Filters are becoming a thing of the past but for a landscape photographer they are one of his best tools. I am a photographer that started in the film era where there was no "Chimping" or "Photoshop" where things can be corrected after the fact. You had to get it as right as you could "In Camera" . Most filters nowadays can be duplicated in some sort of Editing Programs like Photoshop and Lightroom. The problem here is the more that you do in post production the more that the image is damaged. My goal is to get it as good as I can "In Camera" and then take it to Photoshop or Lightroom to do final touch up. I consider this to be the best way to get good photographs.
There are all shapes and sizes of filters. They come in round,square,screw mount and filter holder systems. Filters help the photographer let you see what he sees. When unwanted light like in a sunrise or sunset I used a graduated neutral density filter to tone down the brighter part of the frame so I could pick up some detail in the foreground. With out the filter you get the foreground under exposed and the background over exposed so we use filters to trick the camera. There are all types of filters I mentioned a neutral density filter but there are many others from polarizers , UV filters, Colored Filters. The main filters I use are Neutral density filters that darken all or parts of the photo without changing the color. There are different types of neutral density filters , Plain, Graduated,Soft graduated and hard graduated filters. These filters help you take photo’s when the light is very difficult to get the correct exposure like sunrises and sunsets. They can also bring out detail in flat light. The sunset below was taken with a graduated Neutral Density filter attached to tone down the bright sky and bring out detail in the foreground. Polarizers are the other type of filters I use. Polarizers are like sunglasses for your lens. When you put on a pair of sunglasses notice how the grass,sky and things just pop the same thing happens with this filter. It will take the glair off of water and shiny things. They will also enhance the sky making it bluer that you normally see it. The polarizer is the only filter that cannot be duplicated in post production.
I use two different styles of filters Screw on filters and ones that require filter holders. My main filter system is made by Lee Filters. I use their filter holder and filters . This type of filters can be very expensive but its because they are hand made. Here is a link to a youtube video of the Lee Filter Factory http://www.youtube.com/watch?v=lMu_m203YaY its very cool to see how they are made. Filters can enhance your photos if you give them a chance.