Accuracy of Film Speed Rating - Portra and Fuji

I've looked under some different permutations and haven't seen any answers yet.

How accurate are the rated film speeds for the Portra (NC and VC 160 and 400) and Fuji 160C?

I ask because I want to try my hand at color flash photography and need to make sure my meter is telling me the right exposure.

In b/w I could do a film speed test and figure this out for myself, but I'll be having my lab soup the C41 for me.

Thanks!

The film speeds are rated very accurately by stringent international standards governed by the ISO. The real question is: will your equipment, with all its biases, reflect the film's nature?

For what it's worth, I've found that the Portra films are always looking great when shot at box speed. They have so much latitude (almost 2 stops underexposure and many stops of overexposure) that you could just shoot blindly and it would work anyway.

If your lab can produce real contact sheets, you might nail down a more precise EI with their help.

mhv said:

For what it's worth, I've found that the Portra films are always looking great when shot at box speed.

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I find this as well. I've used 160 Portra VC, 400 Portra NC, and Fuji 160S. My EI for each is the ISO speed. All processed by my local pro lab. Still doing two runs a day of C-41!

I read some where a long time ago that Kodak said the speed of color negative film is 1/3 stop. Professional color slide film is 1/5 stop.

mhv said:

I've found that the Portra films are always looking great when shot at box speed. They have so much latitude that you could just shoot blindly and it would work anyway.

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I agree--well, maybe I wouldn't shoot blindly with it, but it does have a very good amount of latitude. This, combined with the increased color saturation and contrast, makes Portra more of a viable alternative to slide film (in certain situations) than it was in the past.