Using Flash

[TC]

What is the speed of a flash compare to the shutter speed? Is there a setting in flash for slow speed? or is the speed of the flash always constant and the variable is the distance and intensity?

[phillipb]

What is the speed of a flash compare to the shutter speed?

You can easily get 1/50000 sec.

is the speed of the flash always constant and the variable is the distance and intensity?

Correct.

[ATJ]

Most electronic flashes have a duration of around 1/1000s when on "full power'. The power settings work by changing the duration. The duration of the flash is certainly not constant, unless you are using manual and then it is only constant if you don't change the "power". The intensity is actually constant (within reason given a very short duration may not result in a full flash).

TTL works by decreasing the duration of the flash. In the traditional film based TTL, there was a sensor in the camera that took a reading off the film itself. When you took a photo, the sensor would read the amount of light being reflected. Once enough had been received, it would turn the flash off. Thus, the "power" was really the duration of the flash. With digital TTL, the preflashes determine the required duration and then the main flash is lit for that duration.

[phillipb]

Andrew, I may stand corrected as far as the "constant" part is concerned, specially with modern flash guns but I'm pretty sure that the speed can be much faster then 1/1000 sec. just a quick google came up with this

Flash and Camera Shutter Speed

Flash exposure is not affected by the camera shutter speed. This is because electronic flash lasts for about 1/10,000 seconds, faster than shutter speeds used for daily photography.

Whether the camera's shutter speed is 1/30 or 1/125 seconds, the amount of light from the flash reaching the camera's image sensor will be the same.

from this website http://digital-photography.suite101.com ... ndamentals

[gstark]

Andrew, I may stand corrected as far as the "constant" part is concerned, specially with modern flash guns but I'm pretty sure that the speed can be much faster then 1/1000 sec. just a quick google came up with this

Flash and Camera Shutter Speed

Flash exposure is not affected by the camera shutter speed. This is because electronic flash lasts for about 1/10,000 seconds, faster than shutter speeds used for daily photography.

Whether the camera's shutter speed is 1/30 or 1/125 seconds, the amount of light from the flash reaching the camera's image sensor will be the same.

from this website http://digital-photography.suite101.com ... ndamentals

To state that flash exposure is not affected by the camera shutter speed is largely correct.

Largely. For the following discussion I'm going to pretend that high speed fp flash and electronic shutters do not exist. We can come back to discuss them later.

As a general rule, the selected shutter speed always needs to be one that is specified as being x-synchronised. If this is not the case, then you run the risk of having the flash go off either before the shutter is fully open, or after it has started to close. The deal is that the shutter must be fully open when the flash goes off.

Many cameras today have a sync speed of 1/200 or thereabouts. Basically, that specified shutter speed, or any slower one, is suitable for use with flash.

That may lead to some other exposure-related issues. Consider that you're shooting outdoors, and your camera's sync speed is 1/200. You decide that you're going to shoot f/16 @ 1/60, which, according to sunny 16, is the correct EV setting.

What's the deal here: what do you need to do? Do you know how to address this situation?

[ATJ]

Andrew, I may stand corrected as far as the "constant" part is concerned, specially with modern flash guns but I'm pretty sure that the speed can be much faster then 1/1000 sec.

Yes. The speed CAN be much faster than 1/1000s. As I said, if you use less than "full power" the duration will be less. i.e. the speed will be faster.

Do you have an SB-800? If so, look at page 122 of the manual. Tell you what, I'll save you the trouble:

1/1050 sec. at M1/1 (full) output
1/1100 sec. at M1/2 output
1/2700 sec. at M1/4 output
1/5900 sec. at M1/8 output
1/10900 sec. at M1/16 output
1/17800 sec. at M1/32 output
1/32300 sec. at M1/64 output
1/41600 sec. at M1/128 output

[TC]

oh dear..seems to have ask a few very technical questions..

this is a panning shot @1/200s in good light, there's lots of "speed" in it.



this is a night shot @1/80s with flash and its a "freeze shot"


how do I take a panning shot with a sense of "speed" at night with flash?

[ATJ]

how do I take a panning shot with a sense of "speed" at night with flash?

Is there any ambient light at all or is it dark? If there is some ambient light, you can use rear curtain flash and a long shutter speed. With rear curtain flash, the flash goes off at the end of the time that the shutter is open. You get some exposure from the ambient light and then the flash goes off and freezes the action. The ambient light gives you the motion blur. You'd have to experiment a bit to get it working but it can work quite well.

[TC]

ATJ, thanks for that..more experimenting