I recently had to start using an optical device while modeling. I was told, by several fellow modelers, that the OptiVISOR LX is the best way to go. The OptiVISOR is made by Donegan Optical Co. (http://www.doneganoptical.com/
) These can be purchased/ordered by most local hobby or train shops. They run about $30-50.00USD. I recommend the LX-3, it's 1.75 magnification at 14inches. The LX-7 is 2.75 magnification at 6inches distance.
Hope this helps,