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Thread: Some naive questions about helicoid focusing for large-format

  1. #1

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    Some naive questions about helicoid focusing for large-format

    Apologies for beginning my first post with some very newbie questions and mistakes - I hope I can learn something useful and return the favor in the future. I should also add that I've googled and searched the forum, but I haven't found any definitive answer to my question - I hope you can excuse my ignorance, if I've missed some obvious search-terms.

    I've been interested in large format for a while, and decided to try my hand at (what I thought) was an 'easy' introduction by getting a camera with helicoid focussing, very few movements, and fitting a 6x9 film-back to the 4x5 back: a Cambo Wide 750.

    My assumption with the helicoid focussing, was that it would allow for hyperfocal focussing for landscapes in a similar way to 35mm - that is, by aligning the infinity marker with the correct f-stop marker (ie: if shooting at /22, aligning infinity with 22 on the lens, and stopping down to shoot without trying to check focus for the stopped-down, and obviously very dark, ground-glass image).

    Luckily I only exposed a few rolls of 120 film, because when I scanned these I could see that my assumption was completely wrong - the images are only really sharp for the first 3 or 4 meters in front of the camera, and then successively more blurred to the horizon.

    Now I guess a few experienced photographers are rolling their eyes - but I'd love to learn how to do this with large-format. Have I simply made totally wrong assumptions? How should one use the scales on a large-format camera? Or is it possible (unlikely I guess) that there's some fault with the lens calibration?

    With large-format, do I need front tilt to get everything in focus (from say 5 meters to the horizon)? Is such an aim even possible when working with negatives of this size?

    As an additional question, I think my ground glass is very dim and unsharp compared to examples I've seen on youtube videos. Where should I look for the brightest possible GG, especially recommendations from Europe?

    Many thanks for help!

  2. #2

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    Re: Some naive questions about helicoid focusing for large-format

    I think the helicoid in your camera simply needs to be adjusted to focus correctly. It sounds as if when you set the camera at infinity it is focusing closer than that. I use a CamboWide 750 and often use hyperfocal focus with it and it works well. I'm sorry that I can't help you with resources in Europe, but I would think that any competent repair service could take care of this for you.

  3. #3

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    Re: Some naive questions about helicoid focusing for large-format

    f22 for hyperfocal equals 4mm extension in focus difference. Is that how much you focus? Google the Linhof DOF scale chart for 4x5". The 1:○○ is for hyperfocal work.

  4. #4

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    Re: Some naive questions about helicoid focusing for large-format

    The lens on your camera is most likely a longer focal length than the one on your smaller camera. Therefore the depth of field at any given aperture is less.

  5. #5

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    Re: Some naive questions about helicoid focusing for large-format

    Quote Originally Posted by Richard Wasserman View Post
    I think the helicoid in your camera simply needs to be adjusted to focus correctly. It sounds as if when you set the camera at infinity it is focusing closer than that. I use a CamboWide 750 and often use hyperfocal focus with it and it works well. I'm sorry that I can't help you with resources in Europe, but I would think that any competent repair service could take care of this for you.
    Thanks Richard - this feels like a good news/bad news situation: apparently Im not a complete idiot, but on the other hand I now need to find someone who can fix the lens.
    I really appreciate your input - thanks again

  6. #6

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    Re: Some naive questions about helicoid focusing for large-format

    Each focal length lens has its own helical focusing mount. In fact, each 35mm lens from Rodenstock uses different helical mounts. The proper helical for your lens will have the same flange focal length as the lens without the helical.
    It sounds that the lens you are using is in the wrong focusing mount.
    Note, helical mounts for enlarging lenses are all the same. Unlike taking lenses.

  7. #7
    ic-racer's Avatar
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    Re: Some naive questions about helicoid focusing for large-format

    the images are only really sharp for the first 3 or 4 meters in front of the camera
    Large format cameras have higher levels of magnification than small hand-held cameras. This makes perceived depth of field smaller; due to the magnification. Focusing the view camera is the subject of whole books.

  8. #8
    Corran's Avatar
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    Re: Some naive questions about helicoid focusing for large-format

    What lens and what aperture did you shoot at and what was your focus distance set to?

    Does the Cambo have a ground glass back you can check focus/calibration with?

    If you are trying to compose an image with a close foreground element, getting full DOF will be tough without movements. But as already said, sounds like you might simply have a calibration issue.
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  9. #9

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    Re: Some naive questions about helicoid focusing for large-format

    Thanks for all the replies. I think I may have a go at calibrating the lens myself, based on this blog-post that I found:
    https://jakehornphotography.com/blog...al-calibration

  10. #10

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    Re: Some naive questions about helicoid focusing for large-format

    Quote Originally Posted by Jim Noel View Post
    The lens on your camera is most likely a longer focal length than the one on your smaller camera. Therefore the depth of field at any given aperture is less.

    Indeed - that's what I thought was my mistake, as described in my first post.
    But if my initial assumption about how focussing works with a helicoid on large-format was actually correct, then the depth-of-field scales on each lens should obviously be correct for that lens. In other words, I wasn't reading the distance and infinity setting from a 35mm lens and transferring it directly to the LF lens, I was using the scale markings on the LF lens itself. But that didn't work as expected.

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