I get this question all the time - “What filters do you use?” I don’t use many filters today, the primary ones are a glass protection filter and the occasional polarizing filter. I do use two different neutral density filters for my long exposures.
So lets get the controversial filter out of the way. I use a clear glass filter to protect the front of my lens. I don’t use a cheap one, I actually use one made by my camera company Nikon. It is not a cheap piece of glass, it is high quality and used to protect the front element from damage. I found that when I am hiking and moving around rocks and other objects that the front of the lens gets dinged, the filter will protect that element from scratches and if I happen to hit the lens real hard the filter will take the punishment and may crack or smash, but usually it will protect the front element. It is far cheaper to replace a damaged filter than the front element. I have never seen it degrade my image because I have this filter on and I feel better that the protection is there. I also find that with constant cleaning of the filter, after a while it does get scratched, that is when I will also replace the filter, again cheaper than repairing the front element. The one caution I will say is to not buy a cheap one, use the highest quality you can afford, I sure find that they are worth it.
The next filter that I use is a polarizer. It basically works like sun glasses, it gets rid of the glare from the sun. It will make the colors deeper as long as there is sun out, if it is completely overcast it really does not work. You need to turn the filter to adjust it, you can see the difference in the viewfinder or just watch your light meter, as you reach full polarization the exposure will drop to a low point, that is usually where I will leave it set, but watch how it looks in the viewfinder or on your monitor, you can back it off if you need to. It will usually bring out deeper colors, making the sky bluer (sometimes too much) and the grass greener, plus you can see into the water, getting rid of reflections. It is a very handy filter to have.
I have only two other filters and they are neutral density filters. They are used to slow down your exposure times. I currently use the Big Stopper (cuts 10 stops of light) and the Little Stopper (cuts 6 stops of light). I use the Little Stopper for water falls, where I need to cut the exposure down to a few seconds, you can still see through this one so it is easier to use than the Big Stopper. I use the Big Stopper for my 1 minute exposures of water, it is good for the times you want very long exposures. I really like the looks of long exposures, it will smooth out water and make clouds smooth and silky.
Those are the only filters I use, I have tried graduated filters, but I can control those more doing the same effect in Lightroom or Photoshop. I will say the two important filters would be the polarizer and the clear filter. Just make sure you buy good quality filters and not the cheap ones that are available, remember these are going in front of your high quality lens, you don’t want to drop that quality by using cheap filters. I am a big fan of B & W, Hoya,Tiffen, or your own camera brand. For specialty filters, I do like Lee, Singray and Cokin. Do your research, there is plenty of info online for filters, so have fun and experiment, that is what makes photography fun.