Main types of flash photography

Intermittent artificial lighting-flash and electronic flash (i.e. strong light) lighting.

The English scientific name of flashlight is flashlight. Flash is also one of the ways to enhance exposure, especially in dim places, which helps to make the scenery brighter. There are also disadvantages to using flash. For example, when shooting people, the light of the flash may remain in the pupil of the eye, and then "red eye" will appear. Therefore, many camera manufacturers have added the function of eliminating red eye in their designs, and before turning on the flash, they will use weak light to adapt to the pupil, and then carry out real flash to avoid red eye. Generally, there are three flash modes for middle and low-grade digital cameras, namely, automatic flash, red eye removal and off flash. More advanced products also provide "forced flash" or even "slow flash" function.

Light is light, whether it comes from the sun, stray light, flash or electronic flash. The fundamental difference between continuous astigmatism lighting and intermittent flash or frequency flash lighting lies in the duration of light. Astigmatism lighting is continuous from before exposure, during exposure to completion of exposure; Flash or flash only emits strong light during exposure.

Of course, they are no different in other aspects, such as the heat of light, the color of light and so on. But the main difference is the duration of light.

Technical terms-electronic flash and strongpoint first, briefly explain the words strongpoint and electronic flash.

Strongpoint is actually the abbreviation of stroboscopic discharge tube. Stroboscopic discharge tube is an electronic light source that can repeat high-speed flash almost continuously. It is used to photograph golf players' hitting movements and fast movements that are difficult for the eyes to catch, such as bullets in flight. The stroboscopic discharge device can flash continuously for more than 20000 times in 1 second.

Electronic flash is used for general photography, which is different from strongpoint. After each flash, the electronic flash must wait for a period of time to charge the capacitor before flashing again.

Because the general electronic flash for photography is the result of early stroboscopic discharge experiments, the word strongpoint is gradually widely used to represent all electronic flash. After years of lax use, most photographers think strongpoint is an electronic flash. In this lesson, we will use the words strongpoint and electronic flash alternately according to our habits. Because people have generally accepted this usage.

Electronic flash

Flash bulb is also the most important portable photographic light source, and the background sound caused by flash explosion can often be heard at the press conference. Now, professional photographers have replaced the flash bulb with a lighter electronic flash. The reason is obvious:

1. The electronic flash device can be used repeatedly and can flash for thousands of times, saving the time of changing light bulbs after each shooting and the cost of carrying many light bulbs with you.

2. The flash duration of peak intensity is very short. The average electronic flash device only takes 1/50000 seconds, while the average flash bulb takes about 1/200 seconds.

3. The flash intensity can be controlled electronically, and it can be enhanced or weakened by turning on the switch on the electronic flash device.

4. The electronic circuit can automatically control the amount of flash. When we shoot in focus, the flash will automatically release a proper amount of flash.

Electronic flash is also called high-speed flash, strobe flash or strong light flash. As mentioned earlier, we can also use the word strongpoint. The stroboscope can be powered by battery or household AC power supply. The battery can be an ordinary flash battery, but it can't be used after a certain number of flash charges; You can also use nickel-cadmium batteries charged by household AC power supply. For small stroboscopic devices, the battery is installed in the flash housing; For large stroboscopic equipment, the battery can be installed in an independent power box together with other electronic components.

The battery can charge the capacitor and accumulate high voltage charge. When a strong point flashes, the accumulated charge flows into the gas-filled flash tube under the action of potential difference, which excites the gas and instantly releases bright light. Most of the strobe devices dedicated to photography studios can also be powered by household alternating current, just like very portable strobe devices. The voltage of110v (220v in China) is raised to high voltage through the transformer in the flash device.

Whether using batteries or alternating current, it takes some time to charge the capacitor after a flash. The time taken for this charging process varies with the flash device and power supply. It usually takes only a few seconds to complete the charging process by using alternating current or new dry batteries. The longer the battery is used, the longer the charging time will be. For rechargeable nickel-cadmium batteries, plug strongpoint into a matching small charger and plug the charger into an AC power outlet. Once the battery is fully charged, the charging time can be shortened to a few seconds. In the past, it usually took 24 hours to charge the battery once, but now it can be completed by fast charging 1 hour.

