T and f Numbers in Digital Photography

The f numbers express in a strict form, the relation between focal length and the diameter of the aperture. We consider them synonymous to the intensity of transmission because the loss of intensity derived from the pass of light through the lenses worthless. Nonetheless, in complex lenses with a notable number of lenses, the effective transmission of light can be reduced a lot. Therefore, to avoid exposure errors, many manufacturers note the effective transmission capacity ( T numbers) of each aperture along with the f numbers when both values are different.