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Author Topic: slave strobes fire "early" or "late"  (Read 2094 times)

Offline ghostgeek

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slave strobes fire "early" or "late"
« on: May 08, 2015, 04:44:47 AM »
Hi folks,

New member here, though I've owned a pair of T2i's for about 5 years now (has it really been that long?)

I'm working on a photography project, and I cannot make heads or tails of this problem.

My camera's are both running the latest 1.0.9 firmware.  I'm also running Magic Lantern on it, with the latest nightly build from April 19.

I purchased a set of inexpensive "slave" strobes off of ebay.  These are the type that do not have a sync cable, but rather "look" for another flash to trigger them - in this case, the camera's built-in flash.

I cannot for the life of me seem to get them to fall in sync with the camera's built in flash.  They seem to be firing  either "early" or "late."

I've played with various ISO, shutter and f stops.  Setting the flash to fire in the 1st and 2nd curtain.  Nothing normally seems to work.

The only way I have been able to get it to work is using the "mirror lock" function within Magic Lantern.  With this feature engaged, pressing the shutter release swings the mirror out of the way.  Pressing it a second time takes the image.  This method works, however the flash fires both times - when the shutter release is pressed the first time,  and then the second time.  This isn't ideal, as I have to wait for the strobes to recharge after the first trigger.

Does anyone have any ideas on how to rectify this problem?  Thanks so much for your insight.

Offline AndyCivil

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Re: slave strobes fire "early" or "late"
« Reply #1 on: May 08, 2015, 08:38:33 AM »
Heh - I love those little slave flash units. I put them inside makeshift soft boxes to increase illumination. I find that they need the "S2" setting, to fire correctly. (Fire on the second flash.)

There are two things that could be causing it; one is the Red-Eye correction, I have mine turned off. The other is the pre-flash for autofocus. I suspect that it's the latter that is causing your particular problem, because you say you can fix it with mirror lockup: when the mirror is locked up, it can't use the phase-detection quick focusing in the pentamirror, because it's out of the loop.

Darned if I can find a control for that pre-flash, though. Maybe you can't disable it? In fact, perhaps that's why I need S2 - the first one is the focus/metering flash. Try turning off the red-eye and see if that cures it for you?

Offline Craig

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Re: slave strobes fire "early" or "late"
« Reply #2 on: May 08, 2015, 09:25:44 AM »
I would agree with Andy. I would think the pre-flash is triggering your strobes. This is a very common problem.
6D, T2i, Canon 600EX, 430EXII, and some other stuff my wife doesn't know about.

Offline ghostgeek

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Re: slave strobes fire "early" or "late"
« Reply #3 on: May 08, 2015, 12:39:15 PM »
Hello Andy and Craig,

Thanks for the quick reply.

OK here is what I determined.

The problem is indeed that "preflash" that is firing first.  I determined this by using a long 5 second exposure.  On a quick exposure, the duel flashes are so close together, that they aren't obvious, but on a long exposure, it's apparent that the flash is firing twice. When the slaves are triggered on the second curtain flash, the image gets exposed, but this only works on a long exposure, as the slaves need a few seconds to recharge.

What's weird, is that I seem unable to override that preflash.  I have put the camera into manual focus, and I have disabled the red eye reduction settings.  But every time I take a photo, the flash fires twice.  Even in "2nd curtain" mode for the flash.

Thinking this might be a glitch with Magic Lantern, I removed the SD card that ML is installed on, and even re installed the Canon issued 1.0.9 firmware.  The problem stil persists.

This is happening on BOTH of my T2i's.  I can't figure this out for the life of me.

Offline Craig

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Re: slave strobes fire "early" or "late"
« Reply #4 on: May 08, 2015, 03:11:28 PM »
Are you shooting in manual mode. If not, try that. I don't see why the camera would need a preflash if in completely manual mode. That's how you should be shooting with flash. Shutter, aperture and ISO all manual.
6D, T2i, Canon 600EX, 430EXII, and some other stuff my wife doesn't know about.

Offline AndyCivil

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Re: slave strobes fire "early" or "late"
« Reply #5 on: May 08, 2015, 05:31:20 PM »
Most of us fix this by setting the slave to "S2" meaning to fire on the second flash. Does yours not have this choice?

Offline ghostgeek

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Re: slave strobes fire "early" or "late"
« Reply #6 on: May 09, 2015, 02:05:17 AM »
Hi again guys...

Craig - yes, I'm shooting in manual mode.

Andy - no.  These are ultra cheap optical slave strobes (four for $30 with shipping on ebay.  LOL)  There are absolutely NO settings for these.  You screw them into a standard light bulb socket.  They charge up, and when they detect another flash, they fire.