Some professional stroboscopic devices can take the nickel-cadmium battery out of the flash and charge it. The advantage of this is that professional photographers can put on another fully charged nickel-cadmium battery and continue to work, instead of waiting for the original battery to be fully charged or using another flash to continue shooting. You can imagine how valuable it is in some occasions, such as wedding scenes, news events, sports events and so on. In these shooting occasions, we are not allowed to say: wait a minute, wait until my battery is fully charged.

Automatic exposure frequency flash

The advantage we are using now may be the automatic exposure mode. How does it realize automatic exposure? Speaking of it, this should be a small miracle of modern electronics. In essence, the automatic stroboscopic device works as follows:

At the moment when the strong point flashes, the photosensitive element installed in the flash device measures the light reflected by the object, as shown in figure 12.7. When the light that irradiates the object is exposed normally enough, the photosensitive element excites the complex electronic circuit to close the strong point. The greater the amount of light required for normal exposure of the subject, the longer the duration of the flash.

This sounds simple, but it is not so easy to decide whether to turn off the flash in as short as 1/50000 seconds. For example, in the popular stroboscope, the shortest exposure time is exactly 1/50000 seconds, and the longest exposure time is only11000 seconds. The electronic circuit must choose the appropriate time to turn off the flash within these two limited times.

When using auto-zoom, be sure to look at the dial on the back of the device carefully, and find out the F aperture that should be used when shooting on the dial according to the asa sensitivity of the film used. Set the aperture according to the found value, and then shoot the subject within the effective range of the flash. The manual of the flash will specify its effective range, such as 4 ~ 30 feet (about 1.2 ~9 meters).

It must be noted that this automatic function is reliable only under so-called normal conditions. When using this system, we must clearly understand what the photosensitive element measures. For example, when we shoot a small dark coin on a white desktop, the light sensor reads the light reflected from the white desktop, so the dark coin will be underexposed. For this reason, most automatic strobes have manual function, so we can avoid its automatic function.

Special flash

Special flash refers to a flash device specially designed for a specific type of camera, so that it can communicate with the camera in electronic form. For example, for a special flash, all we do is turn on the power switch on the flash. The camera can automatically set its correct synchronization speed and automatically set the aperture according to the correct film speed. In the viewfinder of the camera, when the flash is charging, one of the indicators will light up. If another indicator light is also on before each shooting, it means that the light irradiated on the subject is enough (for the sake of distinction, we call the latter indicator light the confirmation light). The combination system of special flash and camera can complete some or all of the above functions, and now it has gradually developed into a convenient and practical fool series. By the way, the full name of the indicator light is light-emitting diode, and the English abbreviation is led. Led can emit a little red light, green light or white light in the viewfinder, telling us that the image has been exposed normally, the focal length has been adjusted, the flash has been charged, or other important information.

For some automatic exposure cameras, the measurement of the flash is not directly measured by the sensor of strongpoint, but measured on the actual film plane in the camera. This is the so-called ttl (through the lens) flash measurement, which gives people more convenience and broadens our new horizons. As we know, for the traditional automatic strong spot, the optical sensor measures the approximate reading of the light that should be projected on the film plane, and the measurement result may be inaccurate for the following reasons. First of all, due to parallax, the light measured by the sensor at close range may be different from the light actually projected on the film. Secondly, the actual amount of light passing through the lens may be more or less than the amount of light that should be indicated by the flash. Sometimes this error can be as high as full aperture, but the sensor of strongpoint still thinks that the lens and aperture are completely correct. In ttl photometry, the actual working aperture is measured on the film plane. Third, accessories such as filters and leather cavities will reduce the amount of light projected onto the film. However, the sensor of the flash will not be intelligently compensated. Ttl measurement system can compensate for the weakened light. Based on the above three points, special flash can provide more accurate exposure than ordinary flash. In addition, the special flash has many advantages. Ordinary automatic highlights require us to shoot with a specific F-stop, such as f/8. What should I do if I want to use f/2 selective focusing or f/6 maximum depth of field? If we use ordinary flash, then we can only choose the aperture in a limited way. However, if you use special flash and ae camera (that is, automatic exposure camera), you can choose any aperture and let ttl metering system control the flash duration. The combination of special flash and ae photography provides us with a broad space for creative use of light. Since there are so many advantages, we should really buy a special advantage that matches our camera next time. Please note that not all special strongpoint can complete all the functions mentioned above, so please read the manual carefully when purchasing to see if it is suitable for our camera. In fact, it doesn't matter if there is no special support point. Because most accessories are just for convenience, there is no need.