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M18 or 4K HMI to light pool for underwater shoot


Pascal Combes-Knoke
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Hi,

I'm about to shoot a low budget music video. I will be SCUBA diving with a 5D mrk iii, at the bottom of an 8-9 foot pool. Talent will only be a couple feet underwater. I will line the pool with black cloth to make it seem like a large lake.

Can i get enough light out of an M18 or do I need a 4kHMI? I'm not sure how much light is lost bouncing off the top of the water and how much the water itself will diffuse the light...

 

Secondarily, should I black the bottom of the pool to reduce fill to get a nice ratio?

 

I hope some please on this forum have experience shooting underwater.....

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Haha, I came here to ask exactly the same question for exactly the same reason! I'd also appreciate any suggestions as to the best material to 'black' a pool with - Tarpaulin? Cotton?

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As a DIT, I'd recommend 640 ISO on the mk3. Due to the electronic processing, perfect multiples of 160 are cleaner, way cleaner than any other ISOs. Like... 640 is cleaner than 500 and so on.

As a budding DP... I've never done underwater, though I'd get the m40 and give myself all that extra leeway. It´d allow you to bounce on silver if you find it too hard, still keep a reasonable base stop and a better falloff. It'd also raise the shadows without looking fake.

I do wonder how water, and whatever particles one throws in, create fill. Very interesting theme.

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M18 will get in there but wont have much spread. But its house power (depends where you is) so thats a major plus.

Depends what lighting there is above pool too. Youd normally do an 18 or 6 into bounce above pool and an 18 or 6 into the pool as beam.

 

Kenfield, borrow an underwater black off a grip or PanaSux. A black tarp might work but expensive to buy for a one off gag. Ya gotta throw some shotbags on the bottom so make sure they aint gonna bleed into the pool. Dry it on a 12ft bar before you give it back.

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I shot pickups for a movie last year in a similar situation. We had underwater blacks from the Rag Place in LA. Camera was either a 5D or 7D set at 800 iso, I can't remember exactly. We shot at night, with talent just a couple of feet below the surface. The whole setup was lit with 500w tungsten work lamps from Home Depot. Worked fine.

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Seems like such a waste of time and money, no one watching is gonna know or care if you blacked the pool.

 

We'll be blacking the background, you'd absolutely know the difference between that and pool tiles a couple of meters behind the talent.

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Ahso.

 

Underwater black ive used is like black side of ultrabounce, so as long as its soft its good.

 

In saying that, id probably put my 12by griffloyn in a pool as itd dry fine. Sadly i think ultrabounce wouldnt like the chemicals, but yeah if you could get griffloyn that might be an easy way.

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Hi, I'm about to shoot a low budget music video. I will be SCUBA diving with a 5D mrk iii, at the bottom of an 8-9 foot pool. Talent will only be a couple feet underwater.

 

However you decide to shoot the pool scene be sure to use GFCIs on all the cables supplying your lights – whatever size they happen to be. After that NYU student was electrocuted I am surprised safety is not at the forefront of this thread. GFCIs are a must when working within 25’ of water in order to avoid someone taking a potentially lethal shock. If you stick with smaller quartz lights, you will be fine with the hardware store variety of GFCI cords. But, if you use HMIs, or even Kinos, you will need film style GFCIs, like Shock Blocks, that are specifically designed for motion picture lights. To prevent the nuisance tripping that electronic Kino & HMI ballasts can cause with standard GFCIs, film style GFCIs sense on an "Inverse Time Curve." And, to deal with the harmonics that non-PFC Kino & HMI ballasts kick back into the power stream (that will cause other GFCIs to trip), film style GFCIs include a harmonic filter with a frequency response up to 120 hz. 3rd harmonics are attenuated by 50%, and by 500 Hz are down to 20%. Attenuated by the filter, the harmonics generated by dirty loads such as non-PFC Kino & HMI ballasts, pose less of a problem.

 

 

SB_Location_Still.jpg

A single 100A GFCI "Shock Block" can provide ground fault protection on wet

locations for the entire distro system of a Honda 6500 portable generator

when used in-line with a Step-Down Transformer/Distro.

One problem with Shock Blocks is that they don’t come smaller than 100Amps. If you can’t rent a tow generator with a distro box with 100A pockets, the next best thing is a step-down transformer like the 60A Full Power Transformer/Distro we make for our modified 7500W Honda EU6500is generator. A transformer will step down the 240V output of a portable gas generator to a single 60A 120V circuit that you can put a Shock Block on.

 

A 100A GFCI used inline with a transformer can provide safe and secure ground fault protection for an entire distribution system consisting of Bates Extensions, Splitters, and Break-Outs to Edisons – eliminating the need for hardware store 20A GFCIs that are not designed to be used with harmonic generating loads like non-PFC HMI & Kino Ballast, & LED Power Supplies. Used in-line with transformer/, a 100A Shock Block will provide a larger GFCI protected circuit than is commonly available in homes. In fact, it enables the operation of even 4k HMIs on portable generators with GFCI protection.

 

For more detailed information on using Shock Blocks to provide Ground Fault protection with portable Honda generators, I would suggest you read a curriculum I developed for IATSE Local 481 on GFCIs and grounding. You can find it online at http://www.screenlightandgrip.com/html/481_GFCI_Workshop.html

 

Guy Holt, Gaffer, ScreenLight & Grip, Lightng & Grip Rental in Boston

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Thats for all the great advice everyone

 

I shot pickups for a movie last year in a similar situation. We had underwater blacks from the Rag Place in LA. Camera was either a 5D or 7D set at 800 iso, I can't remember exactly. We shot at night, with talent just a couple of feet below the surface. The whole setup was lit with 500w tungsten work lamps from Home Depot. Worked fine.

@stuart do you have the final product online anywhere?

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