RRS wrote:
This works in the field or in a pinch too. Use three cans for shorter focal lengths and use five cans for the longer focal lengths. So you can see even three cans give you about 8", 4 on either side of center. Set the cans at about 20 degrees off center and so that the small print shows. Any questions?
The cans are unnecessary, that tape measure is the very best tool to use for the job all by itself.