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Thread: Bellow compensation.

  1. #1

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    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?
    Thanks.
    Louie

  2. #2
    IanG's Avatar
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    Re: Bellow compensation.

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

    Ian

  3. #3

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    Re: Bellow compensation.

    Try the homepage. Wonderful source of info. http://www.largeformatphotography.info/
    One man's Mede is another man's Persian.

  4. #4
    Light Guru's Avatar
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    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
    zakbakerphoto.com

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

  5. #5

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    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: http://www.largeformatphotography.in...ws-factor.html

    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
    KenS
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    Re: Bellow compensation.

    Louie..

    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.

    Ken

  7. #7
    Land-Scapegrace Heroique's Avatar
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    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

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    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 http://www.salzgeber.at/disc/ I've found that quite helpful.

  9. #9

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    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

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    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.

    Lynn

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