I am rather puzzled by my Tamron SP AF17-50mm F/2.8 XR Di II LD Aspherical [IF].
Isn't IF means internal focusing, where is does not change the physical length of the lens?
Why is it that when I zoom the lens, it extended the physical length of the lens?
Or does it means that it doesn't change the length when focusing? I blur liao.... any sifu can help enlighten me?