rated as

[Geoff Haas]

I have often read about rating a stock at a different ISO (for instance 800 T "rated at" 1600). What are the technical considerations for doing this? How do you set your stop/meter? Also what are the objectives generally? I would imagine this would push the grain, what else? Thanks for any discussion.

[John Pytlak RIP]

The film manufacturer rates each type of film with an Exposure Index (EI):

 

http://www.kodak.com/global/en/service/tib/tib5209.shtml

 

Generally, film exposed at the rated EI and processed normally will give very satisfactory results.

 

A cinematographer may decide to "rate" the film above or below the film manufacturers's suggested EI.

 

For example, to get more shadow detail and "richer" blacks, the cinematographer may decide to rate an EI500 film at EI 320 (give the film 2/3 stop more exposure).

Moderate overexposure of a color negative film will also slightly increase color saturation and have less graininess (because the scene information is placed higher on the film's sensitometric curve, using the finer grained mid and slow emulsions).

 

Or if the light is low, they may decide to accept a slightly grainier image with less detail in the shadows, and rate the EI500 film at EI800 (2/3 stop less exposure). Or decide to use a "Push-1" process, and rate the film at EI1000, knowing that the lower exposure and puch process will increase the graininess and contrast somewhat, and won't have the shadow detail of a "normal" exposure and process.

 

Here is an incident light exposure table:

 

http://www.kodak.com/US/en/motion/support/h2/ilit.shtml

 

And techical information for Kodak color negative films:

 

http://www.kodak.com/US/en/motion/products...0.1.4.4.4&lc=en