I've been trying to figure out the meaning of the somewhat cryptic instructions contained in the various Pentax bellows units and extension tubes. Some of the instructions give me the impression that the focusing rings of all lenses should be set at infinity when used with extension tubes (including macro lenses). Other instructions give me the impression that the focusing rings of all lenses except macro lenses should be set at infinity while macro focusing rings should be set at their closest focusing position.
Can anyone briefly explain the optical theory of lens extension and focusing ring settings? What about when lenses are reversed? Should macro lenses be set at infinity or at the closest focusing position? While I'm at it, what about the optical theory of close-up lenses (diopters) and focusing ring settings? Thanks for any and all replies. Tom Reese
