Subject: Auto extention tubes

I recently bought a used Pentax 67 (in mind condition) with 2 lenses (165/2,8 and 90/2,8 LS) and the Auto Extension Tubes. I have 2 questions: 1) How do you calculate the DOF when using the Auto Extension Tubes? F. ex. the 165/2,8 with the Tube 1 (14 mm): Which formulae is applied here? 2) On the Aperture setting ring of both lenses there is a gab of a 1/2 stop between F 5,6 and 2,8. There are only 2 clicks here (instead of 3). For what Aperture do they stand for? Can anybody clarify this? Thank you very much for your responses.

-- Eugene Hertoghe (the.stores.company@bigfoot.com), February 09, 2002