Nikon CLS - 2 questions

Trevor Harris

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Jan 26, 2011
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Hello all,

I've got a few technical questions about the Nikon CLS. I've contacted Nikon, but with no response, so I'm posting here to see if anyone can help me out.

So my setup is a D200 with an SB-600 and I rented an SB-700 for this weeknd. I can control them both remotely, different groups and channels, yadda yadda yadda… I'm using my pop up flash as my master to control the both. I realize that the 700 can be master, and thus control the 600, but I'm not getting in to that at this point. My question is, if the signal to power both flashes is an IR-signal. IR is invisible to the naked eye, so why does the popup flash appear to illuminate?

Secondly, from what I understand, there is a pre flash that occurs (presumably after the ir signal is set) for TTL purposes. The second flash on all speedlights is the actual exposure based on metering from the first flash. So if both flashes are set to manual, then would this pre flash occur? When a photo is taken, there seems to be a dizzying array of flashes that occur, albeit it's pretty fast, but it could cause some to have their eyes closed in some photos.

That's all I have for now, but I'm sure I'll have more questions later. Thanking you in advance,

Signal to activate remotes is NOT IR it is a pre-flash from the pop-up

if your remotes are set to Manual you are not using TTL and exposure is set by how much light you set M on flash. If remotes are set to TTL then the preflash will tell camera how much light to flash. Make sense?
Yeah, I understand the manual bit, but what I don't understand is the need for a pre flash if everything is manual - the ammout of light required is already set.
The pre-flash is what triggers the OCFs.
So the pre-flash both triggers the other speed lights AND is used in calculating TTL exposure? In a single flash? I guess I thought these were two different events, for a total of 3. But if they're combined then there are only 2 events that occur...
The pop up flash has no way to generate the IR signal without also producing visible light.

IR is light, it's just light we humans cannot see.

Doing TTL flash is fraught with so many more problems and issues that just doing it all manually saves time and frustration.

An added benefit of doing flash manually is much more consistant results.
So the pre-flash both triggers the other speed lights AND is used in calculating TTL exposure? In a single flash? I guess I thought these were two different events, for a total of 3. But if they're combined then there are only 2 events that occur...

There actually are more events that happen, The pop-up fires it's preflash, that tells the other groups to fire their preflashes in order of groups and set exposurse and then a flash is fired that fires all the flashes at the TTL power.

If you want to prevent blinking, use the FV-L button to fire all the pre-flahses and lock flash exposure, then wait a second and hit the shutter button and no more preflashes, just flash
I use the same setup- SB-600 and SB-700...

So, with TTL the pre-flash that you are seeing is your camera sending out light to see the reflective properties of the scene, then analyzes it, and sends a what it deems as the appropriate settings to you remote flashes. This is the CLS in action.

When you switch it over to Manual, your preflash now goes away as you are not letting the flash/camera do the creativity part, the task and settings are on you.

For Master- When you switch over the SB-700 to master it gets placed on your hotshoe and will allow you to control in groups and channels, other remote flashes like your SB-600.
This is handy for a body that does not have commander mode, or if you plan on have your on camera bounced and additional lights on your subject. Example group shot of 25 with two strobes in umbrellas at 45's at the edge of the ground and your on camera flash bounced in the center.
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Cool, thanks guys for all the replies! I think I'll make the decision to just go manually from now on, it just seems like the next stage in gaining enough experience. Thanks again!
Wireless CLS works in the following way.

1. User Presses shutter
2. Onboard flash fires out data bursts to signal all TTL flashes to prep TTL bursts, and all AA flashes to prep AA bursts.
3. External flashes (not configured as manual) fire a test shot.
4. Camera calculates required exposures of each flash.
5. Onboard flash fires out data bursts to give all flashes except those set to AA their final firing level.
6. Onboard flash fires sync shot to trigger remote flashes.
7. Shutter opens.
8. Remote flashes fire.
9. Shutter closes.

Depending on your settings there's variants of that. You'll notice your preflash shots have varied duration, i.e. if you have 3 groups set to wireless TTL then the preflash scenario takes ages and often will cause your models to blink. If your remotes only fire in manual then the preflash scenario is very short as there's no metering to be done and the entire thing is over very quickly. If your remotes are set to SU-4, and your onboard flash is set to 1/128th then the shutter is effectively instant as there's no wireless communication to do either.

All if this is done in IR, but the number one source of bright IR available on your camera is through the onboard flash, that's why it fires even if it's set not to in the wireless command menu. The critical thing is that the flash fires BEFORE the shutter opens so contributes next to nothing to the final image.

On really reflective surfaces such as mirrors you can see the reflection of your onboard flash. If this is a problem go hunt down an exposed film leader (the black part of the film that comes back with your negatives) and tape it over the front of your flash. This is transparent for IR light and thus will let the wireless CLS work without contributing anything to the final image.
well geez Garbz, blow everyone outta the water why don't 'cha. Thanks so much for the response, exactly the explanation I was looking for!

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