muti flash TTL w/ cords on a dslr???

[chris_burville]

Hello all,

 

I have been awestruck at the apparant inability to get TTL with 2 sb-800's and a D200/300 using cables

instead of wireless. I shoot a lot of action wildlife, especially birds, and want to get creative using multiple

flashes & motion blur etc. in dynamic, often hand held, situations.

 

I will generally want to place the flashes where the wireless sensors cannot 'see' each other (such as on

either side of a big tele lens). That and the shutter lag from the pre-flashes all but renders the CLS system

inoperable in fast action situations. I bought an sc-29 ttl cord for one strobe off camera and an sc-27 ttl

cord to connect the 2 strobes. Then i find out that the sc-27 only works in ttl with film cameras not dslrs.

What's up with that??? Am i missing something or am i just SOL for what i want to do?

 

I did buy a dual ttl hot shoe cord made by Dot Line from B&H only to connect the flashes and watch them

both start popping off like the 4th of july. thought they were gonna explode. I also had their single cord

before i could find the nikon one and that only worked occasionally. needless to say their products are

junk.

 

The little muti flash work i've done has been relegated to full manual with said cables, or one on ttl and

one on manual at an approximate power setting. I'm just so baffled why instant wired TTL can be had with

film cameras but not digital??? Can anyone help me out, have i overlooked something?? Cheers,

 

Chris

[fraczekp]

This could be your answer to TTL with off camera flash..

 

<A HREF="

http://support.nikontech.com/cgi-bin/nikonusa.cfg/php/enduser/std_adp.php?p_faqid=13974&p_created=1146060026&p_sid=lbVoYiTi&p_accessibility=0&p_redirect=&p_lva=&p_sp=cF9zcmNoPTEmcF9zb3J0X2J5PSZwX2dyaWRzb3J0PSZwX3Jvd19jbnQ9MzEsMzEmcF9wcm9kcz04OCwxNTImcF9jYXRzPTAmcF9wdj0yLjE1MiZwX2N2PSZwX3NlYXJjaF90eXBlPWFuc3dlcnMuc2VhcmNoX25sJnBfcGFnZT0y&p_li=&p_topview=1">Nikon's KB article</a>

[scottconners]

<a href="http://michaelbass.blogspot.com/2007/01/off-camera-shoe-cords-mods-accessories.html#OCC_Splitter">Michael Bass Designs</a> might be able to help you out, he has lots of cord options for TTL stuff.

[chris_burville]

Piotr: thanks for the reference, but its honestly even more confusing. seems it is not

possible, but there's some contradiction.

 

"Digital SLR cameras D2-series, D1-series, D200 and D70 series) cannot be used for

multiple flash shooting in TTL Auto Flash mode. Multiple flash is possible with these

cameras in manual or Non-TTL Auto Flash Mode."

 

"The SC-29 is an all-in-one unit which enables connection of one external Speedlight, it

does not accept SC-26/27 or other TTL cords. The SC-28 has a TTL cord socket which

accepts these cords."

 

"If I use the SC-28 to connect multiple Speedlights using flash cords which flash setting

should I use? Set the flash mode to Manual, TTL Auto is not possible."

 

"The TTL Remote Cord SC-28/SC-29 comes with two multiple flash terminals, making

off-camera TTL flash control easy. With the F6, D2-series, the SC-29 also works as an

external AF-Assist illuminator."

 

seems to say yes and no, is there a difference between "flash cords" and "ttl cords"?? or a

difference between "TTL" and "TTL Auto"??

 

Scott: thanks for the link, i don't see one on his page but i'll have to shoot that guy an

email and see if he can whip something up for me.

 

Anyone else got clarification on this SC-28 + ttl cords thing?

[Ed_Ingold]

A multi-light setup is hardly used for snapshots. As you will find, TTL with multiple lights takes a lot of fine-tuning to get the effect you want. It is usually faster and more accurate to set everything in manual and use a flash meter. That done, you can sit an wait to ambush your "prey".

[joseph_smith3]

One reason it is confusing because Nikon flash cord product names for different things have very common names. The way I read it, you cannot have TTL if you wire the flashes together. See here for more info on product names: http://nikonusa.com/template.php?cat=1&grp=4&productNr=4801

 

Joe Smith

[frank_skomial]

Chris, there is no contradiction in all but only one of your quoted statements that is clearly wrong.

 

Specifically: "The TTL Remote Cord SC-28/SC-29 comes with two multiple flash terminals, making off-camera TTL flash control easy." - is just wrong. SC-29 does not have "two" terminals. Where did you get this quote from, it was in error.

