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Thread: Bellow compensation.

  1. #1

    Join Date
    Jan 2012
    Toronto, Canada

    Bellow compensation.

    Hi Gang.
    I have to premiss this question by saying that my knowledge of a LF camera and it's workings is extremly limited( never used one) and so this question might be in left field so bear with me.
    When you are taking an exposure reading should you compensate for the distance from the lens to the film or is the light loss minimal?

  2. #2
    IanG's Avatar
    Join Date
    Jan 2007
    Aegean (Turkey & UK)

    Re: Bellow compensation.

    Yes you must compensate for close up work, how much depends on the lens and the distance, there are tables published.


  3. #3

    Join Date
    Feb 2006

    Re: Bellow compensation.

    Try the homepage. Wonderful source of info.
    One man's Mede is another man's Persian.

  4. #4
    Light Guru's Avatar
    Join Date
    Jun 2011
    Salt Lake City, UT

    Re: Bellow compensation.

    If you have a iPhone, iPod Touch or iPad there is a great app called Reciprocity Timer that helps calculate bellows compensation and several other things effecting exposure.
    Zak Baker

    "Sometimes I do get to places just when God's ready to have somebody click the shutter."
    Ansel Adams

  5. #5

    Join Date
    Dec 2010
    Maryland, USA

    Re: Bellow compensation.

    Hi Louie,

    Bellows compensation is required any time a lens moves significantly forward from its infinity focus position,
    regardless of the format in use or the lens focal length.

    For example, if your image is life size (a 1:1 ratio between subject and image) you increase exposure 2 stops.

    Here's the actual page that explains it:

    The explanation is as follows:

    The lens projects a cone of light on the film plane.

    When focused at infinity, the height of the cone equals the lens focal length,
    and the light fills a circle at the film plane that has a particular diameter.

    As the lens moves away from the film, to focus on closer subjects, the diameter of that circle increases.
    Since the total amount of light does not change, the illumination per unit area decreases.

    When focused for 1:1, the distance from tilm to lens has increased to twice the focal length,
    so the area of the illuminated circle is four times its area at infinity, which is a 2-stop difference.

    - Leigh

  6. #6
    Join Date
    Jul 2001
    LA (Lethbridge, Alberta that is)

    Re: Bellow compensation.


    I have, on numerous occasions, recommended Bob Wheeler's freeware for those photographers who own what may (by some) be considered the outmoded hand-held Palm Pilot. It will provide, to a tength of a stop, the compensation for bellows extension with all formats of cameras... as well as a lot more for those who need tha accuracy. I doubt there are 'Apps' for the Android or the iPhone that will provide all or (similar) information that can be provided from this still available freeware.

    I only wish that I had been aware of this particular freeware when I was a "working" Technical/Scientific/Biological Photographer. It would have saved a LOT of time working out from the formulae, with the stubby pencil and a scrap of paper. Nowadays I never leave the house without making sure my Palm Pilot has 'good' batteries.


  7. #7
    Land-Scapegrace Heroique's Avatar
    Join Date
    Nov 2008
    Seattle, Wash.

    Re: Bellow compensation.

    Sheesh – how about a rule of thumb to ease our theoretical musings.

    I don’t worry too much about “correction” unless the distance to my subject is 10x my focal length, or closer.

    For example, w/ a 150mm lens, this threshold would be 10 x 150mm = 1500mm (1.5 meters).

    That’s pretty close.

    If I’m this close or closer – which is rare – my next rule of thumb is to add stop for every 25% increase in the bellows extension (beyond infinity).

  8. #8

    Join Date
    Mar 2012

    Re: Bellow compensation.

    If you are doing close-up still life, macro etc then yes, you do need compensation. Have a look at Quick disc I've found that quite helpful.

  9. #9

    Join Date
    Dec 2010
    Maryland, USA

    Re: Bellow compensation.

    Quote Originally Posted by Heroique View Post
    my next rule of thumb is to add stop for every 25% increase in the bellows extension (beyond infinity).
    That's correct in all situations.

    - Leigh

  10. #10

    Join Date
    Mar 2006
    Austin, TX

    Re: Bellow compensation.

    Focal length divided by bellow (similar measure) squared equals factor. Multiply ASA/ISO by the factor and that becomes your new film or sensor speed.


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