Tiffen UV filter. I put the filter on without thinking much of to it, until recently (when trying to take pictures of my new rug ... yes rug #6), when I noticed that the filter gives a weird glare. See right next to the pillow, there is this ghosting, kind of looks like a green light? When I removed the filter the glare was gone. I tried out my 50 mm which has a nicer Hoya filter, and there was no glare. I haven't really been happy with my 35mm, and primary have been using my 50, but maybe I will give it another try, sans filter.