Some lenses, particularly adapted motion picture lenses, such as Speed Panchros or Kinoptik, show both the (for us) usual f-Value, as the T-Value. For instance, my 25mm Kinoptik shows an f/value of 2.0 and a T/value of 2.5. On the diaphragm setting ring, only the T-values are indicated. Same for a 18mm Cooke Speed Panchro f/2.0 and T/2.2
Kinoptik 25mm /f=2 /T=2.5
If I understood it correctly, the T-value takes into account the actual light transmitted by the lens, not the theoretical (geometrical) relation between diameter and focal length of a lens.
I would assume that the DOF is computed using the f-value, not the T-value. Correct?
Another question: when we invest for instance in an expensive Leica f/1.4 lens, we do not know how much light really reaches the sensor. Two lenses with the same f/ value may have very different effective luminosity. Correct? In lens tests I read in publications, I have never seen this subject is usually tackled.
Thanks in advance for any answers on this subject and practical consequences when buying / using lenses on the G1 or other cameras.