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DImmers? Buy and/or make? Ideas?


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#1 Frank McKeown

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Posted 14 January 2012 - 02:32 PM

Hello,

Have a couple light kits, Arri kit and Lowel Rifa soft light kit. I'd like to get some portable, (ie, not too heavy) dimmers for these lights which are anywhere from 300 to 1K and tungsten-halogen but I'm also considering getting fluorescent bulbs inserts on the Rifas as well.

Does anyone have any recommendations for dimmer switches? Good places to by? Or ways to make your own? Especially regarding the possible switching between tungsten and fluorescents....

Thanks so much for any info!
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#2 Phil Rhodes

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Posted 14 January 2012 - 04:00 PM

You can't (usually, reliably) dim fluorescents externally to the ballast; dimming is usually a built-in feature. You can buy dimmable ballasts quite straightforwardly which take an 0-10V input and can be dimmed with nothing more than a variable resistor and a bit of ingenuity, but you can't use external dimmers as you would with tungsten. And no matter what anyone tells you, nobody, including Kino Flo or any other expensive manufacturer, can dim a fluorescent all the way down to zero, or without it swinging from yellowish to purplish as it gets dimmer. Also, dimmable fluorescent ballasts are up to several times the cost of the most expensive electronic ballasts.

You can use triac dimmers as used in home interior lighting to dim tungsten, but the ratings are pretty conservative, usually under 500W for the wall mount types.

Bigger triac dimmers, up to a kilowatt or so, are available from stage and event lighting suppliers, but they are not trivially cheap. I have a pair of very old-school SCR (or thyristor) based dimmer units from an old Rank Strand dimmer rack which I'm trying to get working, but they're a pain to run in the absence of their original support electronics. Older types like this can also cause significant radio-frequency interference and interference on the mains supply itself, if used in large numbers. The same is true of homebrew designs which lack the suppression and snubbing circuitry of the latest commercial products. In any case, big triacs are expensive just as discrete electronic components, as anyone who's attempted to repair an old dimmer will know. The work involved in building the rest of the low-cost circuitry around an expensive off the shelf triac component may make a homebrew design unappealing from a cost/time/benefit point of view.

It is sometimes possible to dim certain types of fluorescent ballast with a suitably suppressed and protected triac dimmer. Usually this requires an iron ballasted fluorescent, which will produce light at the mains frequency, and this may be a problem from a camera point of view. The dimmer should be explicitly specified to dim fluorescent tubes, as designs that do not anticipate this use can be damaged by high-voltage transients produced by an iron ballast. The colour output of the tube will alter wildly and there may be unpleasant flicker or strobe effects at low power. It's not a good approach.

P
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#3 Dane Cannon

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Posted 15 January 2012 - 06:25 PM

I've made several of my own and they work fine for lower wattage lights. I bet there's even a youtube video that shows you how to do it with parts from Home Depot. Watch out for buzz if you're capturing sound. True film dimmers don't have that problem. Also, be aware that dimming a tungsten light makes it warmer in color. Sometimes that's a plus though.
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#4 Dane Cannon

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Posted 15 January 2012 - 06:31 PM

Another option that I've seen quite a bit...
http://www.harborfre..._source=linking
Do a quick search on DVXuser in the DIY forum and I bet you find loads of stuff.
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#5 timHealy

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Posted 25 January 2012 - 06:50 AM

I recently bought a bunch of 1k dimmers from Film Tools for about 110 bucks each: http://www.filmtools...watrotdial.html

Having built them on my own before, it was easier and faster just to buy them than build them myself. When you factor the price of the parts and the amount of time to build a similiar one yourself, you would not really be saving anything.

Best

Tim

Edited by timHealy, 25 January 2012 - 06:51 AM.

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