Ysterhout Dot Net
You need two light sources, so two torches are fine, one large and one small.
You need a stand for the rifle to be held while this operation is being done.
You need to do this in a room with no lights, so do it at night, and turn the room lights off when making the adjustments.
The flashlights need to be able to be fixed in place. Duct tape them to lamp stands if you need to.