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Question about CLS using the onboard flash as the master

Discussion in 'General flash photography, lighting, and technique' started by bigwilly, Jul 30, 2009.

  1. bigwilly

    bigwilly

    143
    Oct 19, 2007
    Toronto
    Ok so my cousin asked me this and at first I thought he was doing something wrong, then I tried it myself with the same results. I have used CLS with the onboard flash to trigger my SB800 and SB600 in the past but I have never noticed this nor I have I used it with this lens.

    The issue is this, supposedly if you set the built in flash as commander mode and set it to "--" it will not contribute light to the image.
    Well we just tried now with our wide angle lenses, him with his 18-105mm on a D90 and me with my 17-55m on my D300. You can clearly see the shadow from the lens hood in the image. So the question is if the onboard flash is not supposed to be contributing light to the photo why the shadow?
     
  2. Pre-flashes.

    Before each capture, the commander flash sends out a series of small flashes to determine the right flash exposure for the scene and signal the remote flashes to fire (and at what power). If your settings are low enough (high ISO, wide open, long shutter) and your subject is close the pre-flashes will contribute to your capture.

    Turn off the remote flashes (by setting group A and b to "--") and the pre-flashes will disappear as well.
     
  3. bigwilly

    bigwilly

    143
    Oct 19, 2007
    Toronto
    I am aware of the requirements for the pre-flash for the signalling, basically it is mis-leading when they say "--" will not contribute light to the image, even at ISO 200 and 1/60th f/2.8 there is still light and consequently shadow contributed from the onboard flash.
     
  4. mvnsnd

    mvnsnd

    626
    Jul 12, 2008
    Western NY
    I think if you really don't want the light to contribute to the photo, you have to place an IR filter in front of the pop-up flash. This reduces visible light, but still allows the CLS communications. Like this.
     
  5. bigwilly

    bigwilly

    143
    Oct 19, 2007
    Toronto
    I saw that mentioned before, thanks for the tip.
     
  6. Silenus

    Silenus

    483
    Dec 19, 2008
    Ronkonkoma, NY
    The pre flashes have nothing to do with the shadow since they are occurring before the shutter opens. However, there is and must be a final sync flash to trigger the other flashes at the proper moment to fire. This occurs with the shutter open. Now...the thing is that when the commander is set to "--" the final sync flash is a very low power so that MOST of the time the amount of light is negligible to the exposure and won't ever be noticed.

    However it can be noticed under certain situations such as: 1) camera is set very wide aperture or high ISO and is thus very sensitive to even that small amount of light from the sync flash, 2)you are shooting something very reflective/shiny so the highlight from the flash is visible in the object, 3)you are very close to what you are shooting and thus is power of even that low power flash is amplified due to the close distance.
     
  7. You could also spend a few $$ and get an SU800 whcih would eliminate the requirement of using the onboard flash period.

    AM
     
  8. Yes, and all these small bursts of flashes that occur before the main flash fires are still called pre-flashes.

    ---

    You can can get a better idea of the number of pre-flash bursts and when they occur by setting the camera to rear curtain sync, long shutter and use either exposure delay or mirror-lock up mode if you have it to delay the actual exposure. You'll see:

    1) Burst just before mirror goes up for flash exposure metering - doesn't appear if you use FV lock or set the remote flashes to manual,
    2) Burst just before exposure starts - tells each flash group what their settings should be (power),
    3) Final burst just before the exposure ends (because of rear curtain sync) - tells each remote flash to actually fire. This is the pre-flash that can contribute to the overall exposure.

    Fun stuff!
     
  9. 73Z1

    73Z1

    Sep 15, 2008
    Sacramento
    As Sinelus said, these don't contribute to the exposure, because they occur before the shutter is opened. These preflashes are for iTTL metering and should not affect the exposure.


    Yes, very true, the signal to fire does occur with the shutter open and can show up in the exposure. That is the root cause of the OPs problem.


    If you set Group A and Group B to -- neither group will fire and you have no remote flash. I assume that you are joking?


    While #3 is technically correct, I feel that it is misleading. The final sync burst will occur when one uses front curtain sync as well.

