Yes, I'm an idiot. Dispensed with the aperture LEVER is what I wanted to say. The 300/4 PF having it is a bit of a nasty surprise for those looking to adapt, since it's going to be a popular lens. Ok, back to the OP: The difference between EF and F is about a few mm, so the adapter must be absolutely precise. At 18mm a small error will produce issues. Normally when it comes to adapting I prefer to go with longer glass just to be safe, and use native for shorter lengths.