high speed flash

[bryanx99]

i'm still kinda new to photography, so this will probably be a stupid question. i use a rebel xti and currently have sigma 28-70 mm and a 70-300mm lenses. i'm really into high speed photography, and want to be able to use the highest shutter speed i can, but the flash won't fire past 1/200. if i buy an external flash, will it go higher?

[mdwsta4]

these may help
http://www.diyphotography.net/universal_sound_and_optical_slave_flash_trigger

http://www.diyphotography.net/diy_high_speed_photography_at_home\

[demonsmercy]

I am using the same camera as you. and I am new too. In fact, you can use as high as you want in shutter speed if you have an external flash.

[mdwsta4]

that's not true. check your flash's manual. typically the fastest sync speed is around 1/125-1/250 of a second (some flashes have a high speed mode so check for that too). if you shoot with a shutter speed faster than what your camera/flash can do, you will see a black bar on the bottom part of your photo because the light was not able to illuminate the subject fast enough.

I am using the same camera as you. and I am new too. In fact, you can use as high as you want in shutter speed if you have an external flash.

[sdjl]

You may want to look at increasing your ISO setting in order to get faster shutter speeds. This will have a side effect of making the photo slightly grainy the higher the ISO is, but will help in getting faster shutter speeds.

[Tiberius]

Okay, here's a bit of background on the subject of why shutter speeds are limited when you are using flash.

The shutter inside the camera is actually made up of curtains. The type you get at the theatre that go up and down, not the type you get at home that go side to side. And there are actually two curtains. When the camera isn't taking a photo, the first curtain is positioned in front of the sensor (or film) blocking light from reaching it, and the second curtain is positioned above and out of the way.

When you take a photo, the first curtain drops down out of the way. This lets the light through to the sensor/film. Then, after the exposure is over, the second curtain drops down to block the light again. Then, both curtains slide back up to reset the mechanism, ready to take another photo.

However, when you use faster shutter speeds, the second curtain starts dropping down before the first curtain has reached the bottom. Because of this, it means that the entire sensor/film area is never being exposed all at once. At these speeds, only a strip of the frame is being exposed at any one time.

Normally this doesn't cause problems, because ambient light is constant and won't change during the exposure. However, because the burst of light from a flash unit is so incredibly quick, it doesn't last long enough for the slit between the two curtains to move over the entire frame. if you took a photo like this, the frame would be dark with only a thin strip of picture - the strip being where the slit between the two curtains was when the flash went off. This is obviously not a good idea for a good photo! :P

The way around this is to limit the shutter speed to one that lets the entire frame be exposed when the flash goes off. This is why the camera won't let you set a speed above 1/200, or 1/250. The actual speed varies depending on the camera.

However, if you have certain models of external flash, there is a way to get around this limitation. Some flash units can let you put them into FP flash mode. All you'll really see in this mode is that you can set your shutter speed to anything the camera is capable of, and you'll lose a little of your flash range.

But there's more going on that you don't see. :P The flash doesn't actually fire once, it fires several times. This is how it avoids having the thin strip of light across the picture. But since the flash is firing several times, it can't fire at full power - it could never recharge in time to flash so quickly if it did. This results in a loss of flash range.

The main idea for this is so that if you are taking a portrait on a bright sunny day, you might want a wide open aperture to limit your depth of field. This would require you to have a fast shutter speed to avoid over exposure. normally not a problem, but if you want to add a bit of fill flash to reduce the shadows, then you'd be in trouble, because the flash won't work with a fast shutter speed. FP flash mode lets you get around this.

However, if you are planning on taking photos of high-speed things, you might find it easier to simply do it in the dark. if there is zero ambient light, then the photo will only show what happens when the flash goes off. It won't make any difference if the shutter speed is 1/200 or 10 seconds. Since the burst of light from the flash is so brief, and there is no ambient light, the only light will be from the flash, giving an effective shutter speed of the time the flash was actually lit for - generally about 1/10,000 of a second, if I recall correctly.

However, an external flash unit is a good buy for many other reasons. You can use it for bounce flash, and if you get an optical slave you can mount the flash off camera and give your photos much more depth (although with Canon's E-TTL flash metering it gets a little tricky).

As a starting point, the Canon 580EX will let you use the FP flash mode. However, it is also insanely expensive. Bear in mind, however, that the 580EX will do just about everything you could ever want a flash to do. For more information, take a look at the FP Flash section in the EOS flash article on Photonotes.org. You can find it by clicking HERE (http://photonotes.org/articles/eos-flash/#fp).

[mdwsta4]

here's another article you may find helpful
http://strobist.blogspot.com/2007/06/hacking-your-cameras-sync-speed-pt-2.html

published today

[Jargon]

Wow! That's a nice long explanation, Tiberius! Yes, I read the whole thing. :)

[bryanx99]

thanks for the help, guys. gonna try to find a friend who can make me that slave flash, since i know almost nothing about electroincs work. i'd probably accidentaly make a robot that would take over the world or something.

[matthewchj]

The other option would be to take the photo in a dark room with a long shutter speed and having a separate flash firing. Since the room is dark, there will be no exposure until the flash is fired, therefore the duration of the exposure would actually be the duration of the flash firing. Since the burst of light from the flash is very, very short compared to the shutter speed that the camera can normally use when using flash, the effective shutter speeds can go very low.