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#1 Ashley Barron

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Posted 29 June 2008 - 06:26 PM

Hi there,
I've been learning about rating film stocks etc. and I'm slightly confused about the whole process. I know that you can be working with a 500ASA stock but rate it at 100 - that means you compensate with your readings etc. correct? Is that all there is to rating, or is there more involved?
Thank you in advance,
Ashley.
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#2 Jonathan Bowerbank

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Posted 29 June 2008 - 10:30 PM

100 is a bit extreme for a 500 stock (over 2+ stops). You don't want to overexpose too much. Film has a lot of latitude, but you do lose detail if you go a bit too far either way (under/overexposure).

I like to rate 500 at 320ASA so I'm over exposing just 2/3's of a stop. That way a bit more information is recorded onto the negative, it's a denser negative so there's less grain and the color saturation is just right.

It always depends on what you're going for. Some DP's go the other way, rating 500 stock at 1000 (thereby underexposing) then they either correct or push the stock to correct exposure in post to get a specific look.

As you shoot more and more film, you'll come to understand this more and more.
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#3 Andrew Koch

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Posted 30 June 2008 - 12:32 AM

Changing the rating means you are either overexposing or underexposing. If you rate the film higher than film manufacturer's ISO, then you are underexposing it. If you rate the film lower, then you are overexposing it. Halfing or Doubling the ISO equals one full stop. 500 rated at 1000 is a full stop under for example. ISO numbers are in increments of 3rds (Ex. 100, 125, 160, 200, 250, 320, 400, 500, 640, 800, 1000).

Here is one simple way to rate your film. Let's say you have 5218 Vision2 500T (or 7218 for 16mm). Kodak is rating the film at 500, but you want to rate it at 320, effectively overxposing the film by 2/3 of a stop (since 320 is 2 increments away from 500. 1/3 would be 400). Set your lightmeter to 320. Place a greycard under flat even light that you want to be rendered as white light (Ex. If you want tungsten to look "normal" on tungsten film, then light it with tungsten light and don't let any lights of other color temperatures spill on to the card.) Take a meter reading of the greycard. Shoot it at the same stop the meter says. If it says 5.6, shoot it at a 5.6, do not make any compensations. By setting the meter to 320, the meter is automatically giving you the reading that will overexpose the film by 2/3 of a stop. Shoot the rest of the roll with your meter set to 320 and do not make any compensations, let the meter do the math for you. Make a note for the colorist to time to your greyscale. When you go to print or telecine this footage, the colorist will calibrate the printer lights or telecine machine to your greyscale to compensate for your overexposure and bring it back to normal. The result is richer blacks, tighter grain, and greater saturation.
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#4 Jonathan Bruno

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Posted 30 June 2008 - 02:40 AM

As always, Andrew has covered all the important steps. I was just going to add a side note that a big reason that people don't like the 500T - whether it be 18 or 19 - on 16mm is because they rate it at 500ASA. I have heard and seen by experience that 320 ASA is a really good place to start to tighten the grain. If you're shooting on 35mm, on the other hand, the difference is not as crucial. I know that for some of the darker scenes in I Am Legend, they reated at 1000 and didn't push or pull, and the grain still looks damn good.

Basically, take a bunch a film and shoot a bunch of color charts, and similar lighting set ups at different ratings and see what you like. There isn't a right or wrong way to do it, but I would would agree with Jonathan that 2 stops is pushing it, pardon the pun.

Good luck!
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#5 Ashley Barron

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Posted 30 June 2008 - 05:24 AM

Thanks guys, that has really helped!
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