Crown and flint when put together produces a coated achromatic objective lens 71.9mm diameter with a focal length of 700mm Great for making an inexpensive but quality scope. Place the crown (double convex) with its strongest curve against the negative side of the flint. Use a couple pieces of masking tape on the edges to hold them together. The crown side faces the sky or the object you plan to look at. For best results use a 3 or 4 small pieces of masking tape at the edge between the two elements to separate them so they don’t touch. Unused.
