I'm practicing with Sigma 28 - 300mm f/3.5 - 6.3 Macro lens. And the thing I've noticed is that at 300mm focal length my aperture can be set to as wide as f/5.6. And EXIF data confirms it:
I'm wondering how is that technically possible and if the behavior is considered normal?
This is probably because some cameras disable autofocus at slow apertures. The camera manufacturers think that performance won't be good enough, and so they disable it. The third-party lens is reporting inaccurate information to the camera so that it will work anyway — slow and sometimes incorrect, perhaps, but at least the camera will try.
Exposure might be off by a tiny bit as a result, but the third-stop difference between f/5.6 and f/6.3 basically comes out in the wash anyway.
