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6 Days Ago - 1 Like   #16
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The RF60 has a multi flash mode... You literally tell it X flashes at Y hertz. I haven't measured if it's actually consistent between strobes, this is too picky for me at this point!

I played around with this a bit tonight. It's too cold outside for great accuracy, but fun was definitely had.





6 Days Ago   #17
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QuoteOriginally posted by AstroDave Quote
How you gonna do that?

I doubt your flashes can cycle that fast at anywhere near adequate power.

If you want to do multiple flashes at small intervals, you probably need some kind of sequencer.

That could actually be very simple and straightforward, though. Is your engineer friend good with simple digital circuits? It would be trivial with a couple of IC chips (and maybe a couple of transistors to actually fire the flashes) to create delays of a few milliseconds (and shorter or longer) between several trigger pulses.

I donít know what the capabilities of your Cactus units are, but here are some relevant data from my Pentax AF540-FGZ (original version).

First, hereís the light intensity as a function of time for the flash set to 1/32 power. The total flash duration is about 100 microseconds. For more discussion of effective flash duration at various power levels, see my measurements of the AF540 from a while ago (Flash Duration Measurements - AF-540FGZ - PentaxForums.com). From what I have learned from the Web, virtually all modern electronic flashes have nearly identical time-versus-intensity profiles. It is just the maximum amplitude that differs as a function of specific flash model.




I have not tried to measure the recovery time after such brief flashes - it seems pretty fast, but I rather doubt it is fast enough for 100 Hz flashing.

The AF540 does have a modeling pulsing flash mode, though. Hereís what the first few pulses of that look like - short, low power flashes every 20 milliseconds (50 hz flash rate) for a second. Note that the sensitivity level for these pulses is 1/10 that of the 1/32 power flash shown above - so not a lot of light output.




And hereís a close-up of the time profile of one of those pulses - quite short (even shorter than the 1/32 power level).




Maybe if you crank your sensitivity up, you can take advantage of a similar mode if your Cactus has that. Otherwise, as noted above, I think you will need a sequencer to get multiple images of your arrows at small time intervals by firing separate flashes.

Good luck! Sounds like fun (and have some sponges handy!)
I read your post again, informative stuff! My friend is an electrical engineer but I donít think Iíll be able to convince them to wire up a test circuit.

Iím going to do some more practical tests with the multi strobe feature, see how it goes.

Hilariously we tried to shoot a pumpkin with a crossbow bolt tonight. The bolt went clear through the pumpkin, no explosion, no flash!
5 Days Ago - 1 Like   #18
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QuoteOriginally posted by bobbotron Quote
This v6 trigger is set to TX, linked via a 3.5mm cable.
As @BrianR has pointed out, you don't need that intermediate V6 in a TX role.

The LV5 sensor can trigger another receiver (and hence camera) or flash via radio.
The only snag you may potentially hit is an incompatibility between the LV5 and the RF60 firmware versions. Potentially, you might need to downgrade the RF60 firmware version to an earlier one, so that the RF60 can still talk the older flash protocol used by the LV5 sensor.

BTW, if you can place the LV5 sensor near the camera/flash, you could even fire the camera/flash directly without involving radio communication.

QuoteOriginally posted by bobbotron Quote
Cactus flash, set to manual mode multi flash mode, attached to a V6 trigger in receiver mode (I've found this is a lot more reliable for whatever reason)
Again, the use of an additional V6 unit in a RX role is not necessary as your Cactus flash has a built-in radio receiver already. Currently you are using two superfluous units that only introduce lag.

If you have reliability issues with firing the flash directly from the LV5 sensor than try angling the flash body slightly differently (while compensating with the flash head). Alternatively, try using a different flash channel, making sure you go beyond five. The first five channels on the older flash protocol used on the LV5 all use the same frequency (to implement a poor man's approach to group broadcasting).

QuoteOriginally posted by bobbotron Quote
So this all works, *except* the V6 trigger only seems to trigger the K3 about once every 4th shot.
I suspect this is due to the LV5 generating a trigger signal that is too short (unless the failed trigger events are due to the camera going into a sleep mode from which it has to sloooowly wake up before it can respond to a trigger event).
Are you running the LV5 sensor in "Multi" mode?
If so, switch it to "Single" mode and with a bit of luck the extra trigger signal padding that is then used will be sufficient to reliably fire your camera.

BTW, a long time ago I wrote a review about the LV5 that you may find useful. I only tested the version without the useful "delay" and "freeze" controls, but it is unlikely that you'll need these features in your application (except perhaps the "freeze" control if you are suffering from too many subsequent trigger events).

QuoteOriginally posted by photoptimist Quote
Wouldn't you trigger the K-3 first with some longish shutter time so the shutter is fully open when the strobes fire?
That is one approach and most recommended if the camera lag time is either
  1. too long to allow capturing an event, even when placing the "laser fence" such that it is broken long before the moving object (here the arrow) hits the scene of impact, or
  2. too variable. The camera, depending on what is currently processing internally, does not always have the exact same response time. Flashes are not only significantly faster to respond but also with much less variability.

@bobbotron If you want to keep firing the camera (instead of the flash) then I would recommend to connect a V6 in RX mode to the camera in order to trigger it, and use a V6 mode in TX mode (using a different channel) on top of your camera to trigger your flash. That way, you won't have to manually achieve synchronisation between camera and flash.

However, in your application it seems more promising to reduce the ambient light to a level that allows a longer exposure so that the flash will decide the exact point of exposure, not the camera.

Last edited by Class A; 5 Days Ago at 09:48 AM.
5 Days Ago   #19
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Thanks for weighing in! I will try to downgrade at some point, the LV5 definitely does NOT trigger any of my V6 equipment at the moment. I have tried hard to get it to work, though have not tried a protocol downgrade. Which is fine, I've been triggering the flash right off the laser sensor via a cable.


I think you're correct about the signal from the LV5 being too "short". It is in single mode, even the cactus RF60 flash will 100% of the time consider it a event, whereas if I'm driving a V6 trigger from it, in TX mode, it rarely considers it an event. This is all fine, I have enough of the components to drive it in such a way that works well.

I'm off trying to get the setup to trigger the camera, using a black background works well. Definitely need more practice experimenting with things.

I'm curious if you know how much of a "delay" the wireless signal introduces? I was wondering about this, how much time it takes for one "message" from transceiver to receiver. If it's super fast, I could see using an RF60 as a master, to then fire off a flash into the air and trigger my 2nd flash.


QuoteOriginally posted by Class A Quote
As @BrianR has pointed out, you don't need that intermediate V6 in a TX role.

The LV5 sensor can trigger another receiver (and hence camera) or flash via radio.
The only snag you may potentially hit is an incompatibility between the LV5 and the RF60 firmware versions. Potentially, you might need to downgrade the RF60 firmware version to an earlier one, so that the RF60 can still talk the older flash protocol used by the LV5 sensor.

BTW, if you can place the LV5 sensor near the camera/flash, you could even fire the camera/flash directly without involving radio communication.


Again, the use of an additional V6 unit in a RX role is not necessary as your Cactus flash has a built-in radio receiver already. Currently you are using two superfluous units that only introduce lag.

If you have reliability issues with firing the flash directly from the LV5 sensor than try angling the flash body slightly differently (while compensating with the flash head). Alternatively, try using a different flash channel, making sure you go beyond five. The first five channels on the older flash protocol used on the LV5 all use the same frequency (to implement a poor man's approach to group broadcasting).


I suspect this is due to the LV5 generating a trigger signal that is too short (unless the failed trigger events are due to the camera going into a sleep mode from which it has to sloooowly wake up before it can respond to a trigger event).
Are you running the LV5 sensor in "Multi" mode?
If so, switch it to "Single" mode and with a bit of luck the extra trigger signal padding that is then used will be sufficient to reliably fire your camera.

BTW, a long time ago I wrote a review about the LV5 that you may find useful. I only tested the version without the useful "delay" and "freeze" controls, but it is unlikely that you'll need these features in your application (except perhaps the "freeze" control if you are suffering from too many subsequent trigger events).


That is one approach and most recommended if the camera lag time is either
  1. too long to allow capturing an event, even when placing the "laser fence" such that it is broken long before the moving object (here the arrow) hits the scene of impact, or
  2. too variable. The camera, depending on what is currently processing internally, does not always have the exact same response time. Flashes are not only significantly faster to respond but also with much less variability.

@bobbotron If you want to keep firing the camera (instead of the flash) then I would recommend to connect a V6 in RX mode to the camera in order to trigger it, and use a V6 mode in TX mode (using a different channel) on top of your camera to trigger your flash. That way, you won't have to manually achieve synchronisation between camera and flash.

However, in your application it seems more promising to reduce the ambient light to a level that allows a longer exposure so that the flash will decide the exact point of exposure, not the camera.


4 Days Ago   #20
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QuoteOriginally posted by bobbotron Quote
I will try to downgrade at some point, the LV5 definitely does NOT trigger any of my V6 equipment at the moment.
Too bad that it doesn't work out of the box. It seems you are running a firmware version on the V6 that made it compatible with the V6II but unfortunately meant that the V5/LV5 side could not longer be supported. A downgrade (or sidegrade) to a firmware using the V5/LV5 protocol should do the trick.

QuoteOriginally posted by bobbotron Quote
I think you're correct about the signal from the LV5 being too "short".
It is unfortunate though that this happens in single mode as well. As I said, in this mode, the LV5 artificially prolongs the event duration in order to give most cameras sufficient time to recognise the trigger event, even if the original sensed event is way too short. It's been a long time and I never used the "delay" and "freeze" features extensively, but potentially you can increase the trigger duration of the LV5 sensor by setting a longish freeze period (something over "150ms" should be plenty). Worth a try, but as you say you currently have a setup that works, so you'll only need to tinker some more if you want to use other configurations.

QuoteOriginally posted by bobbotron Quote
I'm curious if you know how much of a "delay" the wireless signal introduces?
Sorry, I don't. For most applications the delay is negligible. For very fast moving objects, I would expect to see a noticeable difference in distance travelled, though. However, most of the time you can just compensate for that by moving the "laser fence" more towards the origin of travel.

QuoteOriginally posted by bobbotron Quote
If it's super fast, I could see using an RF60 as a master, to then fire off a flash into the air and trigger my 2nd flash.
Whether you are using radio communication or optical triggering, I think in both cases you'd get good results.
The flash pulses themselves have a duration (which is much larger than the delay, at least near full power) so you'll get an overlay of two exposures at different times but they'll be very much smeared together because of the relatively long flash pulses.

Firing all flashes at the same time by one source should be more accurate but I wonder how much of a visible difference would be observable.
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