Results 1 to 5 of 5

Thread: bellows extension versus flange focal length?

  1. #1

    Join Date
    Sep 2003
    Posts
    1,794

    bellows extension versus flange focal length?

    This one is for the math majors -)

    If the flange distance is a fair bit different then the focal length which number do I plug into the formulas to calculate bellows needed to focus a certain distance?

    If the flange distance is 570mm I'd focus at infinity at 570mm of bellows right? Even if the focal length was 600mm.

  2. #2
    All metric sizes to 24x30 Ole Tjugen's Avatar
    Join Date
    Mar 2002
    Location
    Norway
    Posts
    3,383

    Re: bellows extension versus flange focal length?

    The flange distance is not an optical property of the lens. The focal length is.

    So with a 600mm lens with a 570mm flange distance, you add the difference needed to focus a 600mm lens to X distance to the flange distance to get the needed extension at X distance. The offset between the flange and the front focal node is constant for any given lens.

  3. #3

    Re: bellows extension versus flange focal length?

    Calculate the total extension using the focal length in formulas, and then subtract the focal length from the required extension. That value is the extension required beyond infinity focus. Add that value to the flange distance or any other distance measured on the camera when focused at infinity.

  4. #4

    Join Date
    Sep 2003
    Posts
    1,794

    Re: bellows extension versus flange focal length?

    Okay that makes sense.

    Thanks to everybody

  5. #5

    Join Date
    Nov 2003
    Posts
    1,219

    Re: bellows extension versus flange focal length?

    The easiest way to do it is as follows. Focus at infinity and note the position on the rail or bed of the standard you are using to focus. Then focus at the desired distance and note the new position. Find the distance between those two points.

    If you want to know the total bellows extension, just add that distance to the focal length.

    If you want to know the magnification, divide that distance by the focal length.

    If you want to know the fundge factor used to adjust exposure, add one to the magnification. If you multiply the marked f-number by that number, you get the effective f-number which should be used in exposure calculations. Alternately, use the marked f-number and multiply the time by the square of that number.

    The rear flange focal length would not be used for any of these calculations. You use it to estimate how close you can focus with a given bellows draw.

Similar Threads

  1. Ordering a super ultimate bellows for an Arca
    By Frank Petronio in forum Cameras & Camera Accessories
    Replies: 9
    Last Post: 31-Aug-2006, 16:56
  2. Bellows Extension versus Focal Length....
    By Michael Graves in forum Darkroom: Equipment
    Replies: 14
    Last Post: 6-Jul-2006, 20:13
  3. Schneider APO Tele Xenar 600/800mm Convertible
    By Eric Leppanen in forum Cameras & Camera Accessories
    Replies: 6
    Last Post: 6-Nov-2005, 22:43
  4. Fuji 600-C Flange Focal Length
    By Scott Rosenberg in forum Lenses & Lens Accessories
    Replies: 10
    Last Post: 31-Aug-2005, 10:08
  5. Minimum bellows extension and shortest focal at infinity
    By Nicholas F. Jones in forum Cameras & Camera Accessories
    Replies: 4
    Last Post: 24-Aug-2001, 11:16

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •