Quote Originally Posted by StoneNYC View Post
My question, how many films are exactly the exposure level listed on the box?
All of them, yes every last one; that is with one caveat, that it is within the tolerance range of rounding to the closest "normal" ISO number. If a film measures 113 ISO it will be called 125 ISO, if 112 it will be called 100. So to within 1/6th of a stop, yes.

Every deviation we make from the ISO rating and the ISO processing standard to any other speed or process standard is a person specific speed known as an Exposure Index, an EI.

Everything from our metering methods to the accuracy of our thermometers to our choice of paper can affect our personal EI choices.

I'm going to hazard a guess that outside of those who actually do ISO testing for film manufacturers, few if any of us mimic the ISO standards in practice. The film speeds that people brag about "finding" are in fact EI's.

This doesn't mean these films don't or won't do a good job at an EI of 3200 or 400. Box ratings are just numbers.

Even Ilford and Kodak show us various EI's that are workable. This data sheet for Delta 400 is a great example, http://ilfordphoto.com/Webfiles/2010628953322222.pdf see page 3, the numbers in bold.

If Ilford had chosen Microphen as the ISO stand developer for Delta 400 the ISO rating may have been 500, if Perceptol maybe ISO 250.

Quote Originally Posted by StoneNYC View Post
Also, why can't they just make a film speed that is actually 3200? Are there/were there any? Is P3200 really 3200? Which is better for resolution?
In order;
They could, it would have a short shelf life.
None that I know of.
No. 800-1000, depends on developer, see Kodak tech pub.
Don't know.