achieve proper exposure of requirements thyristor rectifier SCR automatically cut off the discharge circuit and the main flash tube immediately extinguished. automatic dimming control.
Advantage
The main capacitor, the remaining energy is still preserved, which can shorten the recharge time, battery consumption is also a corresponding reduction in, quick chain lightning and recycling.
Shortcoming
The circuit is more complex and higher cost.
========================
[Use]
(1) the use of flash will be drawbacks
Shoot people, for example, the flash of light in the pupil of the eye a residual phenomenon, and thus the case of "red eye" in so many cameras will have to eliminate red-eye "this feature added to the design in speedlight to play weak light to allow the pupil to adapt to, and then run the real flash to avoid red-eye occurred.
Low or middle class digital cameras generally have three flash modes, namely, automatic flash, red-eye removal and turn off the flash.
3 products also provide "force flash" or even "slow flash" function.
========================
[Use]
The flash is a complement-ray equipment, it can guarantee a clear and bright screen shooting in dim circumstances, when shooting outdoors, the flash can also be used as a secondary light source to emphasize the skin tone. Special effects can also be arranged according to the requirements of the photographer.
1: change the color temperature.
2: To improve subject lighting conditions
3: run out of reflex, does not destroy the subject site environment
4: Add the eyes light
5: Multi-lamp combination, shape the subject's image
6: reduce or increase the contrast
7: instantaneous solidification subject
8: Fill Light
========================
【Article is excerpted from: Baidu Encyclopedia】
【Network reprint / Just reference】
【Translation is by Goolge】
