Could a filter damage the curved front element of the Canon EF 100mm f/2.8 Macro USM?

Question

I just got the Canon EF 100mm f/2.8 Macro USM and I really want to put a UV filter on the lens to protect the front element, but I feel uneasy screwing one on because of the curved front element. I feel that if I screw in the filter all the way, the front element will rub against the filter and will scratch or at the very least put unecessary pressure on the glass.

The filter I have is Tiffen 58mm that I used previously with my kit lens.

I tried to put a small piece of tissue in the center of the filter and then screwed it on and it seems that the tissue is getting depressed :S I really want to love this lens, but why couldnt they just make the filter thread sticking out further?

Has anyone else experienced issues with filters for this lens?

What about ultra thin filters? Would that help anyway or do they have the same thread depth? Never used one before.

Answer

There might be a chance where certain lens-filter combination can result in the filter touching the surface of the lens. Even if they do not actually make contact, the gap can get to be so small that some dust particle could get squeezed in between and cause damage.

I suggest the following to find if the filter gets too close to the lens: Put your filter on a table, lens side up and pour a drop of lens cleaning fluid in the center. Then screw the lens into the filter without taking it off the table (both must be completely dust free to avoid any damage). Unscrew the lens and observe if the lens is wet. If it is, the filter is too close. Wipe the lens an then the filter with lens cleaning tissue or a quality microfiber cloth.

If you get to prove that the filter touches the lens (or simply want to make sure you wont get any damage from it), you can get the ring out of a somewhat cheap filter and remove the glass, and use that ring between your lens and the filter. Just watch out for vignettes!

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