Lenses don't collect dust and grit. They might get the occasiona speck which is easily removed by a puff of breth. I have a biger issue with putting my fingers on them in the course of handling, but big deal - I wipe it off. It's GLASS. A very hard substance. Even mid-50's Russian coatings are tough enough to tolerare a clean cotton t-shirt. How many people have scratches all over their bathroom mirror? I bet very few treat it like a precision instrument 🙂
Filters cause flare and ghosting. End of story. The rarity of such artifacts is directly related to the rarity of a light source in the frame.
I use coated lenses. Seems incomprehensible that one would then add a flare inducer to such a lens. Oh, sure, all your filters are coated, you never take a picture with light sources in the frame, you only shoot pictures on the third saturday in may, etc. etc. why bother carrying a camera?
Too many images ruined by filters for me, thank you very much.
Seriously, UV filters "protection" filters are easy money from suckers. If the cost of the lens was so dear, why waste money on a filter when you can exercise a tiny bit of caution when carrying a camera? They make "lens paper," "lens cloth," and "lens cleaner" for a reason. And I don't know if lens caps are unique to my region, but I've been using one now for quite a while, and find them very handy for keeping my lenses clean when not in use.
I'd use a UV filter at high altitude. That's it. I used an expensive coated one for a bit with color film, and found it had an obvious detrimental effect on the images. Sure, I could still take a good picture with it, but it was easy to see that I had more without it and the negative effects such as flare that came with.
JUst say no to filters except for special effects. Colored filters are great for some shots with B&W film. But for the majority of my shots, I can't see any filter helping. And some B&W films don't need a filter to capture things like clouds in the sky.
It really doesn't matter. You can shoot with them for 50 years, and I'll still say they are unnecessary and you'll still say I can't possibly get by without one.