LensRentals looks into the Canon EF 16-35 f/4 IS
LensRentals looks inside the Canon 16-35 f/4 IS
This view shows the front element adjustment assembly of the 16-35mm F4. According to Roger:
'The screw collar on the left is not adjustable, but there are adjustable concentrics at the other two locations at that element, allowing some tilt of that element also. There’s still a ramp, so rotation of the front element is used to correct spacing. This is definitely an improvement from the 16-35 f/2.8.'
Click here to see the full Canon EF 16-35 f/4 IS disassembly, and read Roger's detailed commentary.