What does this statement mean? (Tamron 180mm macro)

[dRebelXT]

Found when research this lens.
http://www.nikonians.org/html/resources/non-nikon_articles/tamron/180-f35/180-3.html

It may be important to mention that this lens transmits -and the camera shows- the effective aperture while at the highest magnification, which is not the case with all macro lenses. .

 

[tltan]

not all lens show effective aperture.

For Tamron 90mm which I have, although you have set it to f2.8, at minimum focusing distance, the camera reflects f5.6 which is the effective.

think thats what it means. Read that some lens actually shows whatever you set although its not performing at that aperture.