Page 1 of 5 123 ... LastLast
Results 1 to 10 of 42

Thread: Bellows factor

  1. #1
    runs a monkey grinder Steve M Hostetter's Avatar
    Join Date
    Jul 2008
    Location
    Beech Grove Indiana
    Posts
    2,293

    Bellows factor

    Can anyone give me the bellows factor for 4 and 6 feet of bellows length.. thx

  2. #2

    Join Date
    Aug 2007
    Location
    Indianapolis, Ind.
    Posts
    589

    Re: Bellows factor

    Depends on the focal length of the lens used.

    required exposure time/metered exposure time = (image distance/focal length)^2

  3. #3
    runs a monkey grinder Steve M Hostetter's Avatar
    Join Date
    Jul 2008
    Location
    Beech Grove Indiana
    Posts
    2,293

    Re: Bellows factor

    405mm..lens

  4. #4
    Downstairs
    Join Date
    Feb 2008
    Location
    Italy
    Posts
    1,449

    Re: Bellows factor

    Maybe you could just put a 2-inch object in the set and read the factor off the Kodak BF strip on the groundglass. I mentioned elswhere that I keep a copy of the strip rolled up un a 2" tube.

  5. #5
    Joanna Carter's Avatar
    Join Date
    Oct 2006
    Location
    Plestin-les-Grèves, France
    Posts
    989

    Re: Bellows factor

    Quote Originally Posted by Steve M Hostetter View Post
    405mm..lens
    4ft is around 1200mm

    6ft is around 1800mm

    for 4ft - 1200^2 / 405^2 = 1440000 / 164025 = 8.8x or just over 4 stops

    for 6ft - 1800^2 / 405^2 = 3240000 / 164025 = 19.75x or around 5 1/3 stops

  6. #6
    runs a monkey grinder Steve M Hostetter's Avatar
    Join Date
    Jul 2008
    Location
    Beech Grove Indiana
    Posts
    2,293

    Re: Bellows factor

    Lets say If I used a probe and an 18% gray card would that give me basicly the same reading as an incident reading might ?

  7. #7

    Join Date
    Aug 2007
    Location
    Indianapolis, Ind.
    Posts
    589

    Re: Bellows factor

    Steve,

    If by probe, you mean the Sinar through the lens meter doohickey, then that automatically compensates for bellows factor (because it is through-the-lens.)

  8. #8
    Joanna Carter's Avatar
    Join Date
    Oct 2006
    Location
    Plestin-les-Grèves, France
    Posts
    989

    Re: Bellows factor

    Quote Originally Posted by Steve M Hostetter View Post
    Lets say If I used a probe and an 18% gray card would that give me basicly the same reading as an incident reading might ?
    That depends on whether there is enough light to activate the sensor.

    As you can see, the calculation really isn't that difficult :

    Bellows length (squared) divided by the focal length (squared) gives you the exposure factor.

    So, e.g. for & 210mm lens and a bellows of 420mm, the exposure factor is 4x, thus use 2 stops.

  9. #9

    Join Date
    Jan 2007
    Location
    Sonora, California
    Posts
    1,475

    Re: Bellows factor

    Quote Originally Posted by Joanna Carter View Post
    4ft is around 1200mm

    6ft is around 1800mm

    for 4ft - 1200^2 / 405^2 = 1440000 / 164025 = 8.8x or just over 4 stops

    for 6ft - 1800^2 / 405^2 = 3240000 / 164025 = 19.75x or around 5 1/3 stops
    Joanna got the first part (the multiplicative factor) correct. However, the conversion to stops is incorrect...

    8.8x is 3.1 stops
    19.75x is 4.3 stops

  10. #10
    Mark Sawyer's Avatar
    Join Date
    Jul 2004
    Location
    Stuck inside of Tucson with the Neverland Blues again...
    Posts
    6,266

    Re: Bellows factor

    It's much easier to just measure the aperture diameter through the front element, measure the bellows extension, and divide the latter by the former to get the actual f/stop. Much simpler than squaring one thing, then squaring another, then dividing, then translating the factor.

    It keeps you in touch with the simplicity of the focal length/aperture relationship. I never understood why so many large format photographers prefer the longer formula...
    "I love my Verito lens, but I always have to sharpen everything in Photoshop..."

Similar Threads

  1. Chamonix 45N-1 Universal bellows and Folding Viewer Review
    By BarryS in forum Cameras & Camera Accessories
    Replies: 15
    Last Post: 18-Feb-2009, 00:51
  2. Replies: 6
    Last Post: 13-Oct-2003, 11:19
  3. Arca Swiss Bellows Alternatives
    By tedkaufman in forum Gear
    Replies: 5
    Last Post: 18-May-2002, 20:16
  4. Bellows factor question
    By Rich Lingg in forum Gear
    Replies: 5
    Last Post: 24-May-2000, 21:26
  5. Formula for bellows factor
    By Bryan Fleishman in forum Style & Technique
    Replies: 3
    Last Post: 8-Jan-1999, 15:12

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
  •