This is not going to be exhaustive by any stretch, but I’ll try to cover the most common filters… 🙂
- UV Filters
The UV filter is probably the most common filter out there. It is a clear filter that doesn’t look like it does anything at all. Actually, UV filters are largely obsolete, they were necessary for film cameras, but I’m pretty sure digital cameras don’t need them to filter out UV rays. Pretty much the only reason people use them nowadays is for protecting the front of their lens. (It’s much easier and cheaper to get a new filter than to fix a scratched or cracked front element in your lens.) There are lots of different kinds of “clear” filters, and photographers have debated endlessly about whether it’s actually better to use a protective filter, or not. (The theory is that cheap filters degrade the quality of your image, so what’s the point in “protecting” your lens from theoretical damage, only to have your image quality suffer as a result?) You will learn about everything you could possible need to know from the Lens Rentals blog, here’s a link to get you started: https://www.lensrentals.com/blog/2017/06/the-comprehensive-ranking-of-the-major-uv-filters-on-the-market/ (Check out the links in the first paragraph of the article for more details.) Also see James’s blog post about a protective filter here: https://www.lenspiration.com/2012/03/should-i-use-a-uv-filter/
- Circular Polarizing Filters (CPL)
A polarizing filter does just what it says, it filters polarized light. 🙂 I don’t pretend to understand all the science behind it, but basically that means that CPLs will reduce haze and cut reflections in your photo. Photographers use them most often when photographing water/waterfalls. I’m sure @JamesStaddon can show some examples with and without a CPL. Wet rocks tend to reflect the sky and water around them, and look sort of ugly. A CPL will usually do a pretty good job of getting rid of that sort of thing. A CPL will also (usually) make blue skies bluer and green grass greener. Generally you just get a much nicer looking image when used properly. (If you’ve ever put on a pair of polarized sunglasses, you’ll know what I mean). One down-side to using a CPL is that it cuts down a lot on the light hitting the sensor, which means you have to compensate with a higher ISO or slower shutter speed, or wider aperture. I think the manufacturers usually say you lose 1-2 stops of light with a CPL. You definitely don’t want to use a CPL indoors unless you have a very special and specific reason for doing so. I’ve heard of using a CPL with a long telephoto lens to cut haze in the distance, but I’ve never tested it, so take it with a grain of salt.
- Neutral Density Filters (ND filters)
An ND filter is sort of like sunglasses for your camera, it makes things darker. Interestingly enough, an ND filter is also commonly used for water/waterfall photography! If you’ve ever seen a photo of water where the water is just a creamy white blur, chance are you’re seeing a CPL or ND at work. While a CPL does cut down on the light a little bit, an ND filter is specifically designed to cut down light, sometimes a lot of light! You can buy different “strengths” of ND filters, some can cut up to 8 stops of light! So any time you’re photographing a scene that has too much light for your camera settings, you pop on an ND filter, and presto! you can now use the settings you want to capture the scene. One example I’ve heard of is when you’re using a fast lens like a 50mm f/1.4 wide open in broad daylight, your camera meter maxes out, and it’s overexposing. You could stop down, but then you lose your nice bokeh in the background. If you have a 3 stop ND filter along, you can just pop it on, and shoot away. Beware that filter “strength” numbers can be very confusing, you’ll probably want to read this article about how different manufacturers measure “strength” differently.
Those are the 3 main types of filters that photographers use. There are other types of filters, (warming & cooling filters, special effect filters, etc) but digital photography and post-processing techniques have rendered them pretty much obsolete.
Feel free to ask if you have any questions, I’ll be happy to answer them! 🙂