Ektar is the yang to Portra's yin. It "features high saturation and ultra-vivid color" and "unparalleled fine grain."
It's the descendant of Ektar 25, which was a technical exercise to see just how sharp a film Kodak could make. At the time you knew it was something special because EK brought the august old brand name "Ektar" out of mothballs for it.
Eventually, as film technology continued to improve, Kodak didn't see any disadvantage any more in a version that was four times faster.
Wonder how many "megapixels"-equivalent of information there are in an 8x10 sheet of Ektar 100? Or whether there's any meaningful way to approximate such a thing? That's Ctein's bailiwick. I'll just settle for saying, "bet it's a lot."
Featured Comment by Ctein: "The film's resolution is substantially irrelevant in this case. As Patrick (in the comments) suspected, your 8x10 view camera lens isn't going to be delivering anywhere near that resolution, under any kind of normal working circumstances. If nothing else, consider that ƒ/16 is considered a large aperture for 8 x 10 work. Diffraction effects, focusing errors, and film plane uncertainty will combine to degrade resolution several fold below the theoretical limit of that film.
"That said, ballpark pixel equivalent for 8x10 on really fine-grained, high-resolution film? 150–200 megapixels.
"No, I'm not going to justify that number: a handful of back-of-envelope calculations, informed by a whole bunch of factors, mechanical, optical and psychophysical. Still, I have some faith in it, because it's consistent with comparison tests that Andrew Rodney ran back in the '90s with scanning backs on view cameras. Get up into the 150 megapixel range, and you can generally blow away any view camera.
"No idea about the relative RMS values. RMS is not an accurate indicator of visual graininess for extremely fine-grained films, which is one of the reasons Kodak and other film manufacturers moved away from using it back in the '90s. It also suffers severe quantization errors when the graininess gets really fine; one film might have a reported value of 3 and another a value of 4, and those could correspond to measured noise levels of 3.45 versus 3.55."
Featured Comment by David A. Goldfarb: "Ektar 100 has very fine grain. They currently specify it in terms of Print Grain Index, and I think they were still using RMS granularity when Ektar 25 was being made, so there probably isn't a convenient way to compare, but Ektar 100 uses the same 2-electron sensitization used in Kodak Vision-2 cine films, making it possible to cut grain in half compared to an otherwise similar emulsion of the same speed.
"Here's a test of Ektar 25 vs. 100 and discussion thereof posted on APUG when Ektar 100 first came out."