HOYA estimates that the business transfer will be finished by October 1, 2011.
Hoya bought Pentax in 2007 mainly to gain access to its medical technology. Pentax is the world's tenth largest digital camera brand by shipments, with just 1.5 percent of the market, according to research firm IDC.
Ricoh's main business is related to copiers and printers, although the company has also a digital camera business, but sales are too small to feature in global data. The acquisition is expected to allow the company get into the digital single-lens reflex camera market.
The acquisition does not include the digital camera module, DVD pickup lens, endoscope, artificial bone, and voice synthesis businesses of Pentax. They will be retained by Hoya, the companies said.