I've been doing a little more digging, and apparently the preflash on the 550D / T2i is NOT something you can just turn off.  The camera's built-in flash is stuck in E-TTL.  The only practical way to trigger dumb optical slaves (other than the mirror lock that I previously described) is to use the lock exposure FEL.  In other words, manually fire the pre flash using the * button in advance of the main flash.  Then give the slaves (and of course the built-in camera flash) 10 seconds or so to recharge.

I'm very surprised that this is not something that can be overridden in Magic Lantern.  It would appear this "feature" is either a bone-headed oversight, OR how Canon gets you to invest in expensive "hot shoe" strobes.   >:(

Well, unless you guys have any other ideas, I guess this is how it's going to be for the time being, until I have the $$ to invest in a hot shoe strobe.

Thanks again!
« Last Edit: May 09, 2015, 02:42:23 AM by ghostgeek »

Offline Craig

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Re: slave strobes fire "early" or "late"
« Reply #7 on: May 09, 2015, 11:02:46 AM »

Well, unless you guys have any other ideas

Buy some radio triggers  ;).  Yongnuo has a good product line at reasonable prices.
6D, T2i, Canon 600EX, 430EXII, and some other stuff my wife doesn't know about.

Offline AndyCivil

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Re: slave strobes fire "early" or "late"
« Reply #8 on: May 09, 2015, 11:03:20 AM »
Dang, yes I think you might have been a bit TOO cheapskate there... These are the ones I have:
http://www.amazon.com/Neewer-Digital-Slave-Bracket-Cameras/dp/B002X3VBFK
you can see on the Amazon site the back view and the slider to select S2 - it sounds like yours are stuck on S1.

Offline ghostgeek

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Re: slave strobes fire "early" or "late"
« Reply #9 on: May 09, 2015, 12:07:22 PM »
@craig, unfortunately, these flash bulbs are only optically triggered.  There is no input for a wired trigger, so a radio trigger wont help.  :(

@andy, I think you're right on the cheapsake part.  LOL  What I like about these is that I can screw them into ANY standard light socket.  I can use a $7 clamp lamp fixture from Home Depot, and the hood works nicely for controlling the spill.  I'm trying to use them for a high key shoot, and they actually work nicely for blowing out the white background.

http://www.ebay.com/itm/281647191119

There IS an upgrade that is a few dollars more, and DOES have the input for an external trigger.  Sure am wishing I'd bucked up and gotten one of those now!  I actually might end up doing that anyways.

Just so I know what I'm buying, at the very least, I need a strobe that mounts on the camera's hot shoe, correct?  I note that some strobes are TTL triggered, E-TTL, E-TTL II...  it's all very confusing to me.  But to clarify, will ANY inexpensive strobe that I connect to the hotshoe (A) get triggered by the camera when I take a photo?  and most importantly (B) NOT fire a "preflash?"   

If a cheap hotshoe strobe will ONLY trigger one flash, then I'm golden, as that will trigger the optical slaves when they need to fire.  But if it's going to emulate the onboard flash, then I'm still screwed and back to square one.  I'm on a limited budget (as I'm sure you can tell!) and just want to be sure I'm not throwing away more money.

Thanks again guys - you've both been a huge help!

Offline Craig

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Re: slave strobes fire "early" or "late"
« Reply #10 on: May 09, 2015, 01:14:34 PM »
From another web site.     

 "your camera has no idea the off camera flash even exists, since it is not in communication with it. If the flash mode on the camera is set to E-TTL then the camera is assuming the built-in flash is the only one and is going to fire a pre-flash to meter the reflectivity of the subject. Unfortunately, page 148 of the T2i Instruction Manual indicates that E-TTL is the only option with the built-in flash. To select Manual flash you must have a compatible external Speedlight attached to the T2i"
6D, T2i, Canon 600EX, 430EXII, and some other stuff my wife doesn't know about.

Offline AndyCivil

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Re: slave strobes fire "early" or "late"
« Reply #11 on: May 09, 2015, 01:58:56 PM »
I'm not sure I agree with the statement "your camera has no idea the off camera flash even exists". If it's plugged in to the hotshoe, then it absolutely knows it's there. Try pushing the "flash" button, and note how the pop-up does NOT flip up into the external one  ;)

I have discovered, playing with my Neewer flash units, that if you have a "dumb"* flash unit in your hotshoe, then it fires only once (at the beginning of the exposure).

*(By 'dumb', I mean that it has only the central electrode for firing - there's no data communication like a speedlite.)

I was able to 'see' (meaning that it flashed inside the exposure time) one of my flash units while set to S1, by plugging another one into the hotshoe.

I suggest you buy just one (if you're cheap) of those Neewer units. You'll then have two options.

1: if you put the Neewer on your camera ('Normal' mode) then it will correctly trigger your set of four eBay units.

2: if you set the Neewer to slave (S2 and "Slave on") then you can put that one remotely in a soft box, or to light the background, ceiling whatever. (But in this case your eBay slaves are useless, as you found.)

Craig will have to tell you about triggers—I confess I haven't played with them!