Lightest, not smallest, 1/2" router probably Bosch 1617 @ 7.7 pounds.
Then DW 618 fixed base.
http://www.patwarner.com (Routers)
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Wanting a smaller trim type router for hand held use around the shop with a
1/2" collet. The TR12 mainly stays in the router table, it being a 5
minute pain to remove, remove the plate, reinstall the old plate, change
the bit, use it, remove the bit, put the old bit back, remove the plate,
install the plate, reinsert into the table.

Alan