I think George has hit the nail on the head. I would be bad marketing for a company to tell the public their film is EI 64 when the competition claims EI 100. So, as George states, they offer a development time that yields correct midtone densities at the inflated EI, thereby sacrificing shadow detail.(posted 8389 days ago)Take almost any nominally rated 100 speed film, cut it's EI to 64, reduce development by 25% from the recommended time, and you will see a marked improvment in overall image quality. And you will have a far easier negative to print, too. But don't expect Kodak, Fuji or Ilford to tell you this. Ask them and they'll tell you their film is indeed ISO 100. Period.