Originally Posted by Film-Niko
Film-Niko: Well sorry but your methodology must be poor, because that is simply incorrect. Portra 400 has better resolving power than Provia 400X. The MTF curve has a better response. Portra 400 also has whole orders of magnitude more dynamic range. Provia 400X will clip both highlights and shadows at the same time before pushing, pushing it to 1600.. it's just absolutely nasty in that respect.
Also have a look at the characteristic curves, look where the Provia 400X "shoulders" (or toe I guess) the highlights before completely flattening out (not to mention clipping the highlights let alone being flat).
Portra 400 remains a steep straight line for 6 stops past this point where Provia 400X begins to flatten out, with no sign of flattening out into a shoulder yet. Not to mention the highlights aren't going to be clipped.