"I discovered that one amateur astronomer had already posted online about how he had detected a known exoplanet using a digital single-lens reflex (DSLR) camera outfitted with a telephoto lens. He was able to discern the dip in the brightness of a star as an orbiting planet passed in front of it - a technique known as transit detection. The exoplanet he chose to go after was a gas giant that belongs to a binary star system variously named HD 189733, HIP 98505, or V452 Vulpeculae, depending on the star catalog."
More: DIY Exoplanet Detector, IEEE Spectrum
Also: Detect known exoplanet with DSLR/telephote lens, Cloudy Nights