Although we don't believe in timing the market or panicking over market movements, we do like to keep an eye on big changes -- just in case they're material to our investing thesis.

What: Shares of image sensor maker OmniVision Technologies (Nasdaq: OVTI) sank 14% Monday after slashing second-quarter revenue guidance.

So what: Today's warning comes on the heels of a report last month by Chipworks that indicated that Apple's (Nasdaq: AAPL) iPhone 4S uses an image sensor from Sony (NYSE: SNE) instead of OmniVision. While OmniVision's sensors probably won't get entirely cut out of Apple's future iterations, the drop in demand from other customers is now becoming a growing concern to investors.

Now what: OmniVision now sees second-quarter revenue of $212 million to $217 million, which is down from its prior view of $255 million to $275 million and way below the Wall Street consensus of $260.4 million. Management is obviously disappointed with the demand drop, but given that it also announced a $100 million repurchase program, the stock price might actually be a steal. "We believe our stock represents an attractive investment for OmniVision and its investors and that [the buyback] attests to our strong confidence in the long-term strength and viability of the company, its technology and its broad market and product portfolios," CEO Shaw Hong said.

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