What exactly is Commander Mode?

Discussion in 'Nikon' started by hbs, Jun 13, 2006.

  1. hbs

    hbs

    I am thinking of upgrading my D70s flash and have been reading numerous posts on
    this site and other literature as well. However, I'm still very confused about
    exactly what Commander Mode is, how it differs from the Master-Slave
    relationships between the camera, SB-600's, and SB-800's, and also how it
    differs from "old-fashioned" slave flashes.

    Here is what I think I understand (hopefuly most of it's correct):

    Commander Mode uses the camera's built-in flash to optically trigger external
    flashes such as the SB-600 or SB-800. In this case, all the slaves have to be
    oriented to be able to "see" the camera flash. However, I don't fully
    understand how this is different from the old traditional use of slave flashes
    that are set off by the camera's main flash. I have a suspicion that in
    Commander Mode, the flash from the camera is actually a "pre-flash" and that the
    main flash and shutter opening occur slightly after the pre-flash. This way the
    camera's flash does not participate in the exposure. Is this correct?

    If an SB-800 is mounted to the camera and operates as a master, it uses a radio
    frequency (rf) signal to trigger its slaves (which can be 600's or 800's).
    However, SB-600's cannot be master nor can the camera by itself. Would there
    ever be a situation where the camera would be operated in Commander Mode in this
    case?

    If an SB-600 is mounted to the camera hot shoe, all it can do is operate by
    itself since it cannot be a master. The camera's built-in flash would obviously
    be inoperable. Would the camera ever be operated in Commander Mode in this
    situation either?

    I hope these questions aren't too basic, but maybe they will explain why I'm so
    confused.

    Again, thanks for all the great answers that I'm sure I'll receive.

    Harvey
     
  2. "and have been reading numerous posts on this site and other literature as well" - while doing this one can loose it easily, so most of your conclusions are wrong, but few are right.

    Some basics: Commander-Remote is the relation where flash on the camera commands a remote flash - means controlls the amout of flash output of the remote flash as well as it's own light.

    Old Mater-Slave relation is when the Master flash on the camera triggers a remote flash. but does not control the amount of output of the slave flash.

    Nikon CSL uses both visible and infrared light spectrum for communications, with the exception of SU-800 commander unit that only uses infrared light. There is no radio communication used by Nikon CLS system between camera and Nikon flashes.

    Nikon uses Commander-Remote relation for Nikon iTTL, CLS modes, but in manual modes, or SU-4, you could think of it as Master-Slave relation. As usuall Nikon has them all.

    And...SB-600 cannot act as a Commander flash, it has this limitation to reduce the cost perhaps, but your D70 can act as a commander, or SB-800, or the best is SU-800.

    Now equipped with this knowledge, get back and re-think your knowledge, how that fits into your understanding. I would advice you to read more, but you already did that, perhaps reading in wrong places would not really help. I am sure others will provide more answers.

    Just read Nikon D70 and Nikon Flash Manuals, and there are good methods prescribed for each situation. The problem is to understand which applies to you. With D70 and SB-800 - all of them are applicable, but it would make more sense to use the iTTL mode, since you paid the big buks for this.

    Good Luck.
     
  3. Commander Mode was the Englishman who co-invented the toilet, or as we call it, the co-
    mode.
     
  4. Frank - "Nikon CSL uses both visible and infrared light spectrum for communications"

    Not exactly. Canon uses visible light and IR separatly, IR for communication, visible for exposure. Nikon simply doesn't care, and does all communicating with the main tube. Any flash that isn't contributing to exposure can be filtered to IR (like an SU-800, or like using an SG-3IR filter on a D70 or D200).
     
  5. Commander Mode is complex. It involves a sequence of up to ten "messages" going between the commander and the remote flashes. Each "message" is a sequence of around 60 very short flashes, like Morse code. The coded message includes a "channel" identifier, 1, 2, 3, or 4, so you can set your camera and flashes to one channel, someone else can set his to another channel, and your cameras won't trigger his flashes or visa versa.

    The commander sends up to 7 messages, and the remotes in groups A, B, and C each send a message back to the commander.

    1) The commander sends a message that basically says "group A flashes, please preflash now". (OK, in my interpretation, the commander is polite).

    2) All the flashes set to group A do their preflashes. The preflashes are coded sequences of pulses, so the camera can use DSP (digital signal processing) to extract the preflash signal from optical "noise" such as sunlight or the flickering room fluorescent lights.

    3) the camera measures the preflash from group A.

    4) D70, D200, SB-800 (in commander mode) or SU-800 repeat steps 1, 2, and 3 for group B. D70 only does group A.

    5) SB-800 (in commander mode) or SU-800 repeat steps 1, 2, and 3 for group C. D200 only does groups A and B.

    6) if D200 or SB-800 (in commander mode) are also set to contribute to the picture, they do their own preflashes now, repeating steps 2 and 3 yet again.

