What's the difference between the T aperture and the F aperture of a lens?

The t value is the number of exposure stages.

The f value is the aperture series.

To put it simply, the other settings of the camera are the same, and the video shot by two lenses with the same f value (for example, 35mmf 1.8 and 135mmf 1.8) still has light and dark differences.

This is because there will be losses (reflection, refraction and absorption) when light enters the lens.

The t values of the above two lenses may be T2.0 and T2.4 respectively, so the picture taken by 135mm lens will be darker.

However, in film shooting, the brightness requirements of different positions in the same scene are very strict, so a more rigorous t value will be marked.