I recently bought a bunch (5) of lenses for my Nikon Zfc.
Back in the day, when most everybody was shooting black-and-white mostly, and only a little color, it was common practice to mount a skylight filter on the front of a lens, to keep dust and moisture from getting on the front element or into the works. The purpose of a skylight filter was to darken skies in black-and-white photography. So, a skylight filter would do double-duty. If you wanted to use an additional filter, you’d attach it on top of the skylight and take it off when you were done with it, but leaving the skylight attached at all times to protect the lens.
Nowadays, it seems, a neutral density UV filter serves pretty much the same purposes. Scattered UV is one cause of glare and haze. And the filter serves, as always, a layer of protection for the front element’s glass and coating.
One of the lenses I bought has a 46mm filter thread, which appears to be a bit unusual. In searching for one, I discovered that a major brand from way back when — Tiffen — not only is still around, but sold inexpensively. The UV protectors run about seven bucks and change. And the beauty part: they’re made in the USA. (USA! USA! USA!)
Which leads me to the point of this post. If you’re in the market for filters for any purpose, I can recommend to you the Tiffen brand.