Originally posted by GUB Wasn't the importance of Tstops in the film industry mostly to do with cutting from one lens in a scene to another without an ability to edit the subtle change in exposure? Not really relevant here in the still world especially considering the difference between Tstop and fstop maxed out at under 1/3 of a stop. And the difference between two lenses would likely be considerably less than that.
Most films I worked on back in the film era, the Director of Photography (aka cinematographer) would predetermine what ISO and what T-stop the entire film would be shot at to create a consistent aesthetic. There were preset EVs established; not variable. Fast apertures were common to enhance and isolate the protagonist but regardless of the T-stop chosen, lights, scrims, filters, gels, flags, and silks, all manners of controlling the EV to match the T-stop.
I should also mention that much of the control was also for desired and consistent contrast ratios between the key and fill lights in a controlled zone system. Shooting in the studio, thus, was much easier than on location.
Even when the cinematographer and his gaffer nailed consistent light and contrast ratios, and even when the film was processed by the best of labs, the negative still had to be analyzed and corrected by a printer that produced an internegative. This meant density (exposure) and color balance adjustments. The same happens digitally with whatever editing software is being using such as AVID.
When you're spending a million dollars a day shooting a film, 1/3 EV is visible between shots, and even when the printer can adjust for that, there is a shift in contrast and color balance as well. Careers have flourished or failed because of these nuances and many British, Czech and Italian cinematographers found favor because of their incredible attention to detail on both the technical precision, but also how that translated to style. Of course there are many great American cinematographers, but there is a disproportionate non-native US representation of cinematographers in Hollywood.
Although not all "cine" lenses have T-stops, the lion's share are made by Zeiss, Arri, and Rokinon. Whitepoint is the only pro level cine lens that uses f/stops.
I understand the argument that Tstops are 'not really relevant' in still photography, but I know lens makers know the transmission values of their lenses at various apertures, so why not give us the True stop and not a theoretical focal length/diameter of the aperture?
One example: The Canon EF 35mm f/1.4L II USM has tested at T1.8, 1/2 EV less than the f/stop would seem to claim. Assuming Canon's math is correct, the reality is different because of the lens design and coatings. I would want to know that before spending nearly $2k for an f/1.4 that was really giving me f/1.8. On the other hand, the Canon EF 35mm f/2 IS USM at less than half the price is T2 and thus the f/stop and T-stops are the same.
If I were a Canon shooter, I would prefer to not have to research if my f/1.4 was really more like an f/1.8 or that my f/2 is actually an f/2. With T-stops there is science and reality and with f/stops it's a less reliable value. You know we often say "it is what it is" but the truth is often "it is what it is sort of and sometimes".