    7) the camera takes the results of the measurements from groups A, B, C, the commander (if set to contribute to the picture) and the ambient light, puts it all together along with your settings for lighting ratio, and calculates the exposure values for camera and all flashes.

    8) the commander now sends out the group A control message: something like "group A flashes, set to 1/4 power and wait for the trigger 'pop'. If there isn't a "pop" within a window of a few mS, the group A flashes close the "window" on the trigger "pop" and go back to waiting for messages. There's virtually no way for a pop from someone else's flash to trigger your primed group A flashes: it would have to hit that few mS window.

    9) the commander sends the group B control message

    10) the commander sends the group C control message

    11) the shutter opens, and the commander either does a little "pop" of a flash to trigger all the remotes that were "primed" in steps 8, 9, and 10, or it makes a bigger flash if it were set to contribute to the exposure.

    Aren't you glad you asked?

    ;)
     
  6. Harvey S , jun 13, 2006; 08:58 p.m.
    <br>[snip]
    <br>&gt; Commander Mode uses the camera's built-in flash to optically
    <br>&gt; trigger external flashes such as the SB-600 or SB-800. In
    <br>&gt; this case, all the slaves have to be oriented to be able to
    <br>&gt; &quot;see&quot; the camera flash. However, I don't fully understand
    <br>&gt; how this is different from the old traditional use of slave
    <br>&gt; flashes that are set off by the camera's main flash.
    <br>
    <br>The difference is where the flash is being controlled from. In Commander mode, the built-in flash fires a pulsed signal of light that tells the remote flash units to fire their pre-flash bursts. The camera's meter then reads the scene during the pre-flash burst and based on that, it determines what the correct flash output should be. It then uses its built-in flash to fire another pulsed signal telling the remotes to fire again, this time using the output as calculated by the camera.
    <br>
    <br>With the old style slave flash units, any flash unit would trigger them, and their output was either manually controlled (by settings on the back of each unit) or automatically controlled (each unit measuring the light using their own built-in sensors).
    <br>
    <br>BTW, notice that my description of COMMANDER mode flash did not mention anything about the built-in flash illuminating the scene. It might provide enough illumination if the subject happened to be very close to the camera, but generally speaking, its light output is only used to send optical control signals to the remote flash units. The build-in flash doesn't even provide a pre-flash burst to measure the scene's brightness. Pre-flash is ONLY done by the remote flash units.
    <br>
    <br>&gt; If an SB-800 is mounted to the camera and operates as a
    <br>&gt; master, it uses a radio frequency (rf) signal to trigger its
    <br>&gt; slaves (which can be 600's or 800's).
    <br>
    <br>It uses light signals, not RF.
    <br>
    <br>&gt; However, SB-600's
    <br>&gt; cannot be master nor can the camera by itself.
    <br>
    <br>True.
    <br>
    <br>&gt; Would there
    <br>&gt; ever be a situation where the camera would be operated in
    <br>&gt; Commander Mode in this case?
    <br>
    <br>I'm not sure what you're asking. I mean, of course the camera can be operated in Commander mode. It's built-in flash unit supports this ability. Using the built-in flash, you can control any number of SB800's and 600's remotely. However, in Commander mode, you can only control ONE group of flash units, so they would all be using the same light output. You can't, for instance, trigger one group set to 0 ev and another set to -1 ev.
    <br>
    <br>&gt; If an SB-600 is mounted to the camera hot shoe, all it can
    <br>&gt; do is operate by itself since it cannot be a master. The
    <br>&gt; camera's built-in flash would obviously be inoperable. Would
    <br>&gt; the camera ever be operated in Commander Mode in this
    <br>&gt; situation either?
    <br>
    <br>Correct, with the SB600 mounted on the camera, it could never control another SB flash unit via Commander or Master mode.
    <br>
    <br>BTW, I noticed that there is a bit of confusion in the answers to your question. In particular, people don't seem to be discerning between MASTER and COMMANDER modes. MASTER supports multiple groups of flash units, COMMANDER supports only one.
    <br>
    <br>&gt; The commander sends up to 7 messages, and the remotes in groups A, B, and C
    <br>&gt; each send a message back to the commander.
    <br>
    <br>Technically, the above quote is wrong because Commander mode sends commands to only ONE group. Master mode, however, will communicate with multiple groups. The distinction is important because then it becomes apparent why the D70 is limited to controlling only one group: it only supports COMMANDER mode.
    <br>
    <br>&gt; Some basics: Commander-Remote is the relation where flash on the
    <br>&gt; camera commands a remote flash - means controlls the amout of
    <br>&gt; flash output of the remote flash as well as it's own light.
    <br>
    <br>A flash unit that is operating in Commander mode does not control output of its own light in the sense that it is contributing illumination to the scene. It is only using its output to control a remote flash group. If its light output happens to also alter the scene's illumination, it is entirely by accident.
    <br>
    <br>larsbc
     
  7. hbs

    hbs

    Thank you, everyone. I suspected that Commander Mode might be more complex than I had originally thought and it appears I was right. I also appreciate the clarification of rf vs. IR as the communications method. This does leave me a bit puzzled, however. On one of the Nikon sites that I visited was an example of multiple flashes to illuminate an automobile being photographed. Among the approximately 5 slave flashes was one behind the car and one inside. These two did not appear to be in line-of-sight of the camera (or Master) which is why I suspected rf (not IR) communication. My judgement must have been wrong.
     
