Here is just one more consideration. The rotation of the front element when focusing. Cheaper lenses will do this. Normally this isn't an issue unless you are using a creative filter system like Cokin. As they attach to the front element. You will need to keep a weather eye on the filter glass/insert and if you are using a graduated filter you might have to adjust the orientation to ensure correct alignment. Nothing worse than a 45 degree graduated angle effect on the filter to the 180 degree (Flat) horizon.
. The same applies to circular grad and polerising filters on these types of lenses.