    #1 is correct, but could be misleading to a newbie. If anyone thinks using FV lock on the camera or Manual mode settings for the remotes will stop the final sync flash from contributing to the exposure, they will be disappointed. Short of blocking the white light with a filter like the Nikon SG-31R, the final sync flash will always contribute to the exposure when using speedlights in remote AWL modes. Put a speedlight in remote mode and set the camera commander mode to -- for the camera built-in flash and Group B. Set manual 1/128 for Group A in the camera's commander mode. Set camera to ISO 1600. Set speedlight to remote Group A. Point the camera in portrait orientation at a dark wall with the lens set to widest focal length and have the flash pointed at the wall base or floor. Trigger the shutter and some light from the flash should appear at the bottom of the frame showing the flash fired in sync. The shadow of the lens hood of an 18-200VR or other wide angle lens will easily be seen on the wall. That is because the final sync flash is contributing to the exposure. Pointing the remote away from the subject more clearly reveals this, as the OP has found out.

    In short, if you don't want the in-camera flash to contribute any light to the exposure, get an SG-31R ($14.95 at bocaphoto.com) or an SU-800. Otherwise, lower ISO with smaller apertures requiring greater flash power will help to negate the effect.
     
  10. Well thanks for taking the time and over analyzing everything I wrote, but I wasn't trying to describe every single possible minutia involved, but hey, thanks for doing it for me.
     
  11. While you have the basic idea, the actual preflash sequence is a bit different from what you described.

    The commander sends out a sequence of preflash pulses beginning with itself. Then a sequence of preflashes is sent to group A and the group A flash (if set to TTL) returns a sequence of pulses. In this time sequence, the scene reflectivity is measured and the power setting of group A is determined and sent to the group A remotes. The commander sends out a total of three pulses for Group A and the Group A remote responds with two pulses. These pulses contain (at least) the group identifier, any exposure compensation, and finally the commanded power setting. This is the last activity dealing with group A until the "fire" signal.

    Then the same thing happens with Group B and so on. In other words, the Monitor Preflashes, associated flash metering, and power instructions are done on a group by group basis with Group A completing all the required communication and calculating before Group B is addressed. This seems odd, but in fact the power setting for one group is completely determined before any information from subsequent groups is gathered.

    That means that AWL doesn't try to adjust for two groups illuminating the same subject. It is left up to the photographer to add or subtract exposure compensation as necessary.

    If a particular group is set to Manual, then that group of remotes doesn't return the normal two pulse sequence (no need). However, the commander does send a three pulse sequence to the group which is set to manual, and that's how that group knows the fractional power setting selected by the photographer.

    The above described activity does indeed happen when you use FV lock, except that it occurs when you press the FV button as opposed to just before the shutter opens. Additionally, all this preflash activity occurs with the mirror still down. Nothing happens between the time when the mirror goes up and the shutter starts to move.

    Finally, the shutter opens, the commander sends out a single "fire" pulse, and the remotes all fire together. Is this last signal a preflash? I suppose it depends on if you define the "pre" to mean prior to the shutter opening or prior to the remotes firing. As far as I know, Nikon doesn't reveal their thoughts on this.
     
  12. 3LPCPhotography

    3LPCPhotography

    467
    Oct 30, 2008
    Canada
    When the commander is set to "--" there is some low level light from the commander flash. I've checked this numerous times. It's usually only a problem for closer shots, especially macros.

    the work around is, highest cost to lowest, an SU-800 wireless commander, a flash cable like the SC-29, or the inexpensive light blocking SG-31R ir blocking panel.

    Tom
     
  13. Common problem.
    This solves it.

    http://www.bhphotovideo.com/bnh/con...rch=yes&O=jsp/deadEnd1.jsp&A=search&Q=*&bhs=t

    [​IMG]

    Can also be solved by using an infrared lens filter over your flash.

    Go buy some PW, cybersynchs, cactus triggers, cords, and forget that CLS mumbo jumbo.
     
  14. LeeF

    LeeF

    327
    May 24, 2008
    Massachusetts, USA
    I ran into a similar problem as you. The on board flash did not contribute tothe exposure BUT it did result in a small objectionable reflection in the center of the image.

    I solved this problem by holding a 4x4 piece of cardboard above the lens thereby blocking the direct light from the on board flash.

    The 2 remote SB800's still 'saw' the flash and operated as expected.


    Good luck.
     
