Nikon 18-70mm and Tokina 11-16mm aperture blades visible even wide open?

I own both lenses, both Nikon F mount obviously. Basically, when mounted onto my D80, all lens' apertures are wide open to allow for a bright and clear viewfinder image, only stopping down to the user's selected f-stop at the moment of exposure.

However, I've noticed that even wide open, both my Nikon 18-70mm f3.5-4.5G and Tokina 11-16mm f2.8 lens aperture blades are clearly visible, forming a polygon shape. In essence, the aperture appears to be partly closed even when it's supposed to be completely wide open.

I've dismounted the lenses and played around with the aperture pin on them, and when pushed to the very end the aperture still appears to be partly closed instead of completely open as it's supposed to. This shows that it's not the camera aperture lever's problems.

The camera still displays the proper fstop (f2.8 for the 11-16 and f4.5 at 70mm for the 18-70) numbers, the aperture blades don't stick or have oil on them, and the images appear to be properly exposed instead of underexposed.

Is this normal? Can owners of the same lenses tell me if they also notice the same thing?

Aperture settings are completely relative to the focal length of the lens. When your Nikon lens is zoomed fully out at 18mm, the aperture at f/3.5 will be 18mm ÷ 3.5 = 5.14mm wide. When zoomed in to 70mm, the widest it will go is 70mm ÷ 4.5 = 15.55mm. (For whatever reason, the aperture can't open to 20mm, which would correspond to f/3.5 at 70mm.) Judging these sizes visually is practically impossible since you are seeing the blades through at least one lens element. (They'll appear much wider looking through the mount end, and possibly smaller when looking through the front end.)

So the only real way to judge if your lenses are working properly is to compare shots taken with different combinations of aperture and shutter speed. If you take shots on Manual mode at f/5.6 1/500 s. And f/22 1/30 s., they should appear equally exposed. You can also use the thumb wheel in Program mode to shift settings while keeping the same exposure (with P* visible on the display) and shooting the same scene.

You can also compare shots against a known working lens (such as at a camera shop). And if the shots do turn out different, leave the lens at the shop for repair.