Rear curtain sync and optical flash trigger

[absent]

<p>I recently bought an optical flash trigger to fire a second strobe for a home portrait setup. I'll be using a Nikon SB-600 on my D5100 as the main flash. I know that pre-flashes from the TTL system can cause the slave flash to trigger early. My question is, can I get around this by using rear curtain sync? If the pre-flash triggers the slave early, will the shutter be opening already?<br>

　<br>

Or, will the slave flash foul up the flash meter reading so much that I must just use manual flash mode? Thanks for any help.</p>

[bebu_lamar]

<p>I think that would trigger your flash okay but it would mess up the TTL system. The TTL system would fire the preflash and the remote flash and then it sees way too much light due to the remote flash which it isn't aware of and would cut down the main flash power significantly. <br>

It much easier to do the whole thing in manual no preflash whatoever. </p>

[ann_overland]

<p>There will be pre-flashes prior to the rear curtain flash sync mode too. You have to go manual to avoid the preflashes that fires a slave too early.</p>

<p>When the pre-flashes trigger the slave, the light from the slave unit is emitted too early for the light from the slave to be part of the lighting of the photo. And the slave is not able to communicate with the TTL flash exposure units, so it will not be messing up the TTL units working together for the correct lighting of the photo. In short: It works as if you didn't use the slave unit at all.</p>

[bebu_lamar]

<p>Using multiple flash with i-TTL is quite complicated and only works if you have CLS flashes. If the preflash fires the slave and the slave fires the same time without much delay the camera metering system would see the light from the slave which it thinks coming from itself and so it would set the power level really low for the actual exposure. </p>

[ann_overland]

<p>Well, it doesn't see that light, BeBu. Not with my CLS flashes and a slave, anyway.<br>

<br /> Edit: At least there is no noticable difference in the exposures to my eyes.</p>

[absent]

<p>Thanks - I suspected that was the case but appreciate confirmation. Neither the D5100's popup flash nor the SB-600 can be used as "commander" so I guess I'll have to go manual.</p>

<p>Any advice on setting multiple flash exposure using guide numbers, or is there a reference I should read? Should I, for instance, set each flash close enough to require f/4, and then stop the lens down to f/5.6?</p>

[bebu_lamar]

<p>Make a guess, take test shot and adjust. My initial guess would be f/5.6@ISO100 or f/8.0@ISO200. </p>

[jcuknz]

<p>Maybe you have a reason for placing the SB-600 on the camera as your main flash but why not have both flash units off the camera and trigger them with their own optical triggers with the camera's on-board flash ... if you don't want light coming from the direction of the camera you can always shield it either with your finger or a piece of card so that enough escapes to trigger the remote units but not enough to be seen in the photo.<br>

Working in a home studio as I assume you are it is easy enough to make an innitial stab at what aperture to use and then consult the histogram in review. The aperture depends on the flash to subject distance of each unit as well as any level settings of the units along with the balance of lighting your require for artistic reasons.</p>

[absent]

<p>I was thinking of using the Sunpak high and to one side as the key light, and the SB-600 as the fill. I have one of those Tupperware (Gary Fong) contraptions for the Sunpak, and thought about using a diffuser on the SB-600 and bouncing some light off the ceiling. I could remote the SB-600 as you suggest but would have to buy another flash trigger and a light stand (or third tripod).</p>

[rodeo_joe1]

<p>"My question is, can I get around this by using rear curtain sync?" - Short answer, No!<br>

The slave flash will still fire before the camera shutter has even opened. You need to forget about CLS and all that crap and go to pure manual control of your flashes. Set the camera to manual, with a shutter speed of 1/250th at whatever aperture and set the power on the SB-600 manually. The optical slave will then work OK. You'll have to either meter the flash exposure or set it by trial and error from test exposures.</p>

<p>Or follow J C's suggestion and use the camera menu to set the camera's popup flash to manual as well.</p>

[ann_overland]

<blockquote>

<p>..why not have both flash units off the camera and trigger them with their own optical triggers with the camera's on-board flash..</p>

</blockquote>

<p>+1<br>

Sooner or later I guess you would want to work with three flashes. Just wait and see :-)</p>

[ian_casement]

<blockquote>

<p>Well, it doesn't see that light, BeBu. Not with my CLS flashes and a slave, anyway.</p>

 

</blockquote>

<p>Clever things those CLS flashes.. especially the SU-4 slave function. It ignores pre-flashes from iTTL and just syncs on the shutter</p>