RB67 - Auto Extension Tubes - Depth Of Field

Discussion in 'Medium Format Cameras and Accessories' started by Lyrrad, Jul 26, 2005.

  1. Lyrrad

    Lyrrad Member

    Feb 3, 2005

    Another question.

    I have a RB67 and the manual quotes DOF tables for each particualr lens. When using auto extension tubes is there a way of predicting new DOF info from original table?

    The manual does provide magnification range, distance range,and subject size range. It also gives exposure compansation values.
    Last edited by a moderator: Jul 26, 2005
  2. Marco Gilardetti

    Marco Gilardetti Member

    Jun 7, 2005
    Torino, Ital
    Large Format
    Jeez, this is where I'm actually toward learning rather than explaining. However, since nobody answered, my guess is the answer is no, as the formula for calculating DOF in the small distances range has a dependance on the subject to nodal point distance which is not linear, and however can't be approximated as usually it is at great distances. That is, you can't simply move the decimal point about one position, or divide everything by (say) 2, and get numbers which are still meaningful. That said in the macrophotography realm, I repeat, not at "normal" photographical distances. Please someone correct me if I misinterpreted the formula.

    However, you may not want to rely on those charts anyway, expecially in macrophotography. After all, the choosen "circle of confusion" on which these charts are based is never specified (or at least I've never seen one which reported it). I think it's better to rely on what you see on the ground glass, and mostly stop down as much as you can.