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Thread: Close focussing distance

  1. #1

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    Close focussing distance

    I think I might be missing something fairly elementary but here goes.
    I have a Schneider Symmar S 150 mm lens on my Wista 45DX and have out of interest been researching its closest focussing distance.
    I appreciate that this depends on the amount of bellows extension. At full extension, there must be a limit to how close to the subject one can get. Is there a way of calculating this or is it achieved only by trial and error?

  2. #2

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    Re: Close focussing distance

    I think your 45DX has 13" of bellows -- there was a 45DX and a 45DXII, so I'm not sure. The easiest way to determine how close you can get is to extend the bellows all the way and then move the camera to see how close you can get. It's going to be about a foot -- and is easy to measure it. There are formulas you can use, but it depends on the focal length of your lens, the flange focal length of your lens, and the amount of extension of your bellows. But your setup will get you slightly greater than 1X magnification.

    For more magnification, you can get a shorter focal length lens (the most expensive alternation), an extension cone (hard to find), or close-up filters (pretty cheap, and expands your range of lenses for free):

    http://www.subclub.org/fujinon/close-up.htm

  3. #3

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    Re: Close focussing distance

    Well, minimum focusing distance is easy. 1 focal length, measured from the lens' front (subject facing) node. Since a Symmar's nodes (all versions) are near the diaphragm, measure from the diaphragm. Be warned that focusing at the minimum distance requires infinite extension so it isn't quite attainable.

    Minimum focusing distance with attainable extension is a little harder. Rear node-to-film distance given magnification and focal length is (magnification + 1) * focal length, so at the close focusing distance given extension and focal length magnification = (extension/focal length) - 1. Front node-to-subject distance = focal length * (magnification + 1)/magnification. Calculate the magnification you can get at maximum extension, plug the number into the second equation and there you are.

  4. #4

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    Re: Close focussing distance

    Dan is right that "minimum" focusing distance is simply a function of the focal length of the lens as long as you have unlimited bellows extension. I think his first sentence, however, really needs an eye-rolling, sarcastic emoji...

    I rather imagine, though, that you are more interested in the practical minimum with the maximum bellows extension available on your camera. The Wista DXs have 300mm of bellows extension, i.e., twice the focal length of the 150mm lens you have. So, with that you can get a 1-to-1 (life-size) image on your film. The distance from lens to subject you can figure out using the equation Dan gives above, or, you can simply do as xkaes suggests: rack your bellows all the way out and move the entire camera back and forth the focus. Once you've found focus, you can measure.

    Note, that if you plan on doing a lot of close up work, you'll find that moving the whole camera is a great tool to find the proper image size and focus. I prefer a monorail camera when I'm working close, since I can easily set a particular bellows extension and then, in essence, move the whole camera by simply moving both front and rear standards the same distance in the same direction.

    In practice, finding focus together with the desired magnification ends up being a dance between changing bellows extension and moving the whole set-up in relation to the subject. When you're doing this with a folding camera like the DX with just front focus, then you'll find you'll be inching the tripod around (or moving the subject itself, if practical) to find focus, then adjusting magnification if needed and repeating moving the whole camera in relation to the subject.

    If you plan on doing a lot of this with the Wista DX, you might want to rig yourself up a sliding tripod plate that allows you to slide the whole camera forward and backward by a couple of inches to facilitate the process.

    Best,

    Doremus

  5. #5

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    Re: Close focussing distance

    As an aside, in addition to all the great information above, also don't forget that when you have the bellows so far extended for maximum magnification, that you'll need to increase your exposure, usually significantly, to properly expose your film. Search "bellows factor" or just go here for what you need to know:

    https://www.largeformatphotography.i...ws-factor.html

    (if you have a camera with TTL metering you don't need to do all of the above, but very few LF cameras have TTL metering--some Sinars, Horseman had a film holder sized meter that you inserted like film, and I'm sure a few others--and most LF shooters are using a handheld meter, which will need adjustments to the exposure.)

  6. #6

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    Re: Close focussing distance

    Another way to ponder this question, how close is needed?

    Given the limits of camera/bellows extension with a 150mm lens, if getting closer is needed, another way to get closer would be to use a shorter focal length lens. Long as the lens is in shutter, most any lens that has a large enough image circle to meet the image goals can work good.

    More significant problem to getting "close" is camera support that is stable/rigid/vibration resistant and more important, lighting.


    Bernice


    Quote Originally Posted by JohnF View Post
    I think I might be missing something fairly elementary but here goes.
    I have a Schneider Symmar S 150 mm lens on my Wista 45DX and have out of interest been researching its closest focussing distance.
    I appreciate that this depends on the amount of bellows extension. At full extension, there must be a limit to how close to the subject one can get. Is there a way of calculating this or is it achieved only by trial and error?

  7. #7
    ic-racer's Avatar
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    Re: Close focussing distance

    The closest focusing distance is always 4 times the focal length. That is the closest your camera (film) can get to the subject and still have the ability to project a focused image.
    Or did you ask about highest magnification, which is, as Dan Fromm points out, the FARTHEST the film will be from the subject (infinity).

  8. #8

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    Re: Close focussing distance

    Quote Originally Posted by ic-racer View Post
    The closest focusing distance is always 4 times the focal length. That is the closest your camera (film) can get to the subject and still have the ability to project a focused image.
    Or did you ask about highest magnification, which is, as Dan Fromm points out, the FARTHEST the film will be from the subject (infinity).
    This is exactly correct, but it's not intuitive. The film plane needs to be at least 4 times the focal length from your subject. With a folding view camera, like the Wista, you'll be doing focusing with the front standard, so if you put your camera film plane too close to your subject you'll never be able to focus even if you get super long bellows or an extension device. It IS possible to get the LENS very close to the subject (up to 1 focal length), but the bellows will need to be very long, as others have stated, and the film plane will be much more than 4 times the focal length from the subject.

    With a 150mm lens, 4 times the focal length is 600mm (about 2 feet), so the film holder needs to be greater than 2 feet from your subject. If you want to focus closer, you'll actually have to move the camera further away from your subject and then move the front standard closer. That's why it's not intuitive.

  9. #9

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    Re: Close focussing distance

    Good point, Sharktooth. You didn't say it explicitly, but the minimum film plane to subject distance is 4 * focal length. Magnification is 1:1. At magnifications around 1:1, its good practice to set the camera/lens assembly up for the desired magnification and then to focus by moving the camera/lens assembly or the subject. Focusing on a near subject by moving a standard risks getting the subject in focus at the desired magnification's conjugate. Conjugate? Film-to-subject distance at 1:n is the same as film-to-subject distance at n:1.

  10. #10
    Jim Jones's Avatar
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    Re: Close focussing distance

    While this thread has stressed the theory of close-up photography, there also are practical problems. The image quality from some lenses decreases at close focal distances. Also, retro-focus and telephoto lenses behave differently than simple lens theory predicts when used outside their normal ranges. For optimum image quality in micro-photography, lenses are often reverse mounted. The problems with this should be considered when planning micro-photography.

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