China Balls in Daylight

Pete Wallington · November 25, 2011

Interesting request from director, I wonder if you can help me a) check my maths and B ) come up with options...

Shot is a typical beach scene, looking slightly down on the beach and edge of the sea. Girl walks/dances on beach amongst 20 or so China Balls.

We're shooting Kodak 5207 (250D).

We're shooting during the day time, in a warm sunny part of the world.

The director wants to know if we can get the china balls to show (as lit).

My answer

- No.

My maths

- Sunny 16 rule suggests at 250ASA and 1/250th, middle grey is around F/16

We're shooting at 25fps, so 1/50th, therefore stop down by 2 stops to compensate = f/32. Key is f/32

So assuming the sand is middle grey, I figure the china balls would need to expose at least 1 stop over key, so f/64. (or more?)

I have a 12" china ball here with a 200W bulb in it. At 20ft it gives a spot meter reading of f/32 (ie - at key). So with a 400w bulb, it would probably get to around f/64.

However, I very much doubt that sand will be middle grey. I imagine it will be light orange, if not white, and therefore at least 1 if not 2 or more stops over key, in which case the china balls would need to also be an extra 1 or 2 or more stops brighter - 800, 1600, or 3200W bulbs.....

Does this sound like sensible rationale?

I guess the basic question is, how bright does a light source need to be to be visibly bright in daylight?

Ben Brahem Ziryab · November 27, 2011

Not that I have an answer to your question, but you'll need to consider the reflectivity of the sand as well in your exposure calculation. Also, I do not understand why you need the china balls in the first place if you're shooting under bright sunlight? Why not use a overhead griffolyn to fill in the shadows or a solid black to create negative fill/give it more contrast.

David Desio · November 27, 2011

Sounds like he wants the china balls to play in the shot, like The Prestige...no? Don't have an answer other than going up in power for the balls and shooting during a time of day other than noon. Maybe 4 in the after noon?

Matt Read · November 28, 2011

The best way to check your math will be to just do a test, even if that just means shooting a still on a SLR. It won't show you exactly how it will look on film, but at least that way you'll know if It's within the realm of possibility.

Matt Read · November 28, 2011

Also, your math looks right, but you should still test to be sure.

Martin Hong · December 2, 2011

In order to make the china balls to look right in bright daylight you need a very high output light source.. is gonna be a challenge.. But my question is.. why in bright daylight? I was imagining the scene shot during the sunset.... would look better and be easier for you to control.. just you will have little time to have everything done.

Dane Cannon · December 2, 2011

Okay, I know that practically this is not something you would want to do, but if it were just a single china ball -- would you be able to use something like this HMI ballast bulb combo? I've heard of it being done before.