Flash not firing during live view

Question

Canon camera (6DII in my case) won't fire flash in live view mode (normal works fine) also not when using the canon connect app. I saw answers saying 'Disable silent LV shooting in the menu. There is "silent lv" 1 and 2. Just disable it and it will work' This is indeed the solution but dont forget to add youhave to have live view active when opening the menu to see the option. In the 6DII a 5th option only appears in the camera settings when live view is on otherwise it's no use looking for the silent LV mode. Just to let yall know this

Answer 1

You might want to know why flash doesn't work with silent shooting.

The 6D Mark II uses two shutter methods: 1) a mechanical shutter that reveals and subsequently obscures the sensor using two shutter curtains transiting across the sensor and 2) a first curtain electronic shutter. The former is used with shooting while using the optical viewfinder (also with Silent Shooting set to Disable when using Live View). The latter is used when using Live View with one of the Silent Shooting modes enabled.

The mechanical shutter is fairly fast. It's fast enough that at 1/180 seconds exposure time (5.55 milliseconds), the 6D Mark II's entire sensor is revealed at the same time for a fraction of the total exposure time. This is the instant, while the sensor is completely uncovered, when the camera tells the flash to fire. It stays fully uncovered for only around 1-2 milliseconds, which is just long enough for most portable speedlights to discharge their energy in a flash of light.

Before the exposure begins the first curtain is closed, covering the sensor, and the second curtain is open, stored above the sensor. The first curtain opens by moving towards the bottom of the sensor, away from where the second curtain is stored, to progressively reveal the sensor from top to bottom, which is from bottom to top of the inverted image projected by the lens. Then the second curtain closes by moving from the top of the sensor, in the same direction as the now-stored first curtain moved before being stored at the bottom of the sensor, to cover it back up. Both curtains move across the sensor in the same direction, one after the other. The total exposure time for any given point on the sensor is the time difference between when the first curtain uncovered that point and when the second curtain covered it.

At exposure times shorter than the 6D Mark II's flash-sync speed of 1/180 seconds the first curtain is still in the process of opening to reveal the sensor as the second curtain begins chasing it to cover the sensor back up. The entire sensor isn't fully revealed at any single instant during any point in the sequence for exposure times 1/200 and shorter. In other words, for exposure times shorter than 1/180 the sensor is exposed by a slit between the first and second curtains as they move across the face of the sensor. The curtains move at the same speed across the face of the sensor, regardless of the selected exposure time. The narrower the slit between them is, the shorter the exposure time is. This is because each spot on the sensor is uncovered for a shorter duration as the slit between the two curtains passes over it than the total time it takes for the curtains to travel all the way across the sensor. For exposures longer than flash sync (X-sync), the total exposure time includes additional delay between when the first curtain fully opens and when the second curtain begins to close.

_{This video is time stretched by a factor of 400X. You can see the full sequence, beginning with the movement of the mirrors, on YouTube. Notice in the full sequence that the shutter curtains wait to begin moving back to their starting position until the mirror is almost fully back down. This allows time to read out the sensor before moving the shutter curtains back up. The camera in the video is a Canon 7D, but other mechanical shutters from Canon, as well as from other camera makers, are similar.}

However, the mechanical shutter is not silent. The first curtain makes noise as it opens. The second curtain makes noise as it closes. Then both make noise as they are reset to their starting positions. Keep in mind that the majority of the noise one hears when using a DSLR with the optical viewfinder is due to the movement of the mirror, not the shutter curtains. But the shutter curtains also contribute some noise which can be heard when using Live View and the mirror stays locked up. Even when Silent Shooting is set to Disable and both curtains move in a more normal sequence, it's still a lot quieter than when the mirror also flips up and down.

In order to shoot fully silently, the only possibility is replicating the shutter electronically. The trouble is, electronics can't cover the sensor. Electronics can ground the photosites, so that they can't accumulate any charge, but that destroys whatever charge there was at the photosite. So the first curtain is easy, just gradually un-ground the photosites progressively from the bottom to the top of the sensor. You can do that as fast or as slow as you want.

There are only two possibilities that allow the second curtain to be implemented and neither is totally satisfactory. One possibility is that the sensor has half of its area as light-collecting pixels and half of its area as memory pixels that are shielded from light. Then quickly move the charge from light-collecting pixels to memory pixels all at once when doing the electronic second curtain. The trouble is, this halves the light-collecting area and thus the sensitivity of the sensor. Because it requires twice as many pixels (half of them don't collect light), it's also very expensive. So that's why practically no camera is doing this.

The other possibility is to just read the pixels gradually. Because reading the pixels is slow, the electronic second curtain moves slowly. To match that to get even exposure, the electronic first curtain (gradually release the grounding of the pixels) also has to be artificially moved very slowly. This slow speed means the sensor is usually completely collecting light only at 1/30 seconds shutter speed or so. So while theoretically the camera manufacturer could allow using flash with silent shooting at 1/30 or slower shutter speed, they usually prevent that as those are too slow shutter speeds for most uses.

So what many cameras, such as Canon's 6D Mark II, do is they use electronic first curtain to begin exposure, then use one of the mechanical curtains to end exposure. Though not totally silent, it is considerably less noisy than the fully mechanical shutter, which moves two curtains in quick succession across the sensor and then moves both of them back to their starting position after the sensor is read out. Instead, when using one of the Silent Shooting modes the exposure starts with both curtains open, one stored on either side of the sensor. The sensor is switched on progressively from the bottom to the top of the sensor to begin exposure. The rate of this progression is timed to match the rate at which the camera's mechanical curtains cross the sensor. To end the image only one of the mechanical shutter curtains need to move to cover the sensor. Once the sensor has been read, only that one curtain needs to move again to reopen so the sensor can provide a Live View image for composing the next shot. With some silent shooting modes, the reopening movement of the curtain can be delayed as long as the shutter button is held fully pressed and only reopens once once the shutter button is released. This can be useful for situations when delaying the noise of the shutter's second movement is desired, such as during a tennis serve or golf swing. With at least some of Canon's DSLRs, such as the 7D and 5D Mark III, which curtain closes to end the shot depends on whether you've selected Silent Shooting Mode 1 or Mode 2. With more recent Canon DSLRs, such as the 7D Mark II and 5D Mark IV, the first curtain moves from the bottom of the sensor to end the exposure in both Silent Shooting modes.

Newer mirrorless cameras such as the Canon EOS R3 appear to be making progress in the flash sync speed of silent shooting. How they do that is that they have managed to improve the sensor reading speed. By improving it, the electronic second curtain moves much quicker. You can then move the electronic first curtain quicker too, to match the increased speed of the electronic second curtain.