Idea...Flash.

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cactusface

Senior Member
Hi,
this is just an idea and may have been done before. My mate like me is a keen photographer, he uses a lot of flash, now building a flash slave/trigger is easy. But modern digital cameras use a number of pre-flashes to pre-focus, exposure and reduce red-eye. He has build a slave and has to guess the number of pre -flashes and set it on a DIL switch, a bit hit and miss

Could we use the count function to count pre-flashes + main flash, on a TEST! setting, then the Picaxe would remember this (in W0/B0, etc) and fire the flash on the right count! I don't see a problem do you??
Comments welcome,
Regards
Mel.
 
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MartinM57

Moderator
The environment:
- What's the typical number of pre-flashes?
- What's the duration of the pre-flashes?
- How far apart (time) are the pre-flashes?
- Is the gap between the last pre-flash and the main flash the same as between the pre-flashes (may not need to know that)
- How coincidental does the start of the main flash and the start of the slave flash have to be?

With that understanding you might be able to come up with a solution, but:
- what sensor are you going to use that will allow counting of pre-flashes - i.e. has a quick enough response time to differentiate between them
- how is the COUNT command going to work - it just counts the number of low to high transitions in a period that you define - it terminates on the elapsed time you set, not on the number of counts

So maybe you'd have to use the PULSIN command - but that doesn't terminate until the end of the pulse - but maybe the end of the last pre-flash is a good enough trigger to fire the slave flash? If the PICAXE can do it fast enough....

...and then there's the electrical side of things in firing the slave flash, but I guess there's standard circuitry for that

So, no problems at all - just a bit more understanding needed ;)
 
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MartinM57

Moderator
Maybe more feasible to use a PIACXE-based device to count the number of pre-flashes to inform your mate what to set his DIL switches to - since if his home-made slave works (how does it work?), then none of the above complexities involved in re-designing his slave to be PICAXE-based apply
 
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MartinM57

Moderator
...and...finally...how many camera/flash combinations has your mate got? If he's only got a small number (like 1:)) then it can't be that hard to work out by trial and error what the right DIL switch settings are...

...and doesn't his camera have a sync output that only fires on the main flash starting?
 
D

Dippy

Moderator
cactusface, give your idea a go.
And maybe look at intensity too.

If none of that works then come back here and we can turn the molehill into a mountain.
 
C

cactusface

Senior Member
Idea Flash slave..

Hi Folks,
Many thanks for you replies and suggestions! Martin you worry too much, Pre-flashes 1 to 7, time between don't know how can it matter? same for their duration, the whole thing is over in a flash!! I mean about half a second? But you did pose one very interesting point. I had only thought about counting the pre-flashes, using count with say a 2 second time frame, start count, fire flash (take picture, facing unit). But what when it comes to real use, what about the first pre-flash starting the count, and firing the flash on the last count (as stored in B0/W0), pulsein might be useful. I would use a photo diode as these I think are fastest. I've seen slave units using photo-transistors, CDS and photovoltic cells, the pulse of light produces base current for a transistor which then triggers a thyristor, across which the flash lead is connected and bingo. I have no idea how many cameras or flash units my mate has, but was thinking in more general terms for others too..
Best regards
Mel
 
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