ML-L3 with two cameras - does it fire both?

Discussion in 'Nikon' started by ilkka_nissila, Jun 15, 2008.

  1. I have a question about the wireless remote control for the D40 (ML-L3). I take
    it that since it is an accessory item, it should trigger all of the compatible
    cameras which are in range and expecting the signal?

    I suppose I have to test it at a store to be sure. I am building a minimum cost
    stereo photogrammetry setup and am trying to be sure they can be fired
    simultaneously ... so that I can have one of the cameras fire its flash, and the
    other camera would just have its shutter conveniently open when the flash comes.
    I guess I could use a little longer exposure time just to be sure that the flash
    is seen by both cameras.

    I think I need to use a flash which is operated in a non-i-TTL mode. If the
    first camera fires the preflashes (i-TTL), this would mean that the second
    camera takes its picture before the flash is "properly" fired.
     
  2. You can be pretty sure that one remote can trigger two or more cameras. After
    all there is surely no way for the remote to be aware of how many cameras are
    "listening" to it. The only way it could fail would be for the camera to send
    some signal back to the remote and tell it to stop signaling and I'm sure there
    is no need for that.

    Thinking as I write .....

    Of more concern is the flash sync since the time from receipt of the remote
    signal to the shutter being fully open is probably not very well defined.

    If camera A gets its shutter open before camera B and fires its flash then
    camera B may not see the flash because its shutter is not open yet. Remember
    that the flash occurs the instant the sensor is fully uncovered. Using a lower
    speed won't help here.

    If you use rear curtain sync you will have a similar problem if camera B closes
    it's shutter before camera A has fired its flash.

    I wonder if it might be better to set the shutter to 1/500 sec and use flash on
    both cameras, hoping that you don't capture both flashes in error and get 1 stop
    over exposure. You are betting on the difference in delay to open being
    **more** than 1/500 second.

    I guess you need some experiment to determine the trigger to shutter open delay
    and its variability.

    Feel free to shoot me down.

    Richard
     
  3. I would prefer both images to be taken with just one flash, since they may be easier to match in the subsequent processing if the light doesn't change between shots.

    I think if I use 1/125s in camera A and 1/60s in camera B, when camera A fires its flash, if it's using rear-curtain sync, then both cameras should record the flashes. I will soon find out ;-)
     
  4. That might do it so long as the ambient light isn't enough to cause a problem
    with difference in speeds.

    Had another thought. If you actually ensure you are using i-TTL with the
    preflash then the extra delay for the preflash and processing time could well be
    enough to ensure that the other camera has its shutter fully open if you use say
    1/30 second. One doubt would be that you might record the preflash on the other
    camera giving a double image if there is motion. On the other hand the preflash
    is very dim so it might not matter.


    Good luck.

    Richard
     
  5. I couldn't get it to work. Basically the firing of the cameras was erratic. Sometimes both cameras didn't fire. Sometimes they did but the timing was not synchronous enough that I could get the same flash exposure. I think I got one pair of pictures where the result was satisfactory, and then I took another where the other camera completely missed the flash.

    I am surprised by this, I went through all the relevant menus and made sure the cameras had the same settings. The remote control seems to be quite sensitive to how you point it in relation to the cameras but I couldn't find a position where the cameras would fire at the same time with adequate precision.

    I will try the same with my own cameras, which use the MC-30 type releases (I can hack together a cable which triggers two cameras at the same time). Maybe it will work.
     
  6. I think I can think of a plausible reason why the cameras don't fire at the same moment. If one of the cameras receives a lower intensity signal from the remote (due to a different relative position), and if it integrates this signal then the threshold would be exceeded first in the camera which sees the stronger intensity.

    I can't purchase D200's new in Finland any more, it seems, so I suppose I'm off to search for two second hand cameras.
     
  7. Weird.

    Just how long is the difference in timing?

    Is it so long that you can actually hear the shutters opening at different times for example?

    I wouldn't have expected there to be any integration time. My guess is that these devices use a digital signal modulated onto an infra red carrier which is how TV remote controls work - in fact I think some people have even used TV remotes for Nikon cameras! If that is the case then reception should be OK just so long as the received signal exceeds some threshold.

    Are you sure the remote is not at too great an angle to work reliably with both cameras?

    You do need to repeatedly reset the remote mode after a picture is taken don't you - I'm sure you'd done that!!

    Were you on manual focus? Manual exposure would be a good idea too just to eliminate another uncertainty.

    After I wrote last I did wonder if the firmware in the camera polls the IR receiver at a rather low rate and that this might cause a timing variation.
     
  8. On the D40X which I tested today, you don't need to reset the remote mode unless a certain amount of time passes, after which the camera returns to S mode. It stays for about a minute expecting the remote to be used, and you can take multiple pictures.

    I was in manual focus and manual exposure modes. Also the flash was firing manually (when I was using an external flash). I don't remember exactly but I would guess that the delay was of the order of tens of milliseconds. If I used a shutter speed of 1/15s or so, I would increase the probability of the flash being recorded by the secondary camera but then I was getting too much of ambient light in the picture. It wasn't an ideal test environment. It's important that the exposure times of both cameras are comparable so that ambient light doesn't influence the pictures differently. Of course it might be possible to shoot with the lab room dimmed but it's an extra source of potential hassle and makes it more difficult to make sure the camera is at the correct distance.

    Yes, it may be possible that the camera is polling the receiver at intervals. This could explain what is happening. Thanks.

    I could use the built-in flashes of both cameras and let them do their thing but then the reflections from the light sources would be in different places in the two images, making it more difficult to automatically detect matching points in the two images. Also I would really prefer to get the shots as simultaneously as possible. My subject is potentially moving (though not always).
     
  9. Ah - I thought you'd have to reset the mode to remote after a successful
    release. On my D40 you have to do that after using the self timer and I'd
    thought the remote would be the same (I don't have a remote control yet).

    On thinking about it some more it seems quite likely that slow polling is
    causing the delay variation since it's quite likely the on board microprocessor
    will be in a low power mode while it waits for the remote signal. I guess it
    could be several minutes if you set it up that way (remote on duration up to 15
    minutes).

    Oh well, I guess wiring two cameras together sounds OK ...............
     
  10. I talked to a shop guy who said that Sigma sold some DSLRs for stereo imaging so
    that firing the cameras at the same time was actually a supported feature,. I will
    investigate the Canon option first. Then 2nd hand Nikons, if the Canons don't fire at the
    same time.
     
  11. I would be inclined to place speedlights on both units in I-TTL. I often use two flashes with one tilted up with a diffuser, and the other pointed at the subject from an angle to the left or right. It seems to me that both cameras will be triggered at the same time, and will recognize they are both attached to flashes, using similar processing times to shutter release. Interesting challenge though...
     
  12. They're not activated at the same time, at least if the cameras are D40X's. Each
    camera will image the light caused byits own flash only, basically (unless the
    exposure time on one of them is much longer), based on the experiments I did
    today. I would also expect the processing times are the same but the reaction time
    from the remote button press seems to vary. I also tried the two-second delay
    before remote activation. You could hear that the beeps were out of sync.

    It is better to use just one flash because then the light source is at least constant,
    leading to better correspondence in the recorded images, and easier feature
    detection.
     

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