The Lee Frost book is more about filters and film cameras, but has great background on why certain filters are used. The Ross Hoddinnott book is more about digital cameras and filters, but also has some good background on complimentary Photoshop techniques. Together they are a great resource.

• Choosing a filter, click here.
• UV filters tested, click here.
• CP filters tested, click here.
• Using CP filters in the field, here. The 2015 tests here.
• Are Haida Filters as good as B+W? here.
• Singh Ray Blog, click here.
• Tiffen Blog, click here.
• Thom Hogan, click here.
• Cheap verse premium filters. here. Premium brand limited to Hoya.