Thanks for the info. To what on the lens does the "cover on" hood fit to stay in place? Is it simply a friction fit over the lens?I assume that the reference to the thread inside the hood is in fact a thread for a 70mm filter hence the 70mm in the hood's title?

However if the hood simply slides on the cover then presumably a 67mm filter could be used screwed in to the lens thread itself prior to fitting the hood? The drawback with this would be the necessity to pull off the hood everytime you wanted to change filters whereas with the 70mm thread internal to the hood you can change the filter without removal of the hood?

Have I got this correct? Thanks