How does the F value of ordinary lens compare with the T value of focal plane? For example, which aperture is larger, normal 1.4 or movie head t 1.5?

The light transmittance is measured according to the illumination of the image plane. It corrects the F value according to the influence of lens structure, lens material and lens coating on the light transmittance, which is more scientific and accurate than the F value. Although the aperture value of different lenses is the same, the light transmittance is not necessarily the same, and sometimes there are obvious differences, which is one of the reasons why some old lenses must be exposed and compensated on digital computers. Due to the development of lens coating technology, the difference between T value and F value is very small at present, and the general F value can meet the needs. Only focus plane with stricter exposure requirements can use the t value.

Back to your question, for the lens with the same value of T and F, the actual luminous flux of the lens marked with T must be greater than that marked with F; However, as for the lens with different but similar values of F and T, it is not known which has the greater luminous flux.