Will using a lens filter make my photos less sharp?
Whether a lens filter causes a loss of sharpness really depends on the quality of the filter and the type of material from which it’s made. The highest quality filters are made from optically pure glass, and they range from moderately to extremely expensive (the best cost hundreds of dollars). Several manufacturers make high-quality resin filters that are less expensive and very close to glass in their optical purity. There are also inexpensive plastic filters on the market, although, it’s not a good idea to use a cheap filter on an expensive lens.
High-quality optical filters of glass or resin won’t reduce sharpness or image contrast — provided that you use only one filter at a time and that you keep them clean. That being said, any time that you add additional glass elements to a lens you increase the likelihood of things like flare and internal surface reflections (reflections between the front element of the lens and the rear filter surface) that are sometimes called ghosting. These problems are compounded if you stack more than one filter on at a time — such as putting a polarizing filter over a protective ultraviolet (UV) filter. Stacking introduces multiple surfaces onto which internal reflections can propagate.
How does the lens aperture that I’m using affect lens sharpness?
New photographers are often surprised ...