Extremely urgent! Why is the shutter speed of SLR camera set to the maximum flash synchronization speed?

Nowadays, many photographers use digital single-lens reflex cameras, such as Nikon D 100, Nikon D70 and Canon 300D. These cameras have synchronous shutter speed when using flash, which is an important part of curtain shutter cameras with flash. The so-called synchronization speed is the shortest time required for the camera to completely open the shutter blade, so that all areas of the subject can be evenly illuminated by the flash. Generally, the synchronization speed of high-end digital cameras is 1/250 seconds, and that of ordinary cameras is1125 seconds or1180 seconds.

For most beginners, the synchronization speed of flash is a relatively uncommon concept, which seems to have no direct connection with taking pictures. Actually, it is not. If the photographer chooses the shutter with higher synchronization speed when using the flash, some pictures will be blocked by the shutter page and cannot be illuminated by the flash. It can be seen that mastering the synchronous speed of the flash is a compulsory course for taking pictures when using the flash. Here we summarize five basic principles for making good use of flash synchronization speed.

1. When using the flash, you can't use the shutter speed higher than the synchronized file.

In general, the shutter speed can be lower than the synchronization speed when using the flash, but not higher than the synchronization speed. Generally, portable digital cameras and digital cameras similar to SLR use inter-mirror shutters, so that each shutter can be synchronized with the flash when exposed, so photos taken at any speed can be exposed evenly, so there is no flash synchronization speed, that is, all shutters from the highest shutter speed to the lowest shutter speed are synchronized with the flash.

2. The special flash will automatically control the shutter speed.

The information about shutter speed and aperture and whether the exposure is sufficient between the camera and the flash is communicated with each other through several pairs of contacts between the hot shoes and the flash. Therefore, in order to prevent mistakes, the flash will actively control the shutter speed according to the actual situation. If the speed gear used in camera mode is higher than the synchronization gear, the flash will automatically make the camera shutter speed lower than the synchronization gear. For example, if you shoot with cameras "P", "A" and "S" and use a special flash, the flash will automatically select the synchronization speed or the shutter speed slightly lower than the synchronization speed. For example, when Nikon D 100 camera and SB800 electronic flash are used together, the camera shutter speed is automatically set to 1/60 seconds.

3. You can choose the shutter speed by "m".

In photography practice, if the photographer has his own requirements for exposure, he should choose the shutter speed flexibly according to the actual situation and his own needs, and he can choose any shutter speed slower than the synchronous speed. The advantage of using low-speed shutter is to make full use of natural light and reduce flash marks. But when using the "P" file, the photographer can't change the shutter speed, so he should use the "M" file to shoot, so the shutter speed can be changed at will.

4. The influence of low-speed shutter on exposure.

Because the subjects in life are all three-dimensional or have a certain sense of depth, in many cases, there is a certain distance between the subject and the background, and the flash is affected by the illumination inverse square law, which leads to the Gao Fancha phenomenon that the close-up subject is exposed accurately and the background is darkened due to insufficient illumination. If you need to adjust the contrast, you can use a low-speed shutter, such as 1/2s,1sec or even the "b" gate for long-time exposure shooting. By combining the low-speed shutter with an appropriate aperture, the background can be exposed more and the contrast can be reduced to some extent. The method of reducing shutter speed is more suitable for shooting black and white film. When dealing with color film, if the color temperature difference between natural light and flash is large, there may be a situation that the color temperature of the subject is inconsistent with the background.

5. Measures taken to reduce the influence of on-site light.

Contrary to the above requirements, in order to use the brightness of light to purify the background and highlight the subject in some messy occasions, it is necessary to adopt the shutter speed as high as possible in some specific shooting occasions, such as the highest synchronization speed of 1/250 seconds. The advantage of choosing a high-speed shutter is that it can reduce the influence of natural light on exposure, and objects that are not irradiated by the flash will be hidden in dark tones, which is more than when normal color temperature is needed to restore or highlight the content of the object irradiated by the flash.

In addition, when shooting at night, if the brightness of the environment is very low, you can also use a camera with slow synchronization speed for so-called "high-speed photography" to "condense" some high-speed moving objects on the photo. The reason is that, for example, when shooting at shutter speed 1/60s, there won't be too many traces on the negative due to the low brightness of the background environment, and the brightness of the negative is mainly provided by the flash. If the flash duration of the flash used is110000 seconds, the actual effect is equivalent to using 1/65438+. Such a high shutter speed can naturally "condense" the images of some high-speed moving objects on the negative. We have many photos taken by flash at night that are clearer than those taken during the day (assuming exposure at the same shutter speed), which is the reason.

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