[bobbotron]

I have a cactus laser trigger and I'm trying to work out the kinks in it. I'm getting there, could use some tips and advice. The end goal is to do strobe (multi flash) photos of an arrow passing through a water balloon.

Current setup
Laser triggers, cactus v6 trigger set up with the emitter. This v6 trigger is set to TX, linked via a 3.5mm cable.

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)

Cactus trigger on my K3, set to rx mode, linked via trigger cable.


The issue

So this all works, *except* the V6 trigger only seems to trigger the K3 about once every 4th shot. It's very weird. I turned off live replay on the K3, but it still seems to not get the signal all the time. My theory is that the flash "signal" is too short. If I manually trigger it from the V6 trigger it works every time.


All the bits

[photoptimist]

Color me confused.

Wouldn't you trigger the K-3 first with some longish shutter time so the shutter is fully open when the strobes fire?

The sequence would be:
1) trigger K-3
2) fire arrow
3) arrow breaks/reflects the laser beam
4) flashes fire
5) balloon bits and water goes everywhere while flashes fire
6) K-3 shutter closes
7) family complains about wet floor

[bobbotron]

That's my fallback order of operation, but I was hoping to do it this way so it's a fully enclosed event loop. You can put a slight delay on the cactus flash too, to ensure the shutter is open when the flash activates.

In theory you can use this to "capture" wildlife too. It does work when the k3 actually gets trigger, just kind of intermittent.


Ha, I'm going to do this outside!

[AstroDave]

You can put a slight delay on the cactus flash too, to ensure the shutter is open when the flash activates.

In the meantime, your arrow is a meter beyond the balloon.

Photoptomist is correct - you need to get the K3 ready in advance. It takes around 100 milliseconds (0.1 second) for the shutter to open/fire after you press "go" (Shutter Lag - K-3 and K-1 measurements - PentaxForums.com) Again, your arrow is way downstream.

Conversely, the flash should fire in less than 1 millisecond from triggering.

I've shot water drop splashes, and my setup opens the shutter some quarter of a second before any real action. All exposure instances are set by the flash.

I've also measure the trigger time for one flash starting another. For some really cheap flashes ($10 Neewers from Ebay), the time is ~50 microseconds or less.

[bobbotron]

Fair enough! That’s a great point.

[Mot11]

The inconsistent firing appears to be a common problem with Pentax DSLRs and high-speed triggers. I had the same issue with both the Hi-Viz and Nero triggers. In spite of trying several different strategies and a couple of different Pentax DSLRs I couldn't get consistent firing. Photooptimist's suggestion is the the way to go. Doing that I was able to get some nice water balloon burst and breaking glass. Good luck.

[bobbotron]

I'm all about using the tools in the way that makes the most sense. A friend's coming over tonight and we're going to have a go of some action photography, will post up the results.

@AstroDave, thanks for all of the insights. I mostly have Cactus flashes so I'll be running them at 1/64 or 1/128th power. I don't know if they publish their lag times, will see how it goes. I guess reducing the number of "messages" would make sense, if there's some delay between triggers etc. I have a long flash cable, was thinking trigger to flash via a cable.

[AstroDave]

I have a long flash cable, was thinking trigger to flash via a cable.

That should be fine, in terms of any added delay (typical cable propagation speeds are about 2/3 the speed of light - so a few nanoseconds for a meter of cable). And, for multiple flashes, you should be able to "t-off" to all of them from a single trigger. I'm not sure, though, whether one-in/multiple-out adapters exist for these cable types. What kind of connectors do the Cacti use?

[BrianR]

I shouldn't admit it, but I have a set of these laser triggers that I've yet to use (someone was selling a brand new set dirt cheap and who can resist bargain priced lasers?).

Doesn't the V5 laser sensor have a built in wireless transmitter that can wirelessly sync up with v5 or v6 series receivers? In other words, can't you ditch the transmitter you have the v5 laser sensor sitting on? Less things in the triggering chain means faster response.

At least with other wireless systems, having the same "fire" signal sent to a flash and a camera shutter can lead to flash&camera sync problems. If the camera and flash are tripped at the same time the flash is sometimes done before the shutter is even open. Is this not a problem? How long is your flash set to multistrobe for? When I've done remote camera & flash setups with other wireless systems I've used:

1) Tx set to channel 1 that starts the event.
2) Rx set to channel 1 that trips the camera shutter.
3) Second Tx in the cameras hot shoe set to channel 2.
3) More Rx's set to channel 2 to trigger the flashes.

I do agree with the previous advice though, my attempts at high speed flash involved a sound or laser trigger (yes I already owned a different trigger before buying the V5 set...but more lasers is never wrong) that was connected directly to a flash via a wire. The room was dark and the cameras shutter was open before things started. This minimizes lag and makes syncing your flash with your event simpler.

