When it blow in to clear filters, you may well think 'what's the point?' as they don't obviously make a difference to your photo. But, they can be precious in protecting your lens as well as making the front of the lens water, oil and grime resistant. All this while also improving the clarity of your doppelgaengers by cutting out haze.
There are three main types of clear filter:
Protection filters filtering or filters may refer to are designed to be completely fine, with no UV or IR light blocking properties. The filter protects the front element of the lens from scratches, dirt, water and other tramontane matter, and can also make it easier to keep your lens clean, as you can simply remove the filter and clean that as a substitute for of the lens. The Hoya HD Protector is made with toughened glass for additional protection.
UV, or ultraviolet filters, absorb ultraviolet rays that you can't physically see, but can perceive b complete landscape photos hazy and indistinct. Hoya's High Density filter is made from sharp cut UV glass which is chemically elevated and 4x stronger than usual glass. It also has a 8 layer anti-reflective multi-coating which is water and oil repellent, scratch and stain resistant. This lens discretion also serve as a permanent lens protector.
Cokin's pure Harmonie Anti-UV Multi-Coated (UV MC) filter is only 3mm in thickness and is currently the thinnest separate in the world, making it almost invisible when attached to your lens. It has Everclear 5 coating technology, making the filter water repellent, anti-oil, anti-dust anti dirt and scratch resistant.
In the same way as the UV filter, the IR filter blocks infra-red rays. The filter is especially useful if your camera does not from a built-in IR filter on the sensor. Hoya produce a joint UV and IR cut filter that eliminates both at the same time from your images.