  15. garyosborne

    garyosborne Guest

    lol @ cools.....just put your hand in front of it for the odd shot where it's an issue, as said it only occurs in set circumstances
     
  16. Growltiger

    Growltiger Administrator Administrator

    If you put your hand in front it may not trigger the other flash! The device shown two messages above is the solution.
     
  17. ArtScott

    ArtScott

    Jul 11, 2009
    WICHITA, KS
    Sorry to revive such an old thread............as a newbie to the Nikon Digital CLS family......the pop up has a shorter working range than the SU-800 or a MASTER SB900......
    My question is............

    What is the working range of the pop up as commander with the SG-3IR ???

    Much easier to spend $16 (B&H) than the 260+ for the SU-800
     
  18. WayneF

    WayneF

    Apr 3, 2006
    Texas

    Several things seem wrong here... :smile:

    I suspect the internal flash commander has greater range than the SU-800. At least UncleFrank showed a test outdoors awhile back that showed it approached double range. My vague and untrustworthy memory recalls his result outdoors was something like 100+ feet Internal vs maybe about 58 feet SU-800??? This was centered, without SG-3IR panel. He said its reflections were stronger around corners indoors too (worked vs did not work in the hallway, I think he said). Perhaps Frank can mention that again?

    The SU-800 specs say 66 feet (page 130).

    The SG-3IR is only needed for macro work, or for very close work which might generate a catchlight. It ships with the R1 macro kit. The triggering flash is very weak, it cannot illuminate the scene. See this for example:

    https://www.nikoncafe.com/vforums/showthread.php?t=243708#5

    That result is BLACK at about 6 feet. I cannot imagine using the IR panel at long distances, or being concerned about distance with it.

    But, to keep in the spirit, I just tried my D300 internal flash Commander with the SG-3IR and SB-800 remote. I zoomed the lens to 24mm, and turned the camera so that the distant SB-800 was just barely in the frame (at the far edge), which I think puts the flash nearly 40 degrees off center (more than spec, but like it might be used?). With the flash sensor pointed at the commander, it triggered easily first time at about 54 feet. This is not a maximum or a comparison. I think it should do more, but that was all the room I had. This is with the SG-3IR, which I cannot imagine needing in that situation.
     
    Last edited by a moderator: Mar 15, 2017
  19. ArtScott

    ArtScott

    Jul 11, 2009
    WICHITA, KS
    Wayne,
    Here is my dilemma.......I have a couple of SB900's but not enuff to do a lot of the shooting I do.....now comes into play optically triggered flashes.....the preflash of the pop up....pops the optically triggered flashes......now I am under exposed by several stops as it seems that when the OPT flashes fire that is read by the Commander also and everything is turned waaaaaay so to speak.....

    I was hoping I could also use my pc sync connection and RF triggers to slave flashes but it seems that when ever the pop up is up or anything connects to the hotshoe it disables the sync port......
    need a good solution so I can get totally battery operated and MOBILE (pronounced as MOE - BILE....not mobull :-}} )
     
  20. WayneF

    WayneF

    Apr 3, 2006
    Texas
    As I understand it, your complaint is that the remote flash system is underexposing. Several stops seems unimaginable, but up to one stop is not uncommon. That is not anything the SG-3IR will help. The metered preflashes occur before the shutter opens (and they come from the remotes). The IR shield blocks a very weak "Everybody Fire Now!" commander signal which will not contribute to any exposure over a few feet.

    Make sure you are watching the Ready LED, that it is recycling OK without blinking the insufficient flash power warning. If you get the warning, you will underexpose. Open aperture and/or increase ISO. Also make sure you know what your Flash and Exposure compensation setting are (three of them, including Commander menu).

    The "several stops" is a huge concern, and that must be some other problem - but if no abnormal problem, just apply whatever flash compensation is necessary. We always have to pay attention and stand ready with flash compensation.

    Yes, camera PC sync is disabled if the internal flash door is open.

    If necessary, you "could" get around that by using a SB-800 or SB-900 as the commander on the hot shoe. Then the flashes PC sync connector (as commander) is not disabled (but it is disabled if configured as a Remote).

    But the real idea is that you need to choose... you ought to be using an all manual flash system, or using the Nikon Commander system. Not both at same time.
     
    Last edited by a moderator: Dec 17, 2009
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