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Thread: Use of plus lenses to shorten bellows draw.

  1. #11
    Tin Can's Avatar
    Join Date
    Dec 2011
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    22,383

    Re: Use of plus lenses to shorten bellows draw.

    ...and?

    Quote Originally Posted by Neal Chaves View Post
    I am trying to understand what is going on here and why it rates an "attaboy". The camera was set up and focused to photograph the waterfall and pool but the 300mm lens was too long for the desired composition. So then, a plus lens was added added without refocusing, and voila, now we see the visualized composition, but now probably nothing closer than about 12-24 inches is in focus. When any lens is focused closer, the image circle increases, and it has here. Since there is nothing on the plane on which the lens is focused this is not immediately apparent. I'd like to see a branch or flower sticking up into the foreground on the plane of focus, wherever that was.
    Tin Can

  2. #12
    Nicholas O. Lindan
    Join Date
    May 2006
    Location
    Cleveland, Ohio
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    462

    Re: Use of plus lenses to shorten bellows draw.

    Quote Originally Posted by Bernice Loui View Post
    Simply does not apply to a proper view camera that can support virtually any lens.. Like this... again.
    Attachment 221206
    That's not a camera, that's a seismograph!

    In my book anything that helps get you the picture is OK. Purity for purity's sake is a dead-end.

    Negative lenses, in addition to positive "close-up" lenses, were available at one time for the purpose of increasing a lens' focal length.

    FWIW, the formula for focal length adjustment:

    New focal length in mm = 1000 / ((1000/lens focal length in mm) + diopter)

    Easier in meters: new fl = 1/(1/fl + d)

    As an example, a 300mm lens with a +2 close up lens will have a ~190mm effective focal length.
    Darkroom Automation / Cleveland Engineering Design, LLC
    f-Stop Timers & Enlarging meters http://www.darkroomautomation.com/da-main.htm

  3. #13

    Join Date
    Sep 2010
    Posts
    831

    Re: Use of plus lenses to shorten bellows draw.

    So the effective focal length of the 300mm lens used in the photo above would be 232mm. Now can we know where the lens was focused when it was decided that a +1 was needed to "increase the size of the field", which it certainly did do, but I think the intent was rather an attempt to widen the angle of view? Let's say it was thirty feet out, you could then calculate how much bellows was drawn. Knowing this, and that when you add the +1, the lens is now a 232mm, you smart guys could determine the distance to the new plane of focus.

  4. #14

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    Feb 2015
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    Sheridan, Colorado
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    Re: Use of plus lenses to shorten bellows draw.


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