Where I can read something about the impulse interval characteristics?

[iosif_astrukov]

<p>Hi<br>

I am looking for some resources about the intervals of the impulse of the different lighting flashes and how is the connection with the voltage and the intensity?</p>

<p>For example - the intensity is formed with a long interval of impulse or the interval stays the same - but the lightning bulb flashes differently?</p>

<p>My question is provoked by this situation: <br>

When I was shooting a falling fruit in water, when I was shooting with single flash, it freezes perfectly even in 1/400 <br>

But when I used second flash /for the background/ the fruit was blurred and I had to sync at more than 1/2000 and still wash't ok every time<br>

In this case I used portable flashes - Nikon SB 900 & 700, and I don't know if it is a matter of how they sync - through the Nikon CLS, maybe they don't sync exactly on the same moment and I get kind of double exposure, or the problem is that the two flashes combine and I get longer interval of light… one of the flashes was on maximum power 1/1 <br>

So if somebody know a resource about how these things are connected I will be thankful :) I also don't know if there are major differences from the portable flashes and studio flashes - do they work on the same principles of controlling the power of the impulse?</p>

[ellis_vener_photography]

I think I know hat you are asking and if I am right...

 

It depends on the technology used for the flash, but for Speedlights like the type you are using and a very few more

powerful flashes (Einstein E640, Profoto B1, and high-end pack and head systems from Broncolor and Profoto) the flash

duration is controlled by an IGBT circuit. Intensity per millisecond is the same no matter the energy setting of the flash but

the duration of the impulse is curtailed to lower the total amount of energy released.

 

With aNikpb Speedlight at maximum power you are getting a longer flash duration than you would at a lower setting or

than you will if shooting in TTL controlled mode.

 

However since you mention that you are using shutterspeeds above the standard top sync speed of Nikon's DSLRs, the

Nikon flashes need to set to FP mode. In FP mode the Speedlights are sending a stream of very low power flashes timed

to cover the movement of the opening between the first and second shutter curtains. When you are not at A camera's

top sync shutter speed (1/200 or 1/250th) is the shortest interval that the entire are of the sensor is uncovered at one

time.

[iosif_astrukov]

<p>Thank you <a href="/photodb/user?user_id=17942">Ellis Vener</a> <br>

So… basically the power of the flashes is formed by the duration that it fires - longer duration = more power<br>

if I understood correctly… both for the portable flashes and the studio ones</p>

<p>Actually… I didn't know that when the shutter speed exceeds the top one - 1/200 - the flash is firing several times - right? </p>

[bebu_lamar]

<p>The power of the flash is both duration and intensity. They are different from flash to flash.</p>

[rodeo_joe1]

<p>The answer is simple. Stop using Auto FP. FP mode forces the flashes to emit a long series of flash pulses, which is the exact opposite effect to what you need to freeze movement.</p>

<p>Reduce the flash power and raise your ISO speed to compensate; stick to the standard X synch speed of the camera - probably 1/250th. I'd suggest you need to set both flashes to no higher than 1/4 power, and preferably lower.</p>

<p>There may also be an issue with CLS, which relies on the flashes "talking" to each other via a series of short flash pulses before the main flash. The slave flash then has to rely on an internal timing circuit to fire approximately at the same time as the commander. Not good for exact simultaneous firing of both flashes. For the setup you're describing, I'd ditch the use of CLS and buy a couple of P-C flash synch cables to couple the flashes to the camera and/or from flash to flash with a hardwire.</p>

[iosif_astrukov]

<p>Right, 10x :)</p>

<p>I found some writings on the subject and a nice video -

<p>I wanted to know the principles - how things work</p>

<p>For the specific setup I described - there are several options… the high ISO is not always the best one… I thought of an option to change the set - so that I could use less flash power - kind of 1/8… but still you need to set the sync speed to 1/200 as you are saying…<br>

but as the studio flashes have more power in a single short fire impulse - this is the easiest and best way to do it - in general<br>

thanks to all</p>