I want to use it on my camera with up to 1/100 sec exposure. Flash duration (acording to some sources on net) is a few miliseconds or less. I think that even doubled power will fit in this 1/100 part of a second.
It is generally shorter exposures which are a problem when using a flash.
Assuming you're using a film with a focal plane shutter, the limit is the fastest speed at which the second curtain is released after the first curtain has fully opened.
A focal plane shutter works by having one (first) shutter which uncovers the film or sensor and another (second) shutter which covers it back up again.
At slow shutter speed (longer exposures) the first curtain opens, then the second curtain closes.
At fast shutter speed (shorter exposures) the second curtain is released while the first curtain still partially obscures the film/sensor. At very fast shutter speeds, the difference between the two shutters if very small, leading to a thin open slit moving across the film/sensor.
The fastest speed at which the entire film/sensor area is exposed all at once is the sync speed of the camera. This is the fastest shutter speed at which you can use a conventional flash.
Perversely, at faster shutter speeds, the flash duration needs to be longer.
For a typical flash, the peak intensity is a couple of ms. This is fine for any shutter speed from the sync speed and longer.
The sync speed is very close to the time it takes for a single curtain to traverse the focal plane aperture. Incidentally, it is also close to the actual time all exposures shorter than this take. As an example, a camera with a 1/90sec sync speed takes about 1/90sec to take a 1/1000sec exposure!
Because of this, shorter exposures require a longer flash duration (and also a very even level of illumination). With a 1/90sec sync speed, the flash needs to stay on for at least 12ms for a 1/1000sec exposure. Some modern flashes do this by pulsing the flash very quickly.
Even if you do this, then for the same flash power spread out over 10 times the duration with only 10% of the aperture open at any time, you only get 1/10th (not 1/100th) of the exposure.
A better solution to needing a faster shutter speed with a flash is to stop down or use a neutral density filter. Assuming the majority of the exposure comes from the flash, the flash itself determines the duration of the main exposure, not the shutter speed. You only need a shutter speed at or below the sync speed.
If you don't want to stop down (because you want a shallow depth of field) then the simple solution is to use a slower film speed (lower ISO) or an ND filter. Naturally, you may also need to make corresponding changes to flash power.
