I have a 72mm (filter size) 15-85 Canon lens. All my others (well actually one other zoom) has a filter size of 77mm as had my previous lenses. No problem, step ring 72 to 77.
I have the lens hood, which cannot now be removed without removing the step ring and UV filter.
So, now I want to use my polarising filter (77mm) - into UV filter. With hood attached this is a wee bit tricky to insert, and even more tricky to remove.
Not a disaster by any means, but b***y annoying in the field.
Someone will have a simple solutiong to this I'm sure ...

