Riddle me this.

The model I set everything up for flaked, so me and Pat did some sync speed tests
(pat is my non-speaking very patient model)

I've included the settings, what am I taking a photo of, my mirror?
photos are portrait with the camera's top to the left.

135.0mm -- f/11.0 -- (1/250)sec -- ISO640
look at the left of the frame


faster shutter moved the line
155.0mm -- f/11.0 -- (1/320)sec -- ISO640


even faster shutter
155.0mm -- f/11.0 -- (1/400)sec -- ISO640



the lights were set on radio slaves
main camera right 3' above 6 feet from the model through an umberella
fill camera left even with and 4 feet from the model through an umbrella
hair snooted shooting from behind and above camera right.
not saying the setup is good, just what I was using.

here is one done "right"
155.0mm -- f/11.0 -- (1/125)sec -- ISO100


Pat is a great help... [grin]
 

OK, so I'm a little slow...  Are you teaching something, or asking for help?  Most (if not all) of today's DSLR's have a 'focal plane shutter'.  There are two curtains that travel in front of the film/sensor, one right behind the other.  They form a narrom slit of light that passes to the sensor from side to side, exposing the image from one side to the other.  The entire image is actually not exposed at the exact same time at fast shutter speeds.  The faster the shutter speed, the closer the curtains follow each other, therefore allowing less light onto any one area of the film plane at one time.  If I understand it correctly, the shutters actually move at a maximum rate, which is usually way slower than the shutter speed would infer.  If your camera sync's at 1/125 second, that is the fastest rate at which the curtains actually move.  Once you pass that speed, it is the distance between them that causes less light to reach the image sensor (effectively increasing the shutter speed).  Because of this, you will have a shadow from the second curtain being in the way of the light when the flash goes off once you pass the sync speed.  Much like an in-camera gobo that you probably didn't really want.  The faster your shutter, the more of the curtain is in the way to mess up your shot.  Hence the moving vertical shadow in your shot.  The light from most strobes is actually much faster than the shutter, so it's really only the camera's shutter type that restricts it.  Leaf shutters could sync at any speed because they actually formed an opening big enough to expose the entire film plane instantly at the shutter speed you set.  I believe that if you set your shutter fast enough with a strobe, you will actually get a shadow from both the first and second shutter, leaving just a thin strip of exposed image.  Might be fun to try while you are goofing around.

Anyway, if you were asking why, that's it.  If you were trying to teach something, hopefully I added a little to it.

Travis

They do.  I'm not sure of the answer to your question but my guess would be that the sensor cannot turn on and off as fast as the shutter speeds as the shutter moving across it. 

Now we just need to figure a way to "use" this to create something amazing... [grin]

You're right, Ed. It is amazing the fact that we can capture light and release it later. Then we can show copies of the captured light and discuss the results of this feat with people hundreds of miles away without speaking a single word. [grin]

My choice of words was flawed.

How can we use faster shutter speeds in the studio to create unique or artsy effects.

OK I confess, *stands up* My name is Bob Edens, and I'm a geek.

That's a good idea Travis. I think the best way to do the "moving" thing is with slow sync speed which is the same but controlled. the shutter opens first and the flash fires just before it closes freezing whatever. Great for bicycles. (your panning ability will matter a lot) [grin]

SOME MORE DATA FOR YOU-

M, F, FP, and X sync
Cameras designed for use with flash bulbs generally had one or more of M (medium) sync, F (fast) sync, or FP (focal plane) sync, designed for use with corresponding bulb types. These sync modes close the contacts a few milliseconds before the shutter is open, to put the main pulse of light at the best time relative to the shutter opening. FP sync was designed for use with FP (flat-peak) flash bulbs which were designed for use with focal-plane shutters. Most standard flash bulbs used M sync.

The Nikon F offered FP, M, and ME bulb synchronizations, in addition to the X sync.

X sync is a mode designed for use with electronic flash. In this mode, the timing of the contacts coincides exactly with the full opening of the shutter, since xenon flashes respond almost instantly.

Due to their construction, focal plane shutters as used on most SLRs will only allow xenon flash units to be used at shutter speeds slow enough that the entire shutter is open at once, typically at shutter speeds of 1/60 or slower, but some modern cameras may have an X-sync speed as high as 1/500. Electronic shutters used in some digital cameras do not have this limitation and may allow a very high X-sync speed.

Today, certain modern xenon flash units have the ability to produce a longer-duration flash to permit X-synchronization at shorter shutter speeds. Instead of delivering one burst of light, the units deliver several smaller bursts a time interval as short at 1/125 of a second. This allows light to be delivered to the entire area of the film or image sensor even though the shutter is never fully open at any moment. The downside is that the flash is of less effective intensity since the individual bursts are lower powered than the normal capability of the flash unit. Only certain camera and flash combinations support this feature, and the camera-flash pairings are almost exclusively from the same manufacturer, the first being the Olympus OM-4 with the F280 flashgun. Off-camera flash units with this feature are currently very rare.


 Rear-curtain sync
Some modern electronic cameras include the ability to fire the flash just before the closing of the shutter, so that moving object will show a streak where they came from and a sharp image where they were at the end of the exposure. This mode is called either rear-curtain sync or 2nd-curtain sync.


 History
The first camera to implement a flash synchronizer was the Exakta, in 1935.