How much time between the iTTL preflash and actual flash?

[Chan Tran]

I tried to determine the time between the preflash and the actual exposure flash of the Nikon SB-800 but I can't. I use the Minolta Booster II sensor connected to an oscilloscope but I could only see the actual exposure flash but not the preflash.

 

[ic-racer]

Are you using an F6?

I believe that is the only camera they ever made that can use the system.

According to my F6 manual, the flash should emit a 'series of pre flashes." I don't have an i-TTL compatible flash to see this myself.

 

[koraks]

I tried to determine the time between the preflash and the actual exposure flash of the Nikon SB-800 but I can't. I use the Minolta Booster II sensor connected to an oscilloscope but I could only see the actual exposure flash but not the preflash.

Isn't the point of TTL (and its derivatives) that the flash is turned off as the desired level of exposure is reached, as measured Through The Lens during exposure? If memory serves, that's how it was done initially and if it worked back then (mid-1980s, e.g. Canon T90), I guess they stuck with it?

Pre-flashes - aren't those just used for red-eye reduction?

I know Canon does have a high-speed sync mode on their flashes, but that employs repeated high-speed strobing to hit a sort of accidental sync between the exposure and one of the brief flashes.

 

[Chan Tran]

Isn't the point of TTL (and its derivatives) that the flash is turned off as the desired level of exposure is reached, as measured Through The Lens during exposure? If memory serves, that's how it was done initially and if it worked back then (mid-1980s, e.g. Canon T90), I guess they stuck with it?

Pre-flashes - aren't those just used for red-eye reduction?

I know Canon does have a high-speed sync mode on their flashes, but that employs repeated high-speed strobing to hit a sort of accidental sync between the exposure and one of the brief flashes.

That is with film camera. Digital camera can't do off the sensor flash measurement so they have to do a weak preflash and use the sensor in the viewfinder to measure the flash then set the power for the main exposure.

 

[Chan Tran]

Are you using an F6?

I believe that is the only camera they ever made that can use the system.

According to my F6 manual, the flash should emit a 'series of pre flashes." I don't have an i-TTL compatible flash to see this myself.

Is this strictly film? I think I may have posted in the wrong area. I meant for digital camera.

 

[koraks]

Alright, I didn't realize we were talking about digital specifically.
I've moved your thread to a digital hybrid space to prevent confusion; thanks for clarifying.

 

[ic-racer]

Maybe someone with an F6 will chime in here. I only have SB-28, so I'm curious about how this works on F6.

 

[Chan Tran]

I found the answer. I was able to measure the delay. It's 67mS. Initially I set the scope to a fast sweep rate and thus only catch one of the light burst and not both.

 

[koraks]

That's surprisingly long; you can actually see the two flashes as distinct ones.