How close with a LF lens focus?

Discussion in 'Large Format' started by lauren_macintosh, Sep 3, 2007.

  1. If I learned anything and I hope I have this correct, All LF lens start
    focusing a Infinity [I think] But is there a chart or any thing that can tell
    you that 270mm lens the shortest it will focus or any other lens made , or is
    this by trial and error : Just plain curious :

    Since at Infinty the lens: Lets say a Four inch lens will start focusing at
    four inch and end maybe at five inchs: and I do know that a four inch Lens is
    100mm ! For those of you that feel I maybe wasting you time and Bandwith, I am
    sorry: and to those who respond I thank very much:
     
  2. Are you asking about how close a lens will focus? If so, this is determined by the bellows
    of your camera, not the lens.

    Alternatively, perhaps you are asking about depth of field? There are lots of charts on the
    web, so do a google search.

    By your question, I am guessing you are pretty new to photography. Might I suggest
    reading a book? At minimum it would help you find the correct vocabulary to ask your
    questions here more clearly. There are a number of books on LF photography, try your
    local library!

    ps: 1 inch = 25.4mm, so a 4" lens is 101.6mm
     
  3. pvp

    pvp

    Any lens will focus as short as you can imagine, limited by the length of the bellows. The farther the lens is moved from the film, the shorter the focus.

    I 'spose you'll also reach a limit when the subject impacts the front element of the lens...
     
  4. Wait A Minute Here: Please: Your saying that if my bellows goes to 18 inchs that the 100mm lens [sorry I just happen to round off] 101.6 lens will focus at that point? I have been reading Steve Simmons book and a kodak book Yes I am New to LF but not 35mm or med format, on 35mm to be come a close up you need extentions! since I thought was a simple question I guess My Lousey grammer composition wrecked the question: But your assuptions where right: {HOW CLOSE WILL A LARGE FORMAT LENS FOCUS] Thank you both for your answers:
     
  5. A lens focuses on infinity when positioned one focal length from the ground glass / film / digital sensor. As you move it farther away from the image plane, it focuses on closer subjects. On a view camera, the closest you can focus is limited by the maximum extension of the camera / bellows. The equations that give the quantitative answer are in Part I of the Lens Tutorial, http://www.photo.net/photo/optics/lensTutorial.

    The complication is that for full accuracy the distance from the image to the lens must be measured to a specific place on the lens, the rear principal point. But for most purposes, for LF lenses other than true telephotos, it is sufficiently accurate to measure to the center of the shutter.

    If you have a recent lens, you can probably find the location of the rear principal point from the manufacturer's datasheet. Another useful datum that is commonly provided is the "Flange Focal Distance". This is the distance from the rear of the flange (=back of shutter = front of lensboard) to the image when the lens is focused on infinity. The difference between this figure and the focal length will tell you the position of the rear principal point relative to the front of the lensboard.
     
  6. To answer all your non-telephoto lens focusing questions, apply the formula: "1/f = 1/o + 1/i". Accordingly, if you have 18" of bellows extension (and assuming you also have 18" of rail extension to fully utilize your 18" of bellows), and if you have a 4" lens; you will be able to focus onto a plane that is ca.: 5.14 inches from your lens when it is 18" from your ground glass.

    Flauvius
     
  7. Michael Briggs and Robert J Triffin, I thank you both very much
    for your help in this in formation on how close a Large format lens will focus: thank you vwery much and now I can move forward in this quest of mine: thank you ,Mr.Lauren MacIntosh
     
  8. "... on 35mm to be come a close up you need extentions..."
    This is exactly what the first two replies were talking about. For close focusing a 35mm camera, you add extension tubes to get your (normal) lens farther away from the film plane. For close focusing with LF, you rack out your bellows to do the same thing.
     
  9. If you have a LF camera, why not just rack the bellows out as far as they will go and see how close you can get to the subject?
     
  10. Mr.Bob Gentile: I thank you for showing my thought error, Sometimes what is in front of me can get the best of me! Maybe If I had thought about it more maybe I would came to that concluesion!
    Thank you very much:
     
  11. Mr.Nick Cooper: You are right and I di but like a fool I can be, I did not put anything close to the lens ,Instead was looking out the window and that does not work: Thank you very, [LOL]
     
  12. At infinity focus the lens is one focal length from the film and infinitely far from the subject.

    With an infinitely long bellows, the focus would be one focal length in front of the lens.

    So yes, there is a limit. How close to that limit you get depends on the length of the bellows.
     
  13. Ole: Thank you very much, at moment I am feeling like a fool , since I stated 35 mm and med format require extention tube's ,that to apply that to LF lens did not ring anything in my head to realize that the same principal was for all formats [ I think] thank for the extra Info:\\Lauren
     

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