Do people use filters on their lenses?  Seems there's 2 schools of thought to filter or not to filter.  I'm in the filter camp as it's better to trash a filter than a lens.  Vanity part is what filter do you use?  Recently I've been using Hoya Fusion filters but they look crap and clunky on Leica D-Lux 109 (a rare compact that is threaded for filters along with Panasonic LX100) and the Olympus 45mm F1.8 which has a tiny 37mm diameter filter.  For those I've used the Cokin Pure Harmonie filters which are pretty much invisible and seem to work OK, and they're French & trendy.
The other day after a few Evian's followed by a snifter of Badoit my Olympus with the 17mm lens somehow had an unexplained issue with some furniture and the result was a dented lens cap & filter but the lens was OK.  Sooo I think UV / lens protection filters are a good idea.  Thoughts?

I think that UV filters are a very good idea; however, when I tried to buy one for my Canon Poweshot camera I seem to recall that the filter was quite reasonably priced, but the adaptor I needed to fit it was exorbitantly expensive, so I didn't bother. If I had a camera with an appropriate filter thread, I'd buy one.

A while ago I was teaching a DSLR newbie how to get more out of his camera. At that time I didn't have a DSLR, only a compact (though I used a lot of film at the time).
We struggled to get sharp images on the DSLR, when zoomed in they looked soft even though we were using a tripod and proper focus techniques. My hand held compact looked way better!

After some food in evening I suggested we take a shot of the pub for him to experience low light photography.
They were terrible - flare artefacts everywhere!
A flash of inspiration and I asked him to take the protection filter off.
The results were perfect.

And the punchline....
He put the filter straight back on the camera and as far as I know never took it off 
There are people who 'need' filters and those that don't.

My 2p - the negatives
Good quality filters are a lot better than the one I described, but even the best filter will still degrade the image slightly.
Cave photography has exceptionally high contrast, some lenses like the Canon 24-105 f4 L flare even without a filter. Adding a filter on this lens would be a bad idea.
Tests I have read show filters are far less strong than the lenses they are protecting. When filters break they can scratch the lens. Most filters actually make damaging the lens more likely.

My 2p - the positives
Filters are highly recommended in a sandy environment to prevent scratching when cleaning - a good idea in dry dusty continental caves.
Some lenses need a filter to complete their environmental sealing - a good idea in UK caves.
Use your lens hood - they protect the lens far better than a filter, and if you are using a filter then they still add another layer of protection.

I don't use them and just be careful/use the lens cap. I can see they would be useful for some people but I only very rarely use that camera when the lens can be scratched and I need to use the camera at the same time as I have a tough camera for those situations (I don't take my Olympus micro 4/3 underground).

On the vanity side of it if I was to use them I would just but the cheapest filter available as I personally wouldn't be fussed how it looks.

There's two problems filters can introduce, reduced image quality and flare.

As for reduced imaged quality:
I always used a cheap ebay UV filter for caving photos. I tested it above ground and could not see any difference between with the filter on or off at 100% magnification. However, I used multiple flashes so I was often at f8 or smaller. Down at f2.8 or lower, aberrations may be more apparent. I also used an 8mp camera, but really, unless you're printing big or selling images, if an aberration is not visible at 8mp, its not that important.

Underground, the main way I found to lose image quality was to have water droplets, fine condensation, or grease/mud on the lens or filter. These are all refracting materials and will ruin an image if present in more than tiny amounts. A cheap uncoated filter allowed me to clean these off without worrying about damaging anything important. Dust isn't a problem as it absorbs instead of transmits, so simply darkens the image a little. Small scratches are less of a problem for larger sensor cameras as they're not resolved and so just reduced the contrast a little, which is easily correctable in post.

As for flare:
I never saw ghosts or significant flare. I used a prime, which helps, and never pointed a flash directly at the camera unless something was in the way. I find above ground to be much worse for UV filters as there many more direct point sources of light (such as the sun, or lights in a pub). If you're still concerned about this, these tests may be useful:
https://www.lensrentals.com/blog/2017/06/the-comprehensive-ranking-of-the-major-uv-filters-on-the-market/

I certainly agree with Duncan S on the lens hood; they're not so fashionable any more but have many of the upsides of filters with none of the downsides. With wide lenses though, they have to be shorter and so are less effective. Also, bring something to dry and clean the lens as wiping off condensation with a damp polyester undersuit is not effective.

I keep filters on all my lenses as I'm often shooting in muddy, wet horrid places and often need to wipe the lens. I started out using expensive hoya filters but have now gone the opposite way and purchase really cheap filters from China as I can get 40 of these for the same price as a top Hoya filter and treat them as disposable items, often changing them after only one weekend.

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ZombieCake said:

The other day after a few Evian's followed by a snifter of Badoit

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It's all been said above, just remember that you can take them off and put them back on again

Fulk said:

I think that UV filters are a very good idea; however, when I tried to buy one for my Canon Poweshot camera I seem to recall that the filter was quite reasonably priced, but the adaptor I needed to fit it was exorbitantly expensive, so I didn't bother. If I had a camera with an appropriate filter thread, I'd buy one.

Click to expand...

I don't know which adaptor you need but there are many on Ebay. I have a 40.5mm to 52mm Zomei which cost a couple of quid and is a good quality metal adaptor.

If you look down the listings on Amazon it's sometimes possible to pick up high quality old stock filters by e.g. Tiffen at very low prices. Many filters, particularly coloured filters, were made for the film era and are often ignored by digital photographers, hence the low prices. The filter colour, provided it is not extreme, is corrected by your camera's white balance or in post processing. I use a Hoya B2a (blue) with no problems.