Choosing a Color/Planetary Filter
There are many different types of optical filters available today - some are used in photography or video, and others are made specifically for visual use. But in each case, the filter is designed for one purpose: to block certain frequencies of light, while allowing other frequencies to pass. The filter's ability to pass only certain frequencies can greatly enhance the observer's ability to discern small details on some solar system and deep sky objects. Special Light Pollution Reduction (LPR), Broadband, and Narrowband filters are designed for observing DSOs. For observing the Moon, Mercury, Venus, Mars, Jupiter, and Saturn, colored filters are the most useful.
The first colored photographic filters were invented by Fredrick Wratten (1840-1926), and the color numbering system he developed is named after him - Wratten Numbers. Wratten sold his company