[StarDust]

For statement #3, I think it would be more clear when one realizes that a flash photo at x-sync speed is really a double exposures. One exposure at x-sync speed using the ambient light to light up the subject and another separate exposure from the flash at the duration of the flash. These two exposures are combined into a single photo inside the camera. If the subject is moving so fast that one could see motion blur when shot at 1/180 shutter speed without flash, then one would also see this motion blur when the same scene is shot using the same setting (1/180 shutter speed) with the flash.

What you mean to say or what's really happening is that there is only a single exposure, but during the exposure time you have two moments of different luminances.


Now what frustrates me is that the camera has no override for sync speed since the flash fires at a fraction of a second, firing at 1/4 power and at 1/250 s might just be enough to light up the scene, but I guess it has to do with that only a slit is sliding over the sensor at speeds faster than 1/180 s and in that case it would only light up a part of the frame.
I just had an epiphany, I think. The reason that the flash has to fire several times has to do with the fact that it lights up several parts of the frame to make the whole frame lit up.
Is this correct? In that case I'll just have to wait till Pentax shortens the X-Sync speed on their cameras.

[enoeske]

What you mean to say or what's really happening is that there is only a single exposure, but during the exposure time you have two moments of different luminances.


Now what frustrates me is that the camera has no override for sync speed since the flash fires at a fraction of a second, firing at 1/4 power and at 1/250 s might just be enough to light up the scene, but I guess it has to do with that only a slit is sliding over the sensor at speeds faster than 1/180 s and in that case it would only light up a part of the frame.
I just had an epiphany, I think. The reason that the flash has to fire several times has to do with the fact that it lights up several parts of the frame to make the whole frame lit up.
Is this correct? In that case I'll just have to wait till Pentax shortens the X-Sync speed on their cameras.

At below the sync speed, 1/180, the entire sensor is exposed at once and requires only 1 burst from a flash. Above that, faster than 1/180, the sensor starts becoming a moving slit and only exposes parts of the sensor at a time. This is when you need HSS. It makes the flash shoot off repeatedly to match the moving slit over the sensor.

If you are just into HSS territory, say 1/350 shutter speed, then the pulses from the flash are relatively slow and will not "freeze" motion. Getting up to 1/2000, however, the pulses are very short and will freeze almost any motion.

[ma318]

What you mean to say or what's really happening is that there is only a single exposure, but during the exposure time you have two moments of different luminances.

I think it is basically semantics. We are probably trying to describe the same thing but in a different way. For me, it is easier to "think" of it as a double exposures. When I think that way, then it becomes clear why one needs to control both exposures, flash exposure and ambient exposure, when you are shooting in manual mode (camera and flash).
Strictly speaking, if you define a double exposures as a combined exposures with the shutter opening and closing twice, then I guess it is not a "double exposure".
Please see this.
Four Flash Photography Basics we must know

Now what frustrates me is that the camera has no override for sync speed since the flash fires at a fraction of a second, firing at 1/4 power and at 1/250 s might just be enough to light up the scene, but I guess it has to do with that only a slit is sliding over the sensor at speeds faster than 1/180 s and in that case it would only light up a part of the frame.
I just had an epiphany, I think. The reason that the flash has to fire several times has to do with the fact that it lights up several parts of the frame to make the whole frame lit up.
Is this correct? In that case I'll just have to wait till Pentax shortens the X-Sync speed on their cameras.

With HSS, the flash actually flashes thousands of times a second. For all intend and purpose, one should think of the "HSS flash" as a continuous stream of light that lasts for the duration of the shutter speed.
See this link.
Flash Photography 101, Chapter 4 - Guide Numbers and High Speed Sync - Canon Digital Photography Forums

I am looking forward to the day when DSLR makers can get rid of the mechanical shutter and replace it with an electronic one. When that happens, the x-sync speed will only be limited by the flash duration. Rumor is circulating that Panasonic is going to offer this with their new micro-four thirds camera soon. Apparently it is easier to implement an electronic shutter without compromising IQ on a smaller sensor.
Panasonic GH2 to be first shutter-less camera - Blogs - EOSHD.com

And all Point and Shoot cameras already use electronic shutters. P&S cameras like the G11 are great if you want very high x-sync speed. G11 has 1/2000 sec x-sync speed.

[ma318]

Getting up to 1/2000, however, the pulses are very short and will freeze almost any motion.

Unfortunately the fast motion could be distorted when using HSS.

High Speed Shutter vs. Ordinary Flash Sync

[StarDust]

I am looking forward to the day when DSLR makers can get rid of the mechanical shutter and replace it with an electronic one.

But then it's not an SLR anymore, it's more SLE or something.

[ma318]

But then it's not an SLR anymore, it's more SLE or something.

Not really! With an electronic shutter, it could still be called an SLR. SLR stands for "single lens reflex". It describes the lens/mirror/prism combination to allow for a true thru-the-lens viewfinder. It does not require the shutter to be mechanical or electronic. In fact, the Nikon D40 and D70 already used a combination of mechanical and electronic shutter to get 1/500 x-sync speed and we still call them SLR.

Single-lens reflex camera - Wikipedia, the free encyclopedia

d40x and flash sync speed - Photo.net Nikon Forum