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07/17/2005 08:25:51 PM · #1 |
I am hoping some techie or DIYer amoung the DPC crowd can enlighten me some. I assisted at a wedding yesterday and the photog had some $4900 in lighting equipment...I was wondering how hard it would be to build a flash unit...one can buy a flash bulb, no problem, and probably a socket too. batteries...lead acid or i have read abot using R/C car batteries. In between is a big capacitor I think, and a var resistor or potentiometer to adjust flash duration. THese components should not cost $1000...
I'm still wondering why batt packs run $250-500!
Any thoughts or links that would assist me in my understanding - can this be done for cheap or not?
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07/17/2005 08:29:36 PM · #2 |
why would you want to build a flash? just curious
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07/17/2005 08:47:01 PM · #3 |
um those big cap's can be dangerous be careful some can hold a charge for years!
also triggering a homemade flash with your flash shoe might put some serious current back to your camera. that wouldn't be much fun. |
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07/17/2005 08:54:37 PM · #4 |
| There is a charging circuit that converts the low battery voltage to high voltage to store in the cap. Thats what makes the noise when it chrages. It should be fairly easy to build however that amount of energy can kill you quickly. |
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07/18/2005 01:01:25 AM · #5 |
Why? Hopefully to save money. A flash tube is $50. A flash head can be had for $230 or less - just add the power pack. Unfortunately the power pack is where the money is- $500-700.
I have no plan to fire it off my hot shoe.
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07/18/2005 05:34:57 AM · #6 |
Do you know much about electronics already? or are you starting from scratch?
Mandatory warning: I'm qualified to electrify myself and my loved ones, if you follow my suggestions, you're on your own..
The theory is pretty simple, and you will be able to find circuits for 'disco' strobes on the net and in hobby mags that can be modified to some extent.
The major difference between disco type strobes and photo strobes are that photo strobes have more punch (higher voltage/more caps) and are single-shot, so they don't have to fire at 10Hz, and therefore the charging circuit isn't a sledgehammer..
The flash output/duration is set by accurately controling the charge voltage in the caps. The higher the charge voltage the longer the flash, the 'brighter' the light.
You'll see commercial flash units specifying 'charge dump' and 'auto charge dump' which are units that will discharge their caps down to the set voltage/exposure when you wind down the setting, without having to fire the flash. A thyristor + big resistor and a comprator with a small hysteresis 'gap' over the charging circuit will give you that.
I built some very crude low power strobes using an ETI disco design years ago, which worked OK, although it wasn't very repeatable exposure wise as the comparator I used had a fair bit of temperature drift. Also my vivitar 285's were almost as powerful, although being mains powered was a huge advantage.
I did my modelling lights via dual-track pots and hacking some mains lights dimmers, and used an opto-isolated input to trigger the strobe allowing me to safely use PC connectors, and give a lower (12V at the time) sync voltage.
For casings I used PVC pipe about 150mm in diameter, and used pipe end-caps for the ends. They looked pretty tacky, but did the job.
I took a serious look at making my own photo strobes again last year, and decided I'd just save my pennies and get some decent ones when I can afford it. I get by with my old 285's, and a nikon SB24 in the mean time, and modern monolights are so much better packaged than I would get if I did a DIY job anyway, and have some nice features if you spend enough $.
If you're just wanting to 'get started' with small scale portrait lighting, a couple of second hand vivtar 285HV's off ebay and some white umbrellas will see you a long way...
What are you wanting to photograph?
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07/18/2005 10:19:19 AM · #7 |
MHmmm...photograaph...
I likse the idea of an open bulb flash. All i see are lumedyne and quantum, and they are not cheap. I think vivitar might have a high end unit as well.
I suppsoe AB800 monolights would work, and for studio work they are my first choice. Not sure how they would work on-location run from a battery (have to check on this idea,but too busy today)
As to flash function - one can set teh duration of flash up front, of course. Your explanation and monolights work like this.
how is it done with a sensor (auto thyristor is a what?) or TTL?- I mean the cap has to be fully charged as you might need a full blast,but then TTL or light reading during the flash cuts the flash blast off in mid flash, right?
What determines the amount of light output - bulb, cap or ??
The wedding photog i assisted has 2 regular lumedyne units, and the one i carried and on her bracket were lumedyne heads 9they said so) but were glued to Vivitar 283 flashguns - they said so on them. The auto-thyristor was used for 'adjustment'. Perhaps I can get some used 283s and I saw 200ws or so open bulb flash heads for about $110 at b&w...just add a battery, right?
I have an old GN60 or so flashgun that is low power and high trigger so i do not use it..it could be my donor circuitry...
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07/18/2005 12:27:06 PM · #8 |
this is a excellent place to start reading up on flashes & strobes--
SAMS Strobe/Flash FAQ
I built one from diagram(s) from these pages - I used motor start caps (350V) and a radio shack strobe bulb -- hand wound the trigger coil
though -no way- would i ever ever ever attach this to a digital camera - the trigger voltage was +200v (as bad as a old 283)
ttl & thyristor is a squelch feedback from the camera(or flash sensor) to shorten the duration of the light pulse (dumping the cap. current rather than alloowing it all to pass through the light)
the light output is determined by , bulb design, voltage, inrush current
one of the problems faced with DIY is the FLASH caps have very low internal resistance which makes them very expencive (for the big ones)
another problem is eff. of the battery to highfreq. cap charging circuits
(this will change the time between consecutive flashes)
even internal battery resistance will cause lots of headaches ..
easier to buy used & hack than DIY
(but more fun have burn marks on your hand & be tossed across the room if you DIY ;)
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10/13/2006 02:07:29 AM · #9 |
Take a look at Strobist . You can find a lot of things there, about how to use of everyday, small, shoe-mount flashes like big strobes.
A lot of examples there. I found it very helpful. |
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10/13/2006 02:11:31 AM · #10 |
Originally posted by macox:
also triggering a homemade flash with your flash shoe might put some serious current back to your camera. that wouldn't be much fun. |
Yeah, I'd definitely go for an optical isolation circuit.
and yes a large cap can kill you a relatively small one can leave a nasty burn.
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10/13/2006 03:59:47 AM · #11 |
I put together a DIY power pack to power my strobes, essentially the same as the Alien Bees Vagabond. I bought a 300W true sine wave inverter, grabbed some 12V 5ah batteries from work (wired parallel in pairs to get 10ah), bought a pair of 12V chargers, and picked up cables and quick disconnects to wire everything together. It all fit in a generic toolbox, and it cost me less than half of what the 300W Vagabond goes for.
In the end I got tired of lugging everything around (not exactly the most compact setup with the toolbox and 2 strobes). I picked up a Visatec Litepac for cheap on ebay, and it's a lot more convenient working with.
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