 

The other statement has it right: "SC-29 is an all-in-one unit which enables connection of one external Speedlight," - it clearly says "one" Sppedlight, so there is no "two" terminals or two corded flashes possible.

 

The 3 prong socket on the SB-800 is for back compatibility use with older TTL mode on film cameras. The multiple flash D-TTL, and iTTL is not possible with the newer DSLR cameras using cords, as there is no provision for that in the SB-800 design.

 

The SU-800 provides corded TTL operation for alder cameras and the new macro (micro) flashes that use multiple pin sockets.

[joseph_wisniewski]

A D200 or D300 requires preflashes to do TTL.

 

Back in the "film days", we used to do TTL by having the camera fire the flashes while the shutter was open, measuring the flash that reflected off the film, and sending a "stop" or "quench" signal to the flashes when we accumulated enough energy. The camera could "quench" up to three flashes reliably when the Nikon cables connected all the trigger and quench lines together.

 

Those days are gone. Digital sensors aren't reflective enough to do it the way we did in the film days. And even if they were, off-the-film TTL was a hack to begin with. Only the wide exposure latitude color print film made it appear to work acceptably. Digital, being much mode like slide shooting, needs something better. So some clever folks came up with the idea of preflashes, before the mirror flipped up, using the camera's main metering sensors for the flash measurement. And, to allow the preflashes to be detected easier, they aren't simple flashes, but coded sequences of very fast flashes, so they can be separated from "slow" light events like sunlight, or even fluorescent light flicker.

 

Then the clever people got even more clever, and said, since we're building flashes that can send coded light messages, let's add receivers to the flashes and put information in the messages to us to individually control 16 banks of flashes on 16 different channels. (Nikon then limited it to three banks to keep the preflash time acceptable, and four channels to keep the user interface simple, but the codes are there). This means up to 10 preflashes: three command flashes to request preflash from banks 1, 2, and 3, three preflashes from the banks, a preflash from a direct connected TTL flash, and three command flashes to set power in banks 1 through 3.

 

A single, direct connected flash in TTL mode instead of commander mode is much quicker, it makes one burst for the preflash measurement, then sets the power by an electrical serial interface. This is what you want for birding, because of the speed advantage. It's as fast as digital camera TTL gets.

 

Which gets us to the horrible problem of how to use more than one flash. The answer is ugly, at best. It takes clever people to counter the camera company's clever people. There are at least two clever things that can be done. One, I call the "brute force" approach, is to modify one flash to be a "super fast" slave flash, so it picks up every pulse of light from the other flash, even the super short pulses that make up a preflash "message" burst, and duplicate them. This way, we get double the preflashes, double the main flash, in short, double the power. We'd give the modified flash (it would have to be a current generation "ultra fast" flash like an SB-800, old flashes like the venerable Vivitar 283 just don't have the speed to make short "message" pulses) an extension cable for the new fast TTL sensor, so you could position it to see the other flash. I'm not tinkering with anything that involves opening up a flash (they're somewhere between a "stun gun" and a cardiac defribulator in their dangerousness) so you'll have to find someone else to tinker one up for you.

 

The other way (the "hard way", also the way I'm currently taking) would be to build a little box that connects between the camera and two or more Nikon flashes. Outgoing messages from camera to flash (zoom to 105mm, do the preflash, get set for a main flash at 87/128 power) would just be amplified so that more than one flash could receive them without overloading the camera's serial interface. Incoming messages from flash to camera would have to be interpreted by the box and combined intelligently before being passed on to the camera.

 

I'm only at the beginning phase of the project, so it may be quite a while, unless some other clever person is also tinkering in the same direction. Actually, I've never even considered your particular problem, but it would be another market for my box. I'm really more concerned with high speed photography, but what I'm building can solve your problem, just as a "side effect" of solving mine. ;)

[chris_burville]

joseph - thank you for explaining, it makes much more sense now. I'm still surprised nikon can't come out with a dual TTL shoe cord, which in essence is what you're building. Please let me know when you finish it as i may be keen to buy one off you. best of luck. cheers,

 

Chris

[michael_bass3]

Chris-

I have done what you are asking some time ago, and had it listed on my site, but the Nikon iTTL system gives unreliable results at present. I had some pretty good Nikon pros help me in field testing, but it never worked as intended. It seems that only one flash unit can be in iTTL mode at a time, and the other needs to be in manual mode, which is not what you are really asking.

 

This dual system works just fine in the Canon world of eTTL, but again, only 2 flash units can be connected together. I have tried connecting up to 6 identical Canon 580 EX units in the initial testing, but only 2 seemd to work properly.

 

Michael

www.MichaelBassDesigns.com