Originally posted by UncleVanya But if a simpler design at f/1.8 gathers the same or more light as a very complex f1.4 design the resulting exposure could favor the f/1.8 lens in low light over the f/1.4 - this is the question the OP is asking
As you say it could.... but what are the odds?
My guess is, next to zero. Modern sensors have at least a half stop latitude when determining correct exposures. First, for that to be true, you'd have to establish that in your ideal test circumstances where theoretically it could make a difference, there would be a discernible difference in photo quality. Until that is done, it's just speculation. It' pretty pointless discussion the theoretical importance of various lens attributes when no real world differences have been reported. Common practice says it's irrelevant. I'm going with that until shown a circumstance where it isn't. Then we'll have something we can analyze.
First establish that something happens. Then determine how often it happens. Then you have a result you can trumpet form the roof tops. Often, the theoretical difference makes no practical difference. I also don't accept the idea that an extra chocolate chip will in any meaningful way affect the taste of my chocolate chip cookies.
Back when I was a department head, part of my responsibility as i saw it was telling new teachers which parts of the education act they could safely ignore. If you followed everything down to the letter, that was a sure recipe for a mental meltdown. Sometimes, knowing what to ignore is as important as knowing what to do.
What are T-values for you ask? IN the motion picture industry, it is necessary to maintain exact exposure values for different pieces of film that may be spliced together at some point. Exact values are needed because of the need to create the illusion of continuity. And most movie cameras are not TTL metering. T values are of interest to filmmakers and perhaps photographers using hand held light meters. They do have a purpose, but for the most part, it's not still DSLR photography.