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how much wattage?

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reggie ronconi
how much wattage?
on Mar 13, 2008 at 1:47:30 am

Hi,

I need to shoot an indoor tungsten scene at around f11, using 200T color negative film. (Shutter angle 150 degrees, so speed 1/60th). My light meter seems to be telling me I will need an EV of between 16 and 17 to do this. My lights need to be maybe 8 ft, 7 ft, and if I need to use a third, 17 ft away from the subject or so. The main concern with lighting for this shoot is really the AMOUNT of light I need, because the shots are going to be filtered so I must widen the aperture significantly from the base of f11. Will three 600W lamps do it at these distances? Do I need more light than this, less light than this? (I'd be pretty much just pointing them at the subject from the points on the triangle and maybe be able to intensify the illumination with barn doors.)

Is there some sort of chart I can download somewhere that figures some of these basic relationships? I'm just trying to figure out what lights to rent without having to rent them twice.

Thanks


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Todd Terry
Re: how much wattage?
on Mar 13, 2008 at 2:30:07 am

Wow, man... that particular combo (200T, f11, 1/60th) is a very very tall order.

I'm not sure why you want that particular combination, but I'm guessing you need very deep depth of field, and also fear that faster film (500T or whatever) will give you huge grain.

It's doable, I suppose, but there's no way that three 600w instruments is going to illuminate that scene satisfactorily. If you must stick with those parameters (the film speed and the f-stop) you are going to need a lot of light. A LOT. How much exactly, I can't say... I tried to look it up, but even the American Cinematographer Manual (under the "Incident Tungsten Light Table") doesn't even bother giving footcandle ratings for 200 speed film for anything higher than f8... it would be just so unusual for anyone to try to shoot interiors under tungsten with film that slow with such a high f-stop. (By the way, the ACM for 200ASA at f8 lists the need for 400 footcandles, but that's for a 175 degree shutter. To go to f11, you would need to double that to 800 footcandles... and on top of that to go with a 150 degree shutter you'll need even more, maybe 1000 or so).

I'd say some testing would be in order if you are committed to those other parameters. But definitely 600w tungstens won't cut it...

[reggie ronconi] "...maybe be able to intensify the illumination with barn doors..."

Well, barn doors are never going to intensify illumination... they are only going to flag/cut (i.e. reduce) illumination.

If you have to use that iris/film combo, I would guess that some HMIs are in order if you have to do it that way.

Can you tell us more about your project, and why you have to have that very specific film speed and iris?


T2

__________________________________
Todd Terry
Creative Director
Fantastic Plastic Entertainment, Inc.
fantasticplastic.com






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reggie ronconi
Re: how much wattage?
on Mar 13, 2008 at 3:37:42 am

Hi, Todd,

I'm not attached to the film speed. Grain doesn't matter that much, so yes, I could go to 500T. Actually, I need relatively shallow depth of field, but because of the stops I need to add based on the filtration, I'm cutting down depth of field by opening up the aperture anyway. See, it's that the actual shot needs to be more than 4 stops larger aperture than f11, i.e. ultimately I'm using an f-stop of larger aperture than 2.8 even though there's enough light falling on the subject for an unfiltered measurement of f11.

The project is actually just a test, of sort of extreme color filter use. I'm using the stop values attributed to each filter I've chosen based on the specs provided on the filter manufacturer's website. In other words I need a lot of light because I'm going to be cutting that light back severely. Unless I'm misunderstanding 'stop value=4 2/3", I need a lot of light to use that filter.

The f stop on the camera/lens I have access to won't go wider than f1.9, so this adds up to using a lot of light to be able to shoot this at all.

Thanks for pointing that out about the barn doors, wasn't thinking about the fact that they're absorbing the light they block, not redirecting it. Pretty bonehead I guess.

Does any of this make the situation more clear? I know, everyone who hears about this project thinks I need f11 because I want lots of depth of field, but that's actually not so.

Do you mind letting me know how using 500T might change the situation, since you seem to have an ASC manual nearby? I had actually ruled 500T out as possibly giving me too much depth of field all over again, but....









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Todd Terry
Re: how much wattage?
on Mar 13, 2008 at 4:09:49 am

[reggie ronconi] "Do you mind letting me know how using 500T might change the situation, since you seem to have an ASC manual nearby?"

Don't have to look that one up, that's easy breezy... 500T is going to be about a stop and a half faster than 200T... ergo, 500T will need less than half as much illumination than 200T (considering same frame rate, shutter angle, and iris).

So, if I am understanding you right, you will not actually be shooting at f11, but will in reality shooting with the lens wide open (f1.9)... but due to the filters you are piling on you will be shooting at an effective f11... is that right?

[reggie ronconi] "I had actually ruled 500T out as possibly giving me too much depth of field"

I don't think that's a worry... with that much filtration I think you are still going to have to shoot pretty much wide open, unless you have a couple of 12Ks as lighting instruments (or decide to shoot outdoors in direct sunlight). If you are still worried about the depth of field getting too deep, keep a pack of ND filters handy (.3, .6, .9) so you can open the lens back up... but I'll bet the farm that you won't need them.


T2

__________________________________
Todd Terry
Creative Director
Fantastic Plastic Entertainment, Inc.
fantasticplastic.com






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reggie ronconi
Re: how much wattage?
on Mar 13, 2008 at 5:03:26 am

Hi, Todd, thanks again,

Yes, it's the difference between 'actual' f-stop and 'effective' f-stop that I'm talking about.

I'm checking with the filter manufacturer to be sure they do mean 'stop value' for these filters and not 'filter factor'.... They're listing increments of 1/3 so I doubt I've misunderstood, just kind of wishful thinking that there could be additional reasons to need less light and still use the 200T.

You can probably tell I'm not a cinematographer. (Usually do post-production). Thanks for your patience.








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