[JJ_SO]

I use filters only if I need them - polarizer or ND filter. "Protection"-filters in my eyes are useles. The only protection of them is for the filter thread of the lens which would get damaged if the lens falls on a hard floor. And for that I can use a filter ring without glass in it. But if something hits the lens on it's frontside directly, the filter gets damaged and scratch the front lens probably, too.

 

I don't use protection filters on my eye-glasses and those are in heavier use than my lenses usually are.

 

The slimline filters are made for wide-angle lenses with less than 30mm focal length to avoid vignetting. It's hard to tell in general if those are not touching the front lens, but since these versions are a bit more expensive, I suppose they are better designed. It's easy to measure with a caliper: If the distance from the backside of the filter ring to the filter's glass surface is shorter than the length of the thread, it could touch the front lens - but doesn't have to.

 

The danger of getting the front lens getting scratched by a badly designed filter is real. Roger Cigalla once posted some occasions, but I couldn't find the article

 

*Edit: Thank you, dave 9t5, that was the one I was looking for.*

 

Instead I measured some of my filters. The expensive 77mm all would not scratch the front lens, if if isn't higher than the filter thread. The older, cheaper Hoya and Vivitar color filters could do some harm, if the front lens is going very far and coming close to the red dot line

 



But I didn't find a lens which was so close to the red dot line.