That sounds right. When I first shot Ektar I had the issue with the shadows shifting purple or blue and excessive grain showing in those shadows, I thought it looked underexposed. When I read the spec sheet exposure recommendations I just started shooting it at ISO 64 or sometimes 50 and that seemed to cure my Ektar issues. It's interesting because the Portra 400 exposure recommendations for unmetered is two stops higher than Ektar or Portra 160 which is on the overexposure side by a stop vs metered. That supports your theory perfectly and it makes sense.

Quote Originally Posted by MattKing View Post
Now I see where you are coming from.

FWIW, Kodak's "Sunny 16" recommendations for Portra 160 are exactly the same, whereas their recommendations for Ektachrome E100G and E100GX are for one stop less exposure.

Their recommendations for metered exposures are to use the ISO speeds instead.

This tells me that the the "Sunny 16" recommendations are weighted to protect shadow details for negative films, and highlight details for transparency film.

Which makes a certain amount of sense, if you assume that correctly metered exposures are likely to be more accurate than "Sunny 16" exposures.