One interesting aspect of the X100 series design is that they have a leaf shutter that enables them to shoot at much higher flash sync speeds than cameras with focal plane shutters. This is an interesting feature as it enables a photographer to shoot at much wider apertures than normal in bright light, using a faster shutter speed to moderate the ambient light. Therefore it is possible to get that wide aperture, shallow depth of field image, while adding fill-flash, even in bright light. The camera also has an electronic shutter that works at up to 1/32000 sec in ambient light, but not with flash.
On most cameras, when using flash outside, we have to set our max sync speed of between 1/160-1/250th sec, lowest ISO and then set the aperture to get a 0EV (or just below) ambient exposure. Due to the limited shutter speed the aperture will normally have to be set at between f8-f11 to moderate ambient light, so there is very little creative control over depth of field and the flash has to work hard at those smaller apertures. The small aperture problem can be overcome by using high speed sync flash where available, but this uses even more flash power as the flash has to burn for a longer duration because the shutter curtains create a narrow slit for the flash to pass through as they travel over the sensor at higher shutter speeds.
On the X100T the leaf shutter enables flash sync at much higher speeds than 1/160-1/250. However, a slight complexity and limitation is that the shutter speed of a leaf shutter is not fixed but depends on aperture, presumably due to the time it takes for the shutter blades to travel the distance needed to make an exposure. At wider apertures they have further to travel. On the X100T the max shutter speed at f2 is 1/1000 sec, at f3.2 it increases to 1/1250, at f4 its 1/2000, at f7.1 its 1/2500 and at f8 and smaller its 1/4000. The good news is that the flash will sync at all those combinations of shutter speed and aperture, so even wide open at f2 the 1/1000 sec sync speed is at least 2 stops higher than most cameras. Being able to shoot at wide apertures even in bright light, makes the small, built-in flash more efficient because aperture is one factor that controls flash exposure and the bigger it is the less power will be needed. To help deal with the limitations in shutter speed at wider apertures for both ambient and flash exposures, the camera includes a built-in 3-stop ND filter that can be switched in and out. This helps to control ambient light further, when shutter speed alone is not enough to bring the exposure value down. Obviously the ND filter will affect the flash exposure too and the flash will then have to work harder.
So if you want to shoot at f2 you are ok as long as the shutter speed falls at or below 1/1000. If its above that you can pop in the ND filter to try to bring it within range. 3-stops should be enough for almost anything as 1/1000 with a 3-stop ND is equivalent in exposure value to the max shutter speed of 1/8000 sec in professional SLR cameras.
We had some snow today in southern England (a rarity indeed) and my little 4-year old (Theo) was desperate to get out and play, so we took him to a local hill to roll about and play on his sledge. I thought I would have a play with the high speed sync flash. Obviously, shooting a 4-year old who wants to play, not model, is not going to give the best artistic results, but the images certainly have a look to them that you cannot easily get with a normal flash setup in bright ambient light.
Here are a few. On some at least I was using the built-in ND filter as the ambient exposure exceeded 1/1000 sec. These were all shot using the built-in flash, which obviously has limited power but gives really good fill-flash. All jpeg files using Classic Chrome film simulation.
1/1000 sec @ f2
1/1250 @ f2.8
f2 @ 1/1000
1/1000 @ f2
Bearing in mind the small size of the X100T and its built-in flash and ND filter, you have quite a versatile little package to try flash shooting in a slightly different way that would normally require external ND filters and powerful flash guns. Its another way in which the X100T works well as an only camera or as something different for a shooter who already owns X-system cameras.