Mix of TTL and Manual flashes

InsuredDisasterInsuredDisaster Registered Users Posts: 1,132 Major grins
edited March 8, 2011 in Technique
I have a question that I hope you might be able to answer. I'm interested in some of the inexpensive Chinese flashes, but the task I need them for involves rapidly varying flash to subject distance. I'm hoping to increase the number of speedlights to increase maximum power and improve recycling times as well as increase some flexibility.

My question is this: If I use my SB-800 to trigger the Sb-600's via CLS-TTL, and have the manual flashes set to a given level, will the TTL system increase or decrease the TTL flashes as needed to balance out the light. ie, subject moves further away, manual flashes remain on say 1/4 power, but the TTL increases to 1/2 power, then as the subject moves closer, the manual flashes remain on 1/4 power but TTL based flashes drop to 1/16th power?

The optical triggers supposedly ignore monitor preflashes and I'm not really concerned about actually triggering them, just how the TTL based flashes would perform in this setup.

Comments

  • angevin1angevin1 Registered Users Posts: 3,403 Major grins
    edited March 7, 2011
    I have a question that I hope you might be able to answer. I'm interested in some of the inexpensive Chinese flashes, but the task I need them for involves rapidly varying flash to subject distance. I'm hoping to increase the number of speedlights to increase maximum power and improve recycling times as well as increase some flexibility.

    My question is this: If I use my SB-800 to trigger the Sb-600's via CLS-TTL, and have the manual flashes set to a given level, will the TTL system increase or decrease the TTL flashes as needed to balance out the light. ie, subject moves further away, manual flashes remain on say 1/4 power, but the TTL increases to 1/2 power, then as the subject moves closer, the manual flashes remain on 1/4 power but TTL based flashes drop to 1/16th power?

    The optical triggers supposedly ignore monitor preflashes and I'm not really concerned about actually triggering them, just how the TTL based flashes would perform in this setup.

    I think what you ask is a very good question, and one if I had, I'd simply try it to find out the answer. I have used the CLS system pretty extensively, but I've gotten away in the last year or so from using TTL. From what knowledge I do have, I'd say yes if the lights are aimed at the subject and that subject is what is giving the CLS feedback to lighting. But somehow I cannot imagine such a perfect world.

    I say try it out! You don't need the other flashes to see if TTL is going to react.
    tom wise
  • QarikQarik Registered Users Posts: 4,959 Major grins
    edited March 7, 2011
    I suspect that the i-TTL will not know about the existence of the manual flashes and as just as if they were not there. This is becasue i-ttl uses imperceptible preflashes to setup your exposure pre shot instead of during exposure. If you had "true" ttl then it may adjust for the manul flashes but I don't think modern flash have true ttl?
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  • ziggy53ziggy53 Super Moderators Posts: 24,132 moderator
    edited March 7, 2011
    Qarik wrote: »
    I suspect that the i-TTL will not know about the existence of the manual flashes and as just as if they were not there. This is becasue i-ttl uses imperceptible preflashes to setup your exposure pre shot instead of during exposure. If you had "true" ttl then it may adjust for the manul flashes but I don't think modern flash have true ttl?

    Correct. In modern dSLR cameras they use the pre-flash information before the main exposure to set the flash output. A modern camera's flash exposure system would not necessarily measure the manual flash exposure contribution at all.

    If the manual flash is triggered via a "pc" connection then it will fire during "image capture" but the camera has no way of knowing its contribution of light.

    If you plan on using an optical slave then it should be of the "digital" slave variety for contributed flash or the optical slave will trigger during pre-flash. In that case the camera "would" sense the slaved flash contribution but, since it cannot control the manual flash output, the exposure will be uncontrolled and unpredictable.

    If you use a remote flash with an "auto" capability then that flash will control its own exposure contribution via its own sensor and the flash settings.

    Bottom line, mixing manual flashes and TTL flashes is rarely beneficial and the only time I have used that combination purposely and successfully is using the TTL flash(es) for primary/key and fill light and then using a manual flash for either rim/hair and/or background light.

    For the original poster's application I would go with all iTTL flashes and use (at least) 2 groups to allow different flash settings by group.
    ziggy53
    Moderator of the Cameras and Accessories forums
  • Art ScottArt Scott Registered Users Posts: 8,959 Major grins
    edited March 7, 2011
    Qarik wrote: »
    . If you had "true" ttl then it may adjust for the manul flashes but I don't think modern flash have true ttl?

    It is actually TRUE TTL....the new digital cams still read "thru the lens" - ttl.........
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  • InsuredDisasterInsuredDisaster Registered Users Posts: 1,132 Major grins
    edited March 8, 2011
    Well, I just realized that the other day I had two flashes in the background set to manual output (SB-600's) and then the onboard SB-800 commander was set to TTL output. Things seemed to work out ok but maybe I'll test it more under more controled circumstances. We'll see.
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