  8. Larry - "BTW, I noticed that there is a bit of confusion in the answers to your question. In particular, people don't seem to be discerning between MASTER and COMMANDER modes. MASTER supports multiple groups of flash units, COMMANDER supports only one."
    If you are confused, simply reread what I posted, because it is totally correct. (and incidentally, there is no need to SHOUT). There is no discerning between "master" and "commander" modes.
    The oldest manuals, such as that of the SB-800, the first iTTL device, use the term "master". Although photographers have been using the terms "master" and "slave" for many decades, this was deemed a "sensitive" issue, so more recent manuals, like those for the D70, D200, and SU-800 replace the term "master" with the more politically correct term "commander".
    The D200 "commander mode" is virtually identical to the SB-800 "master mode". The only difference is that the D200 only supports channels A and B (for reasons unknown). You can vary the lighting ratio between the D200 on board flash and remote groups A and B exactly how you'd vary the ratios between a camera mounted (or SC cord connected) SB-800 and remote groups A, B, and C. The D200 menu layout even matches the SB-800 menu.
    SB-800 "master" menu
    M TTL +0.3
    A TTL -0.3
    B ---
    C ---
    D200 "commander" menu
    Built-in TTL +0.3
    Group A TTL -0.3
    Group B ---
    The SU-200 manual attempts to "train" us. The word "commander" occurs 173 times, but a few times near the beginning of the book, they use the term "master/commander", just to let us know a "commander" is a "master". (note: I was not impressed by the movie "Master and Commander").
    Your observation that "Pre-flash is ONLY done by the remote flash units" is also in error. Both SB-800 and D200 can be set to allow you to control the ratio of the camera mounted flash to groups A, B, and (for SB-800) C. If you select anything other than "---" for "Built-in" on a D200 or "M" on an SB-800, it will indeed preflash.
    So, the very most complicated bunch of messages is, indeed, when you have an SB-800 with all four banks, M, A, B, and C set to TTL. That results in the sequence of 10 messages that I described. (preflashes are messages, too. The camera and flashes decode them with the same DSP techniques).
     
  9. "There is no discerning between "master" and "commander" modes."

    Friend of mine uses SB-600 in Manual mode, to trigger remote studio flashes via optical slaves.

    That certainly is not a commander mode. All of you agreed that SB-600 cannot be a commander. So what would you like to call SB-600 in this capacity ?

    SB-600 acts like an old and good Master flash on the camera, triggering all other flashes. So, discerning or not discerning, it just works OK. So, there must be a difference between Commander and Master, in certain cases.
     
  10. Frank - "Friend of mine uses SB-600 in Manual mode, to trigger remote studio flashes via optical slaves. That certainly is not a commander mode. All of you agreed that SB-600 cannot be a commander. So what would you like to call SB-600 in this capacity ?"

    You said it yourself. We call that "manual mode".

    It's not "master mode" or "commander mode", because SB-800 "master mode" is just like D200 and D70 "commander mode": both use preflashes so they can't trigger studio strobes. You put the flash into "manual mode", and dial down the power, to trigger your studio lights. Set an SB-800 to 1/128 or 1/64 power, a D200 to 1/32 or 1/16 power, a D70 to 1/16 power.
     
  11. Joseph,

    The SB-600 works in the manual setup works like the old and well established Master flash.

    All what it does, emits a single flash during exposure time, and at the same time triggers all remote slave flashes. Since there are many flashes contributing to the exposure, only one is the master, and that is the SB-600, while all others are slave flashes.

    So SB-600 is a Master flash sitting on the camera and triggering all slaves.

    This concept seems to be as simple as it can possibly be.
     
  12. Frank, Harvey asked exactly what "commander mode" was. Larry threw in a very confusing post about "COMMANDER MODE" and "MASTER MODE", and how different they were. I explained exactly how Nikon uses the terms "commander mode" and "master mode" in their documentation.

    Now, you can go on and on about how you use a flash to do what you would have called "master" years ago, before things like iTTL or E-TTL II from Canon, but that is neither here nor there, because what you're doing is not labeled "master mode" in any documentation.

    It's like the difference between controlling the shutter speed in manual mode, and actually putting the camera into shutter preferred mode.

    I don't know why you feel a need to argue about this. After all...

    This concept seems to be as simple as it can possibly be.
     

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