The former Hillsdale art teacher who took inappropriate videos of underage girls on his phone will spend 18 months in prison. 29 year-old Robert Altenburger was sentenced Tuesday in Ashland County Municipal Court on five counts of voyeurism. Altetneburger pleaded guilty in December to recording the students, who were between the ages of 11-15. Altenburger will also have to pay a $2,500 fine and register as a sex offender for 15 years once released.