Prepare boiling water canner. Heat jars and lids in simmering water until ready for use. Do not boil. Set bands aside.
Prepare pears by peeling, halving and coring them (I use a melon baller). To prevent browning, use a commercial produce protector or submerge pears in a mixture of 1/4 cup lemon juice and 4 cups cold water and drain.
To prepare syrup, combine 2 1/4 cups granulated sugar and 5 1/4 cups water for light syrup OR 3 1/4 cups granulated sugar and 5 cups water for medium syrup in a stainless steel saucepan. Bring to a boil over medium-high heat, stirring until sugar is dissolved. Add split vanilla bean. Reduce heat to low and keep warm until needed, taking care not to boil the syrup down.
Place pears in a single layer (you may have to do two batches) in syrup. Cook over medium low heat for 5 minutes until fruit is heated through.
Take out the vanilla bean and cut it into 4 equal pieces and place one in each jar. Pack hot pears, using a slotted spoon, cavity side down and overlapping layers, into hot jars to within a 1/2-inch of top of jar. Ladle hot syrup into hot jar to cover pears, leaving 1/2-inch headspace. Remove air bubbles and adjust headspace, if necessary, by adding hot syrup. Wipe rim. Center lid on jar. Apply band until fit is fingertip tight.
Process pint jars in a boiling water canner for 20 minutes for pints or 25 minutes for quarts, adjusting for altitude. Remove jars and cool. Check lids for seal after 24 hours. Lid should not flex up and down when center is pressed.