Stocks making the biggest moves after hours: Cognex, Akamai & more
Check out the companies making headlines after the bell:

Cognex stock plummeted more than 16 percent after hours. The machine vision systems company reported earnings that beat analyst expectations but slightly missed on revenues. Guidance was very weak with 2018 revenue looking to be 10 percent lower than expected.

Akamai shares rose more than 3 percent in the extended session after reporting earnings and revenue that beat Wall Street estimates.

Allison Transmission stock surged more than 3 percent post-market. The transmissions manufacturer beat expectations on top and bottom lines. It also increased its revenue and sales guidance for the upcoming year.

Shares of Tenet Healthcare gained 5 percent in extended trading. The hospital company reported revenues and earnings that surpassed analyst expectations. Its earnings guidance was also raised well above estimates.

Inogen stock soared more than 22 percent after the bell. The med-tech company's earnings and revenue exceeded Wall Street's estimates, partially due to an income tax benefit of $1.1 million in the first quarter. The company also raised its 2018 guidance.

Electronics for Imaging shares jumped almost 5 percent post-market. The printing technology company's earnings fell in line with estimates but its revenue was higher than expected.