It is said that the flash will flash in ettl metering mode, but I didn't notice the flash. Why?

The main purposes of pre-flash under ettl are: white balance test; At the same time, exposure test can eliminate red eye in a specific shutter speed range.

Triggered when the shutter release button is pressed, and ended when the front curtain of the shutter is opened. From the opening of the front curtain to the closing of Hou Lian, the official flash trigger is usually short, but it can still be felt. If you want to experience its two flashes, you can slow down the camera exposure time (M file) by more than 11second, or even slower than1second, and then set the flash to Hou Lian flash, and you will see the pre-flash and the official flash clearly.

In addition, when the shutter speed is above 1/60S, pre-flashing can't prevent red eye. At this time, the red-eye prevention depends on the auxiliary focusing light emitted by the flash (Canon is red, Nikon seems to be white), but it will not be completely eliminated. To eliminate red eye, we need to slow down the shutter speed again, but not too slowly, because it is too slow, people's pupils will return to their original state after contraction, and red eye still cannot be eliminated.

The built-in flash you mentioned does have the function of preventing red eye. Unlike external light with infrared auxiliary focusing light, it takes several strobes to narrow the pupil of the subject and test the white balance and exposure.

Even if red-eye protection is turned off, white balance and exposure will be tested. cq_3966