need some help with shutter priority mode with flash on

[parkkibum]

I was bored at home and decided to take water drop shots.
i realized that with flash on 1/200 is my fastest speed with shutter or manual mode,
without flash i can take faster shot but it's too dark even if with maximum aperture unless i have extra lights available
with flash i can take decent shot but i dont think 1/200 is fast enough to capture water shot. any advice? i used 18-55 bundle lens.
i just want to make sure 1/200 is fasfest speed with flash on, hope nothing's wrong with my camera.

[OsmosisStudios]

Your camera has what we call a flash sync speed. What it means is that that is the speed at which the sensor can be exposed completely to the flash of light. If you were able to shoot faster than 1/200 with the flash, you'd end up wit hhalf an image properly exposed and half would be black. Luckily, your camera has this figured out and doesnt let you do it.

Iunless youre using the larger flashes (like the 580exii) you're stuck. You can use the High Speed Sync mode, but that'll be up to someone far more capable than I to explain.

[inkista]

What camera are we talking about?

[parkkibum]

i use canon xsi

[inkista]

Ok. Here's what's going on.

The shutter speed on your camera is determined by the gap between the two shutter curtains. That gap travels over the sensor during the exposure. The faster your shutter speed, the smaller the gap becomes. If your shutter speed is faster than 1/200s, that gap becomes smaller than your sensor.

A flash burst is much faster than your top shutter speed. So, when the shutter curtains block off parts of the sensor, only the uncovered parts will see the flash burst. The result is that you get black bars across the frame (usually at the top and/or bottom). So, that's why the camera is limiting you to 1/200s--so the whole frame will be illuminated.

High-speed synch is a technology where the camera and the flash communicate, and the flash sends out pulses, timed with the gap sweeping across the sensor, so the whole frame is illuminated. BUT--this will only work with an external flash unit. There is no way to set high speed sync with the built-in pop-up flash (at least, not according to the XSi menus described on dpreview).

So, again, this is why your camera is limiting you to 1/200s in Tv mode.

Secondly, when you're in Av or Tv shooting modes, the camera is assuming that you just want the flash for fill, to lift the shadows, and that the main illumination in the scene is going to come from the ambient light. In Tv mode, that means you'll get the shutter speed you set (up to 1/200s), but the aperture will be set very close to what it would be with no flash at all, and vice versa for Av.

I highly recommend reading through the EOS Flash Confusion section of the "EOS Flash Bible".

Basically, you have to figure out how you want to balance the flash against the ambient and then control it. And Manual mode is going to be the best way to do that.

If that's too much thinking for you, and you just want the subject to be lit and who cares about the background, then just shoot in P mode.

[parkkibum]

thanks a lot guys I've read through manual and it was exactly what you guys said
I guess I should keep reading the instruction manual until I master it!