Albert, you should be able to photograph your large adults without needing the extension tube if you are trying to do the entire body and not just a portrait. I only use manual focus when doing macro photography. It's really not possible to get the entire mantis in focus without stacking multiple images. I rarely stack and instead try to get the head, eyes and the closest legs in focus. Typically the larger the mantis, the easier it is for me to photograph. If you look at this image of a Yellow Orchid, only the head and forelegs are in focus. http://twolfephotos.smugmug.com/Animals-Insects/PrayingMantis/i-J4NWjSF/0/M/IMG_2013-01-02_5592-M.jpg If you photograph the mantis when the body is parallel to the camera, it's easier to get more of it in focus.