Thereby, it is also deemed to improve the "bokeh" of the lens, that is the character of the image in the out-of-focus areas.

The f-number in this lens refers to the effective aperture opening and determines the depth-of-field produced by its use.

The T-number refers to the amount of light, which passes through the lens and is collected on the film or sensor, as such, transmission stops are used by the camera to calculate exposure.

Both values differ significantly, because the tinted glass element remains in the optical path all the time.

The optical effect can be emulated by combining depth-of-field bracketing with multi exposure, as implemented in the Minolta Maxxum 7's STF function.