[vize]

I recently acquired a Quantaray 28-70mm f/2.8-4 K-mount manual focus lens with 'A' setting.
When I keep the aperture in the A-setting and in Av mode (pentax k-x), the aperture stays at f/2.8 as I zoom from 28mm to 70mm.

How is this possible, according to the lens specs it is f/2.8-4, so the maximum aperture at 70mm should be f/4 correct?

Anybody has seen this before or can shed some light on this?

Thanks.