[bobbotron]

So I read that the V5 emitter *should* send out a wireless signal that the V6 gear will pick up, but in practice I'm not sure how to make that actually work. Setting the flash to slave mode, it doesn't get the signal when I hit test on the emitter.

@BrianR, interesting stuff. My engineer friend and I are going to have a go of it tonight, try a few different things. This is my first set of laser triggers, that's cool you have a few!

[kaseki]

Room dark, camera shutter opened, .22 cal bullet in flight detector (acoustic pressure or electric field sensing), time delay, strobe actuation, camera shutter closed, room lights on, Polaroid photo developed of bullet entering something like an apple -- is exactly how Dr. Edgerton demonstrated the process in his lab in 1960 (pre-laser) and very likely the method he used in 1940 (except for the Polaroid part), but that was before my time.

[BrianR]

So I read that the V5 emitter *should* send out a wireless signal that the V6 gear will pick up, but in practice I'm not sure how to make that actually work. Setting the flash to slave mode, it doesn't get the signal when I hit test on the emitter.

There's a channel selector on the LV5 laser sensor, make sure it matches the channel on your V6's that are in Rx mode. I think that's all you have to do (but I don't have cactus wireless receivers).

"Slave" on your flash might be the lower tech optical triggering method - the flash has a light sensor that triggers when another flash has gone off. This can be useful when ganging up multiple flashes. Some of the Cactus flashes also have built in wireless receivers that should let the LV5 trigger them directly without your V6 receiver, I'm not sure which models though. @ClassA is the Cactus guru around here, and can probably advise.

@BrianR, interesting stuff. My engineer friend and I are going to have a go of it tonight, try a few different things. This is my first set of laser triggers, that's cool you have a few!

I can't resist discount stuff - I have one of the older model miops triggers from a clearance sale. It can be triggered a few ways, laser, sound, lightning...I've used it with some success on dropping things in water or exploding water balloons.

I mostly practice photography on my own, but I've had some great times with friends photographing water splashing all over the place. Have fun!

[bobbotron]

There's a channel selector on the LV5 laser sensor, make sure it matches the channel on your V6's that are in Rx mode. I think that's all you have to do (but I don't have cactus wireless receivers).

"Slave" on your flash might be the lower tech optical triggering method - the flash has a light sensor that triggers when another flash has gone off. This can be useful when ganging up multiple flashes. Some of the Cactus flashes also have built in wireless receivers that should let the LV5 trigger them directly without your V6 receiver, I'm not sure which models though. @ClassA is the Cactus guru around here, and can probably advise.



I can't resist discount stuff - I have one of the older model miops triggers from a clearance sale. It can be triggered a few ways, laser, sound, lightning...I've used it with some success on dropping things in water or exploding water balloons.

I mostly practice photography on my own, but I've had some great times with friends photographing water splashing all over the place. Have fun!

Yeah, the RF60 triggers have a wireless trigger built in, so in theory they can pick up the signal. I'll have to play around with it more. The V5's are great at what they do, but the dial on them has unusably small numbers on them. I'll have to read the book again to figure out what RF channel `1` maps to. Triggering via a cable is simple and incredibly reliable, and fine for the trigger setup I'm planning, so might go that route.

It's interesting, I'm planning on using a crossbow that fires (in theory) at 400 feet per second. Using multi flash, with a relatively high hertz of 100, this means (if my math is right) that the bolt will travel 4 feet per flash pulse. This means that at most I'll get about 3 images captured. I have some pumpkins I plan to test this all out with as well as water balloons.


The fun thing, is that I have enough of all of the components to play around with different set ups.

[AstroDave]

Using multi flash, with a relatively high hertz of 100

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 don’t know what the capabilities of your Cactus units are, but here are some relevant data from my Pentax AF540-FGZ (original version).

First, here’s 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. Here’s 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 here’s 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!)

[BrianR]

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.

What would this do that the built in Multi-Flash mode can't? For example, my sb-80dx claims at 1/16 power that it's good for 8 flashes at 100hz, at 1/32 power it's 16 flashes, and so on. I don't have an oscilloscope to test though. Do you have a flash with this capability to test? I don't see it in the manual for the AF540*, but the new version does (according to the manual it has a setting up to 200hz).

*Does the original AF540 really not have a multi-flash mode? It feels like I should be mistaken, but I don't have one to check.

A followup since you own an oscilloscope - have you ever tested the response time of the 'dumb' slave mode? It looks like SL2 mode on your flash (page 52 of the manual) is a dumb slave that responds to other flashes. If you have a second flash you could check the delay. This is somewhat on topic here, I've slaved flashes this way off a main flash in Multi-Flash mode before and it's worked for slower moving stuff. I'm wondering if the delays are typically low enough to sync for higher speed things like bobbotron is doing.