Astrodon Exo-Planet filter is used in amateur-scale telescopes to measure light curves of exoplanets.
Although it may not seem possible at first, astronomers with typical backyard equipment and sensitive CCD cameras have the capability to quantitatively measure small changes in light intensity as large exoplanets pass in front of their suns.
Based upon the extensive work of Bruce Gary in his book, “Exoplanet Observing for Amateurs”, Chapter 7 concludes that a “clear with blue-blocking filter should be the amateur’s default choice for exoplanets.”
The Astrodon ExoPlanet-BB filter is that filter, where BB stands for “blue blocking.” He concluded that this filter “has most of the high signal-to-noise advantages associated with unfiltered observing, yet it has most of the reduced systematics advantages associated with V-band and R-band observing.” He recommended this filter for transiting exoplanets, or BTEs (those brighter than 10th magnitude assuming a telescope <16 inches in diameter). The rewards for using the CBB filter are that reference stars that are a different color from the target star won’t produce annoying air mass curvatures in the light curve. Also, most moonlight is blocked by the CBB filter, leading to greater SNR. Finally, observations with the CBB filter exhibit lower atmospheric extinction. For an average star, the CCB filter will have a magnitude penalty of about 0.11 compared to a colorless (clear) filter.