It probably worked when he added the filter because it moved it further from the lens so that it did focus as it should on the front of his lens. Best to buy from somewhere like jessops where you can try it unless it is the sony one that is guaranteed to work.

And every one said, 'If we only live,
We too will go to sea in a Sieve,---
To the hills of the Chankly Bore!'
Far and few, far and few, Are the lands where the Jumblies live;
Their heads are green, and their hands are blue, And they went to sea in a Sieve.

Edward Lear
http://www.nonsenselit.org/Lear/ns